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362 Cards in this Set
- Front
- Back
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Describe the origin of the mitochondria.
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- Purple bacteria (aerobic microorganisms) invaded anaerobic hosts
- Conferred ability for oxidative metabolism (endosymbiosis) |
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What are the implications of mitochondria originating from purple bacteria?
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Vulnerable to antibiotics
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What are the functions of mitochondria?
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- Complete oxidative metabolism of carbohydrates, amino acids, and fatty acids
- Coupling of electron transport and oxidative phosphorylation for the generation of ATP |
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How do mitochondria (originally bacteria) benefit from being in eukaryotic cells?
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Eukaryotic cell provides majority of proteins and enzymes for mitochondrial biogenesis and function
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Where are mitochondria located?
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Localized near sites of high ATP utilization
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What is required for successful endosymbiosis between eukaryotic cells and mitochondria?
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- Coordination of mtDNA and nuclear DNA for the synthesis, assembly, and functioning of respiratory chain enzymes
- Euk cell supplies majority of proteins and enzymes - Mito supplies ATP for cell |
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What are the four compartments of the mitochondria?
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- Outer Mitochondrial Membrane (OMM)
- Inter-Membrane Space (IMS) - Inner Mitochondrial Membrane (IMM) - Mitochondrial Matrix |
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What are the components of the outer mitochondrial membrane (OMM)?
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- Porin or VDAC (voltage-dependent anion channel)
- Receptors - TOMs (translocases of OMM) |
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What are the components of the inter-membrane space (IMS)?
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- Cytochrome C
- Adenylate Kinase (interconversion of ATP, ADP, and AMP) |
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What are the components of the inner mitochondrial membrane (IMM)?
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- Cardiolipin
- Respiratory chain enzymes (Complexes I, II, III, IV, and V) - Transport proteins (ATP-ADP translocase) - TIMs (translocases of MM) |
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What are the components of the mitochondrial matrix?
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- Krebs Cycle enzymes
- Peptidases - mtDNA - Ribosomes - Ca2+ |
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What is the electrical gradient within the mitochondria?
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Inside (-): basis for membrane potential and proton gradient
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What is the chemiosmotic theory?
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- Coupling of electron transfer to oxidative phosphorylation
- Intermediate of this coupling is the electrochemical proton gradient across the inter-mitochondrial membrane (IMM) |
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What are the two components of the electrochemical proton gradient across the IMM?
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- Membrane potential (ΔV) = large force
- H+ concentration gradient = smaller force - Both forces have inside negative |
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What processes are driven by the electrochemical proton gradient across the IMM?
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- ADP/ATP antiport
- H+/Pi- symport - H+/Pyruvate symport - Various translocases in OMM and IMM for protein import |
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How do mitochondria replicate?
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Binary fission of existing mitochondria
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Describe the human mitochondrial DNA structure.
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- ~17,000 bp
- Double stranded (Heavy, H, & Light, L, strands) - No introns |
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What genes does human mitochondrial DNA code for?
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- 2 rRNAs (12S and 16S)
- 22 tRNAs - 13 polypeptide-encoding RNAs (7 subunits for complex I, 0 subunits for complex II, 1 subunit for complex III, 3 subunits for complex IV, 2 subunits for complex V) |
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What is found on the "D loop" of the human mitochondrial DNA H strand?
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- Origin of replication for heavy strand (O_H)
- Promoters for heavy (P_H) and light (P_L) strands - 3 conserved sequence blocks (CSB) - Termination-associated sequences (TAS) |
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How does replication happen on the human mitochondrial DNA?
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- Bidirectionally
- Asynchronously - Semiautonomously: not dependent on cellular division |
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How does transcription occur in human mitochondrial DNA? Which genes are the most commonly transcribed?
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- Symmetrically from 2 promoters in D-loop
- rRNA (12S and 16S) transcripts outnumber the other transcripts |
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What are the unique codons of mitochondrial DNA? What do they usually code for?
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- AGA or AGG: Arg --> STOP
- AUA: Ile --> Met - UGA: STOP --> Trp |
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How is mitochondrial DNA inherited?
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From maternal side
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When does replicative segregation of mtDNA occur?
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During mitosis and meiosis
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How often do mutations occur in mtDNA replication vs. nuclear DNA?
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10-20x more often (very high)
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What does it mean for the mtDNA mutations to have a threshold expression?
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When the threshold level is crossed, the cell, and in turn the organ, will suffer
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What is the role of the nuclear genome in mitochondrial biogenesis?
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- Specifies all enzymes of mitochondrial matrix
- Cooperates with mtDNA in synthesis of multisubunit enzyme complexes of oxidative phosphorylation - Encodes all components of protein import machinery - Encodes transcription factors for mtDNA transcription & replication, & for proteins targeting mito - Controls translation of specific mito mRNAs - Controls processing of specific mito RNA precursors |
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Why is it important to have components of protein import machinery for mitochondria?
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~99% of mitochondrial proteins have to be imported
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Describe the targeting sequence aka precursor that targets protein import for the mito?
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- 20-70 AA
- Rich in basic and hydroxylated AA at N-terminus - Can form amphipathic structures - Cleaved by specific peptidases in mito |
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What is the mechanism / what is involved in protein import into mitochondria?
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1. Targeting sequence on N-terminus of protein
2. Cytosolic chaperones (e.g. Hsp70) hydrolyze ATP to unfold protein 3. Import receptors on OMM bind protein 4. Translocation across OMM (via general insertion protein, GIP) and across IMM (via translocase of inner mito membrane, TIM) 5. MIA pathway proteins (machinery for protein import and assembly) and small IMS proteins (TIMS) assist with sorting and assembly of proteins in IMS and IMM 6. Use proton-motive force to transport protein across IMM 7. Translocation motors (mtHsp70 and ATP) found in matrix help pull protein through membrane 8. Proteolytic processing of matrix-targeting signals 9. Refolding, assembly and intromitochondrial sorting via chaperones (Hsp60 and ATP) |
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Which three components of protein import into mito requires ATP?
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- Cytosolic chaperones (e.g., Hsp70) requires ATP hydrolysis to unfold proteins prior to import
- Translocation motor: mtHsp70 hydrolyzes ATP to pull protein through membrane during translocation - Refolding, assembly, and intramitochondrial sorting by chaperonins (e.g., Hsp60) hydrolyzes ATP |
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What are three possible sources of mutations in mitochondria?
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- Nuclear DNA (Mendelian inheritance)
- Cytoplasmic mtDNA (non-Mendelian, maternal inheritance) - X-linked |
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Why is mtDNA prone to mutations?
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- mtDNA attached to IMM, source of radical oxygen species (ROS)
- mtDNA lacks protective histones - mtDNA has limited repair system |
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What are the four types of mutations that can be seen in mtDNA?
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- Missense mutations: amino acid substitutions
- Biogenesis mutations: tRNA point mutations affects protein synthesis - Insertion-deletion mutations: deletions of 1.3-7.6 bp - Copy number mutations |
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What is an example(s) of a disease that has a missense mutation (AA substitution) for mtDNA?
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LHON (Leber's Hereditary Optic Neuropathy)
- Become blind rapidly |
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What is an example(s) of a disease that has a biogenesis mutation for mtDNA (tRNA point mutations)
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- MERRF (myoclonus epilepsy and ragged red fibers) - seizures, abnormally large mitos, multi-system defects
- MELAS (mitochondrial encephalomyopathy, lactic acidosis, and strokelike symptoms) |
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What is an example(s) of an insertion-deletion mutation for mtDNA?
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- KSS (Kearns Sayre syndrome)
- PEO (progressive external ophthalmoplegia) - Deletions of 1.3-7.6 bp often flanked by direct repeats of nucleotides - Usually no family history (most deletions are new occurring during development) |
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What are some problems of aging that are normal that are related to mitochondrial dysfunction?
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- Reactive O2 species - major mtDNA damaging agents
- mtDNA deletions accumulate with age - Oxidative phosphorylation declines with age |
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What happens to oxidative phosphorylation with age?
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Declines
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What two diseases have defective energy metabolism often associated with them (not the cause)?
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- Parkinson's disease (paralysis agitans)
- Alzheimer's disease - Diabetes |
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How are mitochondria involved with apoptosis?
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- Cytochrome c stored in inter-membrane space of mito
- Release is an early event in apoptosis |
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What steps trigger apoptosis?
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- Cytochrome c released from mito
- Cyto c binds to Apaf-1 (apoptotic protease activating factor 1) - Binds to caspase 9 - Caspase 9 activated - Caspase 3 activated - Apoptosis triggered |
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Which proteins block release of cytochrome c from mitochondria? How does this affect apoptosis?
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- Bcl-2 and Bcl-XL
- Prevents apoptosis, promotes cell survival |
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Which proteins are pro-apoptotic?
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Bad and Bax
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Where are Bcl-2 family proteins often found? What kind of factors are they?
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Outer mitochondrial membrane (OMM); anti-apoptotic (promote cell survival)
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What is the purpose of the electron transport and oxidative phosphorylation?
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Allows cell to convert energy of NADH and FADH2 into energy of ATP
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How is the energy transferred n the electron transport chain from NADH/FADH2 to ATP?
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As electrons flow from one carrier to the next down an energy gradient, the electrons do work which is pumping protons OUT of the mito matrix
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What is the ultimate purpose of breathing?
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O2 is reduced to H2O in the electron transport chain to set up the proton gradient so that ATP can be synthesized
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Where are the electron transport carriers and the ATP synthesizing unit located?
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Inner membrane of mitochondria
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The inner mitochondrial membrane is impermeable to what?
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Charged species; they can cross only if there is a specific carrier for them (including ADP, Pi, and ATP)
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In what direction does the ATP-ADP translocase usually move ATP and ADP across the inner mitochondrial membrane?
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- ADP is moved into the matrix
- ATP is moved out of the matrix (into the cytoplasm) |
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What are some important metabolite transporters in the inner mitochondrial membrane?
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- ATP-ADP translocase (ADP in to matrix, ATP out of matrix)
- Dicarboxylate carrier (malate out of matrix, PO4 in) - Tricarboxylate carrier (citrate + H+ out of matrix, malate into matrix) - Pyruvate carrier (pyruvate into matrix, OH- out) - Phosphate carrier (PO4- into matrix, OH- out) |
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What is the other name of the ATP-ADP translocase? How does it function?
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ANT "Adenine Nucleotide Translocase"
- ADP accumulates from cell work in cyto and is transported into matrix - ATP is made in matrix and transported out |
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How can NADH that is generated in the cytosol be delivered to the mitochondrial matrix?
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Two shuttles which deliver reducing equivalents (electrons, not the NADH molecule itself)
- Glycerol Phosphate Shuttle - Malate-Aspartate Shuttle |
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Where is the glycerol phosphate shuttle (which delivers reducing equivalents to mito matrix) active?
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Skeletal muscle and brain
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The glycerol phosphate shuttle (which delivers reducing equivalents to mito matrix) transfers electrons to what molecules?
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(reduced FAD and Coenzyme Q)
- NADH + H+ oxidized to NAD+, passing electrons to dihydroxyacetone-P to convert it to glycerol-3P - Glycerol-3P passes 2e- to FAD to convert it to FADH2 (while returning to dihydroxyacetone-P) - FADH2 passes 2e- to Coenzyme Q in IMM to make QH2 (returning to FAD) - Coenzyme QH2 is then able to donate 2e- to complex III |
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Where is the malate-aspartate shuttle (which delivers reducing equivalents to mito matrix) active?
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Liver and heart
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The malate-aspartate shuttle (which delivers reducing equivalents to mito matrix) uses what reactions?
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- NADH oxidized to NAD+, passing 2e- to oxaloacetate to make malate
- Malate shuttled across IMM - Malate passes 2e- to new NAD+ in matrix to reduce it to NADH (reforming oxaloacetate) - Glutamate transfers amino group to oxaloacetate, to make aspartate (glutamate converted to α-ketoglutarate) - α-ketoglutarate and aspartate sent back across IMM to cytoplasm (by separate transporters) - In cyto, aspartate donates amino group back to α-ketoglutarate to reform oxaloacetate and glutamate - Glutamate sent back into matrix; oxaloacetate ready to take 2e- from NADH |
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Does the NADH molecule in the cytoplasm enter the matrix via the malate-aspartate shuttle?
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No, the 2e- from NADH ride in on malate and make a new NADH from NAD+ in the matrix
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How many electrons are required to reduce NAD+ to NADH?
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2 e- always
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How many electrons are required to reduce FAD and FMN?
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1 or 2 e- (FADH/FMNH vs FADH2/FMNH2)
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What is the significance of the portion of the NAD+/NADH/NADP+/NADPH molecule that is not part of the reactive site (gaining/losing H/e-)?
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Either contains or doesn't contain P, which gives molecule specificity
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Describe the electron carrier ubiquinone (Coenzyme Q).
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- Lipid-soluble
- Part of Complex I - Also exists as a freely mobile e- carrier inside mitochondrial inner membrane - Can accept 1 or 2 e- |
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When ubiquinone (Q) accepts only one e-, what does it form?
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- Semiquinone anion; radical version that can cause damage as an oxidant
- Accepting another e- converts it to ubiquinol (QH2) |
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Describe the role of an iron-sulfur cluster?
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- Electron carrier / transport complex
- Involved in pumping protons - Iron atoms can be oxidized (Fe3+) or reduced (Fe2+) - Accepts 1 e- at a time |
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Which electron carrier(s) require the vitamin riboflavin for synthesis?
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FMN and FAD
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What are the two kinds of S in Fe-S centers?
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Cysteine S and sulfide S (H2S) which is actually sulfane S (S0)
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What is the function of cytochrome c?
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- Slides along outer surface of mitochondrial inner membrane
- Carries e- between complex III and IV |
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What is the structure of cytochromes?
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Small proteins with heme groups bound to them (Fe2+ or Fe3+ in center of heme group)
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What is the purpose of electron transport / oxidative phosphorylation?
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To couple highly exergonic reactions (NADH oxidation by O2) to a highly endergonic reaction (ATP synthesis from ADP and Pi)
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What is the ∆Go for transfer of e- from NADH to O2?
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-52 kcal/mol
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What is the ∆Go for synthesis of ATP from ADP and Pi?
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+7.5 kcal/mol
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Very basically, how is the energy from NADH oxidation by O2 harnessed to synthesize ATP?
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- NADH transfers electrons indirectly through multiple e- carriers organized in 3 complexes (I, III, and IV)
- As e- pass through complexes, some energy is released to pump H+ out of mito matrix (∆Go > 0, but balanced by ∆Go < 0 from NADH oxidation) - When H+ flow back into matrix, the ∆Go < 0 and the energy is used to synthesize ATP |
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In what stages of the electron transport chain is the most energy released?
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- From NADH to CoQ
- From Cytochrome C to O2 |
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In which complexes of the electron transport chain are there Fe-S complexes?
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Complex I, II, and III
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In which complexes of the electron transport chain are there cytochromes?
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Complexes III and IV
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What are some of the strongest oxidants (relevant to electron transport chain)? Do these molecules have a high or low affinity for e-?
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- O2 + 2H+
- Fe3+ - Cytochrome c (3+) - Ubiquinone (CoQ) Have a high affinity for electrons (oxidants become reduced; reduced is gaining e-) |
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What are some of the strongest reductants (relevant to electron transport chain)?
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- H2
- NADH - NADPH - FADH2 Have a low affinity for electrons (reductants become oxidized; oxidized is losing e-) |
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Do strong oxidants or strong reductants have a more positive E'?
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Strong oxidants have positive E' values; strong reductants have negative E' values
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An oxidation-reduction reaction is thermodynamically favored if e- flow towards a positive or negative E'?
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Towards the most positive E' (strong oxidants)
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What is the equation for ∆Go' (related to reduction potential)?
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∆Go' = - n F (∆E)
n = number of electrons F = Faraday's constant (23 kcal/V) ∆E = E' (e- acceptor) - E' (e- donor) *Remember, strong oxidants (like O2) have a positive E'; strong reductants (like NADH) have a negative E' |
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What is the equation for ∆E' (reduction potential)?
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∆E = E' (e- acceptor) - E' (e- donor)
Therefore, if e- acceptor is a strong oxidant (high affinity for e-) and e- donor is a strong reductant (low affinity for e-) than the ∆Go' will be negative (thermodynamically favorable) *Also, because a minus is included in the equation, you don't need to change the value, leave the values as are in the table (don't change sign) |
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Does the stoichiometric coefficient of e- matter for calculating ∆E (reduction potential)?
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No, you never multiply by coefficients in redox problems; electrical potential is an intrinsic property so it stays same regardless of stochiometry
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Describe the electron flow through the electron transport chain at Complex I.
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- An e- pair from NADH passes through complex I to ubiquinone (CoQ)
- 4 H+ are pumped from matrix to intermembrane space |
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Describe the e- flow through the electron transport chain at Complex II.
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- Succinate is oxidized to fumarate (succinate dehydrogenase)
- 2 e- passed from succinate to CoQ |
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Describe what happens at Complex III of the electron transport chain.
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- From CoQ(H2), electrons are delivered to cytochrome c (Fe3+), oxidizing it to Fe2+
- 2 H+ pumped out of matrix |
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Describe what happens at Complex IV of the electron transport chain. What is another name for Complex IV?
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- Cytochrome c (Fe2+) delivers e- to complex IV
- 4 H+ are pumped out of matrix (actually, 4H+ are consumed by reduction of O2 to 2 H2O, thus it's a net gain of 4H+ in intermembrane space; more about the gradient than actual pumping) - 1/2 O2 is reduced to H2O for each pair of e- that arrive (so really O2 reduced to 2 H2O by 4 e-) - AKA: Cytochrome Oxidase |
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At which complex are no protons pumped?
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Complex II (succinate dehydrogenase)
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One molecule of NADH pumps how many protons across the inner mitochondrial membrane out of the matrix?
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10 H+
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One molecule of FADH2 pumps how many protons across the inner mitochondrial membrane out of the matrix?
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6 H+ via Complexes III and IV (because it does not enter at complex I so misses out on those 4 H+)
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How many protons must flow back across the inner mitochondrial membrane to synthesize 1 ATP?
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4 H+: 1 is used to bring Pi into matrix and 3 are used by Fo-F1-ATPase
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The Fo-F1-ATPase is also called what?
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Complex V
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How many ATP can one molecule of NADH "synthesize"?
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2.5 ATP
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How many ATP can one molecule of FADH2 "synthesize"?
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1.5 ATP
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From what sources does Coenzyme Q receive e-?
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- Complex I (oxidation of NADH gives 2 e- to CoQ)
- Complex II (succinate dehydrogenase; succinate oxidized to fumarate, gives 2 e- to CoQ) - Glycerol-3P shuttle - One step in FA oxidation (fatty acyl-CoA --> enoyl-CoA) |
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Spectrophotometrically, the redox state of NAD+ / NADH or cytochromes can be measured; what peaks show up if NAD+ vs NADH is high?
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- More NAD+ = peak at 260 nm
- More NADH = higher peak at 260 nm and peak at 340 nm |
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What is important for the regulation of electron flow through e- transport chain?
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- Tightly controlled by proton pumping
- e- can flow only if H+ are pumped - If H+ gradient is too large, there is not enough energy available for e- to flow, flow stops until gradient is diminished by ATP synthesis (or some other way) |
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Describe what "State 3" means for a mitochondria?
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- Normal for a working mitochondria
- High NADH - High O2 - High ADP - Fast respiration rate - Respiratory chain is rate-limiting |
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What are the steady-state percent reduction of NAD, Flavin, Cytochromes B, C, and A for a mitochondria in "State 3" (working)?
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- NAD: 53% reduced
- Flavin: 20% reduced - Cyto B = 16% reduced - Cyto C = 6% reduced - Cyto A = 4% reduced |
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Describe what "State 4" means for a mitochondria?
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- Resting mitochondria
- High NADH - High O2 - Low ADP - Slow respiration rate - ADP is rate-limiting |
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What are the steady-state percent reduction of NAD, Flavin, Cytochromes B, C, and A for a mitochondria in "State 4" (resting)?
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- NAD: 99% reduced
- Flavin: 40% reduced - Cyto B = 35% reduced - Cyto C = 14% reduced - Cyto A = 0% reduced |
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How does the steady-state percent reduction of NAD, Flavin, Cytochromes B, C, and A for a mitochondria compare when working vs. resting?
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- Working Vs. Resting
- NAD: 53% vs 99% reduced - Flavin: 20% vs 40% reduced - Cyto B = 16% vs 35% reduced - Cyto C = 6% vs 14% reduced - Cyto A = 4% vs 0% reduced |
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How does the amount of NADH, O2, and ADP compare for a working (state III) vs resting (state IV) mitochondria?
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- Both High NADH
- Both High O2 - High ADP (working) vs low ADP (resting) |
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How does the respiration rate compare for a working (state III) vs resting (state IV) mitochondria?
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Fast (working, state III) vs Slow (resting, state IV) respiration rate
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How does the rate-limiting factor for the respiratory chain compare for a working (state III) vs resting (state IV) mitochondria?
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- Respiratory chain is rate-limiting factor for working mitochondria
- ADP availability is rate-limiting factor for resting mitochondria |
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What are some poisons of the electron transport chain?
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- Cyanide (CN-) and Carbon Monoxide (CO) - both inhibit Complex IV potently but reversibly
- Nitric Oxide (NO) - inhibits complex IV reversibly and at high levels destroys FeS centers of complexes I and II |
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How can you treat cyanide (CN-) poisoning (which inhibits complex IV)?
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- Administration of nitrite
- Converts Hb to metHb to bind cyanide - Then give thiosulfate to allow metabolism of cyanide to less toxic thiocyanate by rhodanese |
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What is the meaning of the P/O ratio?
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- Measure of phosphorylation efficiency
- Refers to number of high energy phosphate bonds formed (i.e., ATP formed) per 1/2 O2 reduced to water - E.g., NADH has upper limit of 2.5, FADH2 has upper limit of 1.5 |
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What is the meaning of the respiratory control index?
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Measure of how tightly mitochondrial respiration (use of O2) is coupled to ATP synthesis
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What would cause the respiratory control index to be low
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If a drug or natural process allows protons to flow back into matrix without making ATP (e.g., in brown adipose tissue, themogenin uncouples proton flow from ATP synthesis)
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What does the protein thermogenin do?
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- AKA uncoupling protein 1 (UCP1)
- Allows protons to leak back into mitochondrial matrix without synthesizing ATP - Heat generated in brown adipose tissue (BAT) allows non-shivering thermogenesis |
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What is the efficiency of the energy capture by ATP synthase? How is it calculated?
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35%:
- NADH oxidation to NAD+ has a ∆Go' of -52.6 kcal/mol - ATP synthesis requires 7.3 kcal/mol of energy - Efficiency = 2.5 (7.3) / 52.6 = 35% |
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What is the chemiosmotic hypothesis by Peter Mitchell?
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Electron transport generates a proton gradient across the mitochondrial inner membrane; that gradient supplies the energy for ATP synthesis
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How does the pH compare in the matrix to the inter-membrane space?
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pH is 1.4 units lower in inter-membrane space than in matrix
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What is the membrane potential across the inner mitochondrial membrane?
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0.14 V (inter-membrane space more positive than matrix)
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What are the two components of the proton-motive force?
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- Membrane potential contribution (Em = 0.14V)
- Chemical gradient contribution (∆pH = 1.4) |
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Is the electron transport more or less efficient than ATP synthesis?
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More efficient: virtually all the energy of NADH is captured in the proton gradient
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What is the mechanism of ATP synthesis?
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- ATP synthase has Fo-subunit in membrane and F1-subunit attached to it on matrix side)
- Protons flow through ATP synthase back into matrix, down energy gradient, forcing the γ-subunit to rotate - Conformation changes cause conversion of ADP + Pi (L) to make ATP (T) and to be released (O) |
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What are the subunits of the F1-subunit of ATP synthase?
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- 3 α,β-subunit pairs
- γ-subunit in center |
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The three α,β-subunits pairs are in what three possible conformations? What does each of these conformations doe?
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- L = loose, binds ADP and Pi
- T = tight, makes ATP - O = open, releases ATP |
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How many ATP are generated by a full turn of the γ-subunit? How many protons must flow through?
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3 ATP; 9 protons (1 H+ per ATP does not flow through ATP synthase)
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If ADP levels are low and the L site is not occupied, what happens?
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γ-subunit stops rotating and no additional synthesis of ATP occurs
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What is the key control mechanism for regulating levels of ATP?
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γ-subunit will not continue rotating unless there is an ADP bound to the L subunit
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ATP is made and released into the matrix, how does it get out to the cytoplasm?
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ATP-ADP translocase (aka ANT for adenine nucleotide translocase)
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Why is brown fat more brown than normal fat?
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More vascular; lots of mitochondria for heat generation via thermogenin
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How does the protein content of the mitochondria in BAT compare to normal mitochondria?
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- BAT have less Fo-F1 ATPase levels
- More thermogenin (UCP1) in membrane for uncoupling of H+ gradient |
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Where is brown fat distributed on a baby? How much of a baby's weight is from brown fat?
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- Within body just outside pleural and peritoneal membranes
- Anterior portion of shoulders and over heart on anterior and posterior sides - Posterior side where kidneys are located |
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How can you detect presence of brown fat (BAT) in adults?
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PET scan using 18F-fluro-deoxyglucose (FDG) as a probe
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When is brown fat (BAT) more common in adults?
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In thin people, especially women
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What is the pathway by which thermogenin (UCP1) is activated?
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- Exposure to cold stimulates nerves in BAT to release NE (adrenergic stimulation)
- NE activates hormone-sensitive lipase to release free fatty acids (FFA) from triglycerides (TG) - Metabolism of FFA generates acetyl-CoA, then NADH and FADH2 - NADH and FADH2 contribute to proton gradient - FFA also activates UCP1 which allows protons to flow back into matrix, generating heat - Glucose can also be a fuel |
|
|
Why is propranolol used when doing a PET scan for tumors?
|
- Brown fat shows up on PET scan and may disguise tumors
- When propanolol is used the brown fat does not show up and tumors are less likely to be missed |
|
|
What other ways can protons leak back into the matrix aside from ATP synthase and thermogenin (UCP1)?
|
- Various transporters (e.g. ANT aka ATP-ADP translocase)
- Other UCP proteins (UCP2-UCP5) have a role in limiting proton gradient |
|
|
What are the roles of UCP2 to UCP5 proteins as we currently understand them?
|
** Not involved in non-shivering thermogenesis
- Do not contribute to basal proton conductance in mito - Expression level << than UCP1 but present in many tissues ** UCP2 limits glucose-stimulated insulin release in pancrease - UCP3 may limit CoASH depletion in mito matrix - UCP2 and UCP3 may limit formation of oxidant stress species in mito - Role of UCP4 and UCP5 still unclear (but mostly in neural tissues) |
|
|
How does UCP2 limit glucose-stimulated insulin release in the pancreas?
|
Normal:
- Pancreatic β-cell senses high glucose (GLUT2) - Metabolism generates ATP/ADP ratio - Shuts ATP-sensing K+ channels, depolarizing membrane - Allows Ca2+ to flow in and stimulate insulin release ** By "wasting" the proton gradient, UCP2 decreases ATP/ADP ratio, limiting all of the above (keeps K channel open; membrane stays polarized; no Ca2+ flow; no insulin secretion) |
|
|
The malate-aspartate shuttle yields how many ATP per glucose compared to the glycerol-phosphate shuttle (for NADH)?
|
- Malate-aspartate shuttle yields 5 ATP
- Glycerol-phosphate shuttle yields 3 ATP |
|
|
Why are fatty acids physiologically important?
|
- Building blocks of phospholipids and glycolipids - components of biological membranes
- Post-translational modifications when attached covalently to proteins - Source of energy - stored in adipose tissue in form of triglycerides - FA derivative - hormones and intracellular messengers |
|
|
Unsaturated FA have up to how many double bonds?
|
6; but always separated by at least one methylene (-CH2-) group)
|
|
|
What configuration of unsaturated FA double bonds in?
|
Usually cis configuration (puts kink in alkyl chain)
|
|
|
How are FA named?
|
- Chain length (# of C atoms) followed by ":"
- # of double bonds - In parentheses, by Δ with superscripts numbering double bonds - C1 is the carboxyl C - Methyl group (-CH3) at end is the ω (omega) C |
|
|
What is the structure of palmitic acid?
|
16:0
(16 C long with no double bonds) |
|
|
What is the structure of palmitoleic acid?
|
16:1 (9)
(16C long with 1 double bond at position 9) |
|
|
What is the structure of stearic acid?
|
18:0
(18 C long with no double bonds) |
|
|
What is the structure of oleic acid?
|
18:1 (9)
(18 C long with 1 double bond at position 9) |
|
|
When the term "oleic" is in the name for a fatty acid what does that mean? Example?
|
- Double bond at position 9
- Palmitoleic = 16:1 (9) - Oleic = 18:1 (9) |
|
|
What are the essential fatty acids?
|
- Linoleic acid= 18:2 (9,12) aka omega-6 FA (b/c last double bond is 6 spots from end)
- Linolenic acid= 18:3 (9,12,15) aka omega-3 FA (b/c last double bond is 3 spots from end) |
|
|
What is the structure of arachidonic acid?
|
20:4 (don't need to know positions)
|
|
|
What is meant by the term "essential fatty acid"?
|
- Polyunsaturated FA (PUFAs) cannot be synthesized in body
- Must be obtained from diet - Humans lack desaturase enzyme required for production |
|
|
What are the sources of omega-3 FA (linolenic acid)?
|
- Vegetable oils
- Nuts and seeds - Shellfish and fish |
|
|
What are the sources of omega-6 FA (linoleic acid)?
|
- Leafy vegetables
- Seeds - Nuts - Grains - Vegetable oils - Meats |
|
|
What is the importance of omega-3 PUFAs?
|
- Eicosanoid synthesis (inflammation) - arachidonic acid (20:4) is a derivative of omega-3 FA
- Endocannabinoids - affects mood, behavior, inflammation - Protects against cardiovascular disease |
|
|
What risk are you at if you have an imbalance of omega-3 and omega-6 fatty acids PUFAs?
|
Increased risk for cardiovascular disease
|
|
|
What are the non-essential fatty acids?
|
- You can survive without them in your diet
- Monounsaturated FAs - PUFAs - Saturated FAs - Trans FAs |
|
|
What are the implications of monounsaturated FAs?
|
Lowers LDL cholesterol
|
|
|
What are the implications of saturated FAs?
|
Raises cholesterol levels
|
|
|
What are the implications of trans FAs?
|
Raise LDL cholesterol and lower HDL cholesterol
|
|
|
How is solubility affected by the characteristics of a FA?
|
- Non-polar hydrocarbon chains cause poor solubility in water
- Longer the chain: lower solubility - More double bonds: increased solubility |
|
|
How does the length of a FA affect its melting point?
|
Longer chains cause melting at higher temperatures
|
|
|
How do double bonds in a FA affect its melting point?
|
Desaturation (double bonds) lowers melting points since "kinks" in chain do not allow for tight packing
|
|
|
What kind of fats have a "waxy" consistency? Why?
|
Fully saturated (12:0 - 24:0) due to tighter packing in membrane
|
|
|
What are the main sources of fatty acids?
|
- Largest: diet
- Second: biosynthesis from small molecules derived from metabolic breakdown of sugars, amino acids, and other FAs |
|
|
Where does FA synthesis take place?
|
Cytosol (although Acetyl-CoA is synthesized in the matrix)
|
|
|
What is the first FA to be synthesized?
|
Palmitic Acid / Palmitate (16:0); all other non-essential FA are made by modifying it
|
|
|
What are the primary substrates for FA synthesis?
|
Acetyl-CoA (ATP, NADPH, CO2/HCO3-)
|
|
|
What is the major source of Acetyl-CoA (for FA synthesis)?
|
Pyruvate Dehydrogenase Complex (PDH) reaction - in mitochondrial matrix
|
|
|
How does the acetyl-CoA synthesized in the matrix get to the cytosol where FA synthesis takes place?
|
- Inner-mitochondrial membrane is impermeable to Acetyl-CoA
- Instead Acetyl-CoA is converted to citrate which is transported across the membranes via the citrate transporter (aka tricarboxylate transporter) - Citrate converted back to oxaloacetate and Acetyl-CoA by ATP-citrate lyase |
|
|
What reaction commits Acetyl-CoA to FA synthesis?
|
- First step:
- Carboxylation of Acetyl-CoA to Malonyl-CoA by "acetyl-CoA carboxylase" - ATP consumed - HCO3- added (requires biotin) |
|
|
What reaction is similar to the one catalyzed by Acetyl-CoA carboxylase (to convert acetyl-CoA to malonyl-CoA for FA synthesis)?
|
Similar to pyruvate carboxylase (first step in gluconeogenesis)
|
|
|
Once malonyl-CoA is synthesized, how is the chain elongated?
|
- Fatty Acid Synthase Complex (FAS)
- Uses Acetyl-CoA, Malonyl-CoA, and 2xNADPH - Repeating 4-step sequence which elongates chain by 2C every time through |
|
|
What are the four steps of the fatty acid synthase complex (FAS)?
|
1. Condensation (releases CO2, replaced by acetyl-CoA)
2. Reduction (uses NADPH to reduce carbonyl to alcohol) 3. Dehydration (release H2O forming double bond) 4. Reduction (uses NADPH to reduce double bond to single bond) |
|
|
What is the benefit of having fatty acid synthase (FAS) complex consist of multiple enzymes?
|
- Direct transfer between sites (no diffusion of intermediates into cytosol, increases efficiency)
- Coordinate transcriptional regulation (one mRNA, many enzyme activities) |
|
|
After Fatty Acid Synthase (FAS) complex generates a fatty acid with a chain length of 16C, what happens?
|
Product, palmitate (16:0) leaves cycle
|
|
|
During FA synthesis, how are the intermediates kept on the FAS complex?
|
- Attached as thioesters to one of two thiol groups
- One attached to an -SH group of a Cys residue - One attached to an -SH group of an acyl carrier protein (ACP) |
|
|
What is the importance of acyl carrier protein (ACP)?
|
ACP serves as a flexible arm, tethering the growing fatty acyl chain to the surface of the Fatty Acid Synthase complex while carrying the reaction intermediates from one enzyme active site to the next
|
|
|
What functional group is attached to the acyl-carrier protein (ACP)? What is its role?
|
- Phosphopantetheine group
- Contains -SH group at end which is esterified to the malonyl groups |
|
|
What happens to set up the first step of FA synthesis (after malonyl-CoA has been synthesized)?
|
- Malonyl/Acetyl-CoA-ACP transferase
- Transfer of acetyl group of acetyl-CoA to ACP followed by transfer of acetyl group to Cys-SH group of β-ketoacyl‐ACP synthase (KS) - Transfer of malonyl group from malonyl-CoA to -SH of ACP - Now acetyl and malonyl groups are activated for chain-lengthening |
|
|
What happens in Step 1 of FAS?
|
- Condensation
- Ketoacyl-ACP synthase (KS) produces 4C unit (acetoacetyl-ACP) - Decarboxylation: CO2 released - releases a lot of free energy driving reaction forward |
|
|
What happens in Step 2 of FAS?
|
- β-ketoacyl-ACP reductase (KR) reduces carbonyl group of acetyoacetyl-ACP to D-β-hydroxybutyryl-ACP (alcohol group)
- Uses NADPH as e- donor |
|
|
What happens in Step 3 of FAS?
|
- Dehydration by β-hydroxyacyl-ACP dehydratase (DH)
- Yields a double bond (from alcohol dehydration) - Forms trans-butenoyl-ACP |
|
|
What happens in Step 4 of FAS?
|
- Reduction of double bond by Enoyl-ACP reductase (ER)
- Forms butyryl-ACP - Uses NADPH as e- donor |
|
|
How many rounds of FAS are required to generate palmitate (16:0)?
|
7 rounds total
(first round gives you 4, 6 more rounds adds 12 C giving 16 C total) |
|
|
How is palmitate (16:0) released from ACP on FAS?
|
Hydrolytic activity of thioesterase (TE) of FAS complex
|
|
|
What is the net reaction of forming palmitate from acetyl-CoA?
|
8 Acetyl-CoA + 7 ATP + 14 NADPH + 14 H+ ----> Palmitate + 8 CoA + 7 ADP + 7 Pi + 14 NADP+ + 6 H2O
|
|
|
Where are fatty acids elongated from palmitate (16:0)?
|
In mitochondria and on cytosolic face of Smooth ER membrane
|
|
|
How is elongation of palmitate in the ER similar to palmitate synthesis?
|
- Donation of two carbons by malonyl-CoA, followed by reduction, dehydration, and reduction to 18C stearoyl-CoA
- NADPH supplies reducing power - Can continue up to C24 in brain otherwise almost exclusively stops at 18:0 |
|
|
Where does the process of desaturating fatty acids take place?
|
ER
|
|
|
What are the precursors for desaturation of FA? What do they produce?
|
- Palmitate (16:0) --> Palmitoleic acid 16:1 (9)
- Stearate (18:0) --> Oleic acid 18:1 (9) |
|
|
What is the committed step in the desaturation of fatty acids?
|
Introduction of cis double bond between C9 and C10; catalyzed by stearoyl-CoA desaturase (mixed-function oxidase)
|
|
|
What is the major precursor of eicosanoid hormones?
|
Arachidonic acid (20:4)
|
|
|
What FA are starting points for the synthesis of arachidonic acid?
|
- Linoleic acid - 18:2 (9,12) = omega-6
- alpha-Linolenic-acid - 18:3 (9,12,15) - These are essential FAs |
|
|
What is the major substrate regulating fatty acid synthesis?
|
Citrate - involved in diverting cellular metabolism from consumption (oxidation) to storage; short-term control
|
|
|
When mitochondrial [ATP] and [acetyl-CoA] increase, what happens as far as regulation of FA synthesis (short-term)?
|
INCREASED FA SYNTHESIS:
- Acetyl-CoA converted to citrate, which is transported out of mito and becomes converted back to cytosolic acetyl-CoA - Citrate is an allosteric signal for activation of acetyl-CoA carboxylase (when phosphorylated) (which converts it to malonyl-CoA for FA synthesis) |
|
|
When mitochondrial [ATP] and [acetyl-CoA] increase, what happens as far as regulation of glycolysis (short-term)?
|
Citrate (synthesized by excess acetyl-CoA) inhibits activity of phosphofructokinase-1 and reduces flow of carbons through glycolysis (there is already enough ATP...time for storage!)
|
|
|
How do palmitoyl-CoA (16:0) and stearoyl-CoA (18:0) affect FA synthesis (short-term)?
|
They are the end products of FA synthesis so they allosterically inhibit acetyl-CoA carboxylase (enzyme that converts acetyl-CoA to malonyl-CoA for FA synthesis)
|
|
|
What is the main regulatory enzyme and rate-limiting step of FA synthesis?
|
Acetyl-CoA carboxylase (converts acetyl-CoA to malonyl-CoA for FA synthesis)
|
|
|
What are the short-term mechanisms by which acetyl-CoA carboxylase is regulated?
|
- Covalent modification (phosphorylation) - triggered by glucagon and epinephrine - inactivates the enzyme and reduces sensitivity to citrate = decrease FA synthesis
- Citrate allosterically stimulates inactivate (phosphorylated) acetyl-CoA carboxylase (increasing activity of FA synthesis) - Citrate has little effect on the active (dephosphorylated enzyme) |
|
|
What substrate of FA synthesis inhibits beta-oxidation of FA?
|
Malonyl-CoA - shuts down beta-oxidation at level of transport system in mitochondrial inner membrane
|
|
|
When is fatty acid biosynthesis maximal?
|
When carbohydrate and energy are plentiful and when fatty acids are scarce
|
|
|
Which enzymes are responsible for phosphorylation and dephosphorylating acetyl-CoA carboxylase? Which is active/inactive?
|
- Inactivated by AMP-activated protein kinase (AMPK) (P = inactive)
- Activated by protein phosphatase 2A (no P = active) |
|
|
What enzyme is considered the "fuel-gauge" of the cell? How does this relate to FA synthesis?
|
- AMPK (AMP activated protein kinase) it is activated by AMP and inhibited by ATP
- If you have lots of AMP you don't want to be synthesizing FA because you need acetyl-CoA for ATP (via TCA cycle) therefore AMPK inactivates acetyl-CoA carboxylase - If you have lots of ATP you want to store acetyl-CoA as FA so enzyme is NOT phoshporylated and is active |
|
|
What are the possible fates of synthesized or ingested FAs?
|
- Incorporation into phospholipid components of membranes during periods of rapid growth or synthesis of new membranes
- Incorporation of TG for storage of metabolic energy and when organism has a plentiful food supply but is not actively growing (FA are shunted into storage fats) |
|
|
What happens to carbohydrates ingested in excess of organism's capacity to store glycogen?
|
Excess is converted to TG and stored in adipose tissues
|
|
|
How are FA neutralized? Why is this important?
|
They are esterified through carboxyl groups to a molecule of glycerol; this facilitates their storage
|
|
|
What are the precursors of both triglycerides and glycerophospholipids?
|
- Glycerol-3P
- Fatty acyl-CoA |
|
|
How is "fatty acyl-CoA" synthesized?
|
Formed from fatty acids by acyl-CoA synthetase; requires ATP and CoASH
|
|
|
What is Step 1 of TG synthesis?
|
- Acylation of two free hydroxyl groups of glycerol-3P by 2 molecules of fatty acyl-CoA
- Yields phosphatidic acid |
|
|
In most cases, the C1 of glycerol is attached to what kind of FA?
|
Saturated
|
|
|
In most cases, the C2 of glycerol is attached to what kind of FA?
|
Unsaturated
|
|
|
What is Step 2 of TG synthesis?
|
- Hydrolysis of phosphatidic acid by phosphatidic acid phosphatase
- Forms 1,2-diacylglycerol |
|
|
What is Step 3 of TG synthesis?
|
Transesterification of diacylglycerol with a third fatty acyl-CoA to form TG
|
|
|
How is triglyceride synthesis regulated?
|
Insulin promotes conversion of carbohydrates to TG
|
|
|
How does having diabetes mellitus affect your TG synthesis?
|
- Unable to use glucose properly (due to failed insulin secretion)
- Also fail to synthesize FA from carbohydrates and AAs - If untreated this leads to increase ketone body formation due to increased fat oxidation |
|
|
What stimulates the release of FA from adipose tissue when FA are needed for energy?
|
Glucagon and epinephrine
|
|
|
How do glucagon and epinephrine affect glycolysis? gluconeogenesis?
|
- Decrease rate of glycolysis
- Increase rate of gluconeogenesis |
|
|
What percentage of FA that are released by lipolysis are actually used as fuel? What happens to the rest of them?
|
~25% used as fuel; other ~75% is re-esterified to form TG again
|
|
|
During starvation, what happens in the "triacylglycerol cycle"?
|
- FA released by lipolysis of TG in adipose
- Some FA enter bloodstream while remainder are re-esterified to TG - FA in blood used for energy (in muscle) or taken up by liver - In liver, FA used for TG synthesis - TG formed in liver transported in blood to adipose tissue - FA is released by lipoprotein lipase and taken up by adipocytes and re-esterified to TG |
|
|
What is the point of the futile TG cycle?
|
Excess capacity of TG cycle may represent an energy reserve in the bloodstream during fasting - one that would be more rapidly mobilized in a "fight or flight" emergency than would stored TG?
|
|
|
What is the function of triglycerides?
|
Storage of energy (more than half the energy requirements of the liver, heart and resting skeletal muscle)
|
|
|
How are simple TGs different from typical TGs?
|
- Simple TGs have the same kind of FA in all 3 positions
- Normal TGs are mixed and contain 2-3 different FAs |
|
|
What kind of foods contain TG with unsaturated FA?
|
Corn oil and olive oil (thus they are liquid at room temperature, because desaturation decreases melting point)
|
|
|
What kind of foods contain TG with saturated FA?
|
Beef fat (white, greasy solid because saturation increases melting point)
|
|
|
Why are TGs good for storage of energy?
|
They are highly concentrated stores of metabolic energy because they are reduced and dehydrated (stored free of water)
|
|
|
How many "calories" are in a g of fat vs a g of carbohydrates or a g of protein?
|
- FAs ~9 kcal/g
- Carbs and protein ~4 kcal/g |
|
|
Why is TG a better stored fuel than glycogen or starches?
|
- Carbon atoms of FA are more reduced than on sugars
- Oxidation of TG yields >2x energy as oxidation of carbohydrates - TG is hydrophobic and unhydrated so don't have to carry extra water weight of hydration as with carbs |
|
|
How do peripheral tissues gain access to fatty acid energy reserves stored in adipocytes?
|
1. TG must be mobilized (degraded to FA and glycerol), released from adipose, and transported to energy-requiring tissues
2. FA must be activated and transported into mito for β-oxidation 3. FA oxidized into acetyl-CoA which can be further processed in TCA cycle |
|
|
In what form are fats ingested? What must happen to them to be absorbed?
|
TG - must be degraded to FAs for absorption across intestinal epithelium
|
|
|
What is the use of bile salts in the intestine?
|
Bile salts are amphipathic lipic molecules synthesized from cholesterol in liver and used to help digestion of TG; act as biological detergents by forming mixed micelles to help emulsify fats
|
|
|
How are triglycerides oriented within the micelle formed with bile salts?
|
TG is oriented with ester bonds towards surface so it is more susceptible to digestion by soluble pancreatic lipase
|
|
|
When is it common for there to be inadequate production of bile salts? What are the consequences?
|
Liver disease or damage (large amounts of fats are excreted in feces = steatorrhea)
|
|
|
Once inside the intestinal mucosa, TG is resynthesized and packaged into what?
|
Chylomicrons = lipoprotein transport particles
|
|
|
What do chylomicrons transport?
|
- TGs
- Fat-soluble vitamins - Cholesterol - Steroid hormones |
|
|
Where are chylomicrons released into?
|
- First into lymph system
- Then flow into blood |
|
|
When chylomicrons get into the blood, what happens to them?
|
They bind membrane-bound lipoprotein lipase at adipose tissue and muscle
|
|
|
What does lipoprotein lipase do when it binds to chylomicrons?
|
Hydrolyzes TG to free FAs and glycerol for transport into the tissues
|
|
|
After TG is broken down by lipoprotein lipase to free FA and glycerol, what happens to them?
|
Resynthesized to TG inside the cell and stored (adipocyte) or utilized/oxidized for energy production (muscle)
|
|
|
Can TG pass through membranes?
|
No, they must be degraded by lipases to free FAs and glycerol (specifically to cross intestinal mucosa and capillary membrane into cells)
|
|
|
How are chylomicron remnants taken up by the liver?
|
Endocytosis
|
|
|
What happens to TGs if the diet contains more FAs than are needed for fuel or as precursors?
|
TG is packed into very low density lipoproteins (VLDL) for transport in blood to adipose tissue (for storage as lipid droplets within adipocytes)
|
|
|
What is used to prevent lipid droplets from being mobilized before they are needed?
|
Perilipin coat covers the lipid droplets
|
|
|
What stimulates lipolysis?
|
Increase in glucagon / insulin ration (similar to glycogen breakdown)
|
|
|
What is the pathway of FA mobilization?
|
1. Epi/glucagon secreted in response to low blood glucose levels, activates adenylyl cyclase to produce cAMP
2. cAMP activates PKA, which phosphorylates perilipin A 3. Phosphorylated perilipin A causes hormone sensitive lipase in cytosol to move to lipid droplet and hydrolyze TG to FA and glycerol (rate-limiting step) 4. FFA pass through adipocyte into blood where they non-covalently bind serum albumin (increases solubility 5. Bound FA carried to tissues needing fuel via bloodstream 6. FA dissociate from serum albumin and move into plasma membrane via transporters to serve as fuel |
|
|
What step of FA mobilization is rate-limiting?
|
Perilipin activation of hormone sensitive lipase which hydrolyzes TG to free FAs and glycerol
|
|
|
How do free FA travel to tissues that need them as fuel?
|
Bind non-covalently to serum albumin (10 FA/monomer), this increases the solubility
|
|
|
What tissues do fatty acids often get taken to on serum albumin?
|
- Skeletal muscle
- Heart muscle - Renal cortex |
|
|
When perilipin is not phosphorylated is it active or inactive?
|
Inactive - must be activated by phosphorylation (via PKA) which is stimulated by glucagon or epinephrine
|
|
|
How is hormone-sensitive lipase affected by Type II (insulin-independent) diabetes?
|
- Aberrant regulation
- Leads frequently to hypertriglyceridemia |
|
|
What happens to the glycerol that is released by the hormone-sensitive lipase?
|
It is absorbed by the liver and phosphorylated, oxidized, and isomerized to glyceraldehyde 3-P (glycolytic and gluconeogenic intermediate)
|
|
|
The enzymes for FA breakdown (β‐oxidation) are found where?
|
In the mitochondrial matrix
|
|
|
How can free FA enter the mito matrix for β‐oxidation?
|
Must be activated via carnitine shuttle
|
|
|
What are the three steps of the carnitine shuttle (used to move free FAs into the mito matrix)?
|
1. FA Esterification to FA-CoA
2. Transesterification to Carnitine followed by transport 3. Transesterification back to CoA |
|
|
What happens during Step 1 of the carnitine shuttle (used to move free FAs into the mito matrix)?
|
- Esterification of FA to Fatty acyl-CoA
- Catalyzed by acyl-CoA synthetase - ATP used to produce acyl-adenylate intermediate - Sulfhydryl group of CoA displaces adenylate (AMP) - Cytosol of OMM - Hydrolysis of 2 P bonds pushes rxn forward |
|
|
What other activation process is similar to the esterification of FA to FA-CoA in step 1 of the Carnitine Shuttle?
|
Aminoacylation of tRNAs during protein synthesis (adenylation by ATP to substrate; replace AMP)
|
|
|
What happens during Step 2 of the carnitine shuttle (used to move free FAs into the mito matrix)?
|
- Transesterification of FA-CoA to FA-carnitine
- FA-carnitine can move through carnitine acyltransferase-1 (CPT1) on OMM - Continues through acyl-carnitine/carnitine transporter (CT) on IMM |
|
|
What product inhibits Carnitine Acyltransferase1 (CPT1), the transporter which helps move FA into the mito matrix (for β‐oxidation)?
|
- Malonyl-CoA is an allosteric inhibitor of CPT1 that is in the liver
- Malonyl-CoA is important for FA synthesis, so if you have lots of FAS happening, you don't want to be breaking down FA |
|
|
What is the rate-limiting step of the carnitine shuttle (used to move free FAs into the mito matrix)?
|
Carnitine-mediated entry (Step 2 of shuttle)
|
|
|
What happens during Step 3 of the carnitine shuttle (used to move free FAs into the mito matrix)?
|
- FA is transferred from carnitine to mitochondrial-CoA
- Catalyzed by carnitine acyltransferase II (CPTII) which is attached to matrix side of IMM - FA-CoA and carnitine released into matrix - Carnitine re-enters intermembrane space via CT (carnitine transporter) |
|
|
What is the significance of having two separate pools of CoA (one in mitochondrial matrix and one in cytosol)?
|
- Mitochondrial CoA used for oxidation degradation of pyruvate (pyruvate dehydrogenase complex), FA, and some AAs
- Cytosolic CoA used for lipid/FA synthesis |
|
|
If there is a deficiency in a component of the "carnitine cycle", what are the implications?
|
Impaired utilization of long-chain FA for energy production (because you are unable to transport FA into mito matrix for β‐oxidation
|
|
|
What are the three stages of β-oxidation of FA?
|
1. Oxidative removal of successive 2C units in form of acetyl-CoA
2. Oxidation of acetyl-CoA to CO2 via TCA cycle 3. Electrons from oxidations in stages 1&2 are passed through electron transport chain to make ATP |
|
|
What are the steps of the first stage of β-oxidation (removal of 2C units in form of acetyl-CoA)?
|
1. Dehydrogenation of fatty acyl-CoA
2. Hydration of trans double bond 3. Second dehydration 4. Thiolytic cleavage |
|
|
What happens during Step 1 of the first stage of β-oxidation (removal of 2C units in form of acetyl-CoA)?
|
- Dehydration of fatty acyl-CoA
- Catalyzed by acyl-CoA dehydrogenase - Forms trans double bond to yield trans-enoyl-CoA - Electrons transferred to FAD-->FADH2, and then to electron-transferring flavoprotein (ETF) for delivery to respiratory chain |
|
|
What are the four different forms of the enzyme acyl-CoA dehydrogenase (used during Step 1 of first stage of β-oxidation)?
|
- Very-long-chain (VLCAD): 12-24C
- Long-chain (LCAD): 12-18C - Medium-chain (MCAD): 4-12C - Short-chain (SCAD): 4-6C |
|
|
What is the location of the four different acyl-CoA dehydrogenases?
|
- VLCAD is bound to inner mitochondrial membrane
- LCAD, MCAD, and SCAD are in the mitochondrial matrix |
|
|
What happens if there is an acyl-CoA dehydrogenase deficiency?
|
- β-oxidation impaired (first enzyme in first stage of β-oxidation)
- MCAD (medium-chain deficiency) most common - Fat accumulates in liver, low blood glucose, vomiting, lethargy, and frequently coma - Best to eat low-fat, high-carb diet |
|
|
What happens during Step 2 of the first stage of β-oxidation (removal of 2C units in form of acetyl-CoA)?
|
- Hydration of trans double bond
- Catalyzed by Enoyl-CoA hydratase - Produces L-β-hydroxyacyl-CoA |
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What happens during Step 3 of the first stage of β-oxidation (removal of 2C units in form of acetyl-CoA)?
|
- Second dehydration catalyzed by L-β-hydroxyacyl-CoA dehydrogenase
- Oxidizes hydroxyl group at C3 and converts to keto group - NADH generated for electron transport chain - Forms β-ketoacyl-CoA |
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What happens during Step 4 of the first stage of β-oxidation (removal of 2C units in form of acetyl-CoA)?
|
- Thiolytic cleavage by acyl-CoA acetyltransferase
- Cleaves β-ketoacyl-CoA to acetyl-CoA and an acyl-CoA (thioester of FA that is shortened by 2C) |
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The enzymes from the last three steps of β-oxidation exist as multiple forms specific to the chain length, where are they located?
|
- Inner mitochondrial membrane bound trifunctional protein contains all three activities w/ long-chain (>12C) specificies for substrates
- Mitochondrial matrix contains monofunctional enzymes for shorter chains, including a thiolase |
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One pass through β-oxidation removes what from the fatty acyl-CoA?
|
- Acetyl-CoA (2C)
- 2 pairs of e- - 4 H+ |
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If you started with palmitate, how many rounds of β-oxidation are required to completely oxidize it? What would be used up?
|
- Seven rounds of β-oxidation
- Palmitate + 7 CoA --> 8 acetyl-CoA - 7 FAD --> 7 FADH2 - 7 NAD+ --> 7 NADH + 7 H+ - 7 H2O |
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What can happen to the acetyl-CoA generated by β-oxidation?
|
- Oxidized to CO2 and H2O through TCA cycle (most tissues, especially skeletal and heart muscle)
- Or used to produce ketone bodies (in liver) |
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Are most of the FAs in TG and phospholipids saturated or unsaturated? What are the implications of this?
|
- Unsaturated - mostly cis configuration
- Need additional enzymes for β-oxidation in order to oxidize cis double bonds (enoyl-CoA hydratase acts only on trans bonds) |
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What additional enzymes are used in the β-oxidation of unsaturated FA?
|
- An extra isomerase (to convert cis to trans isomers)
- A reductase (to convert some two double bond species to correspondign single double bond compound) |
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As an example, how do you oxidize oleate (18:1, 9) by β-oxidation?
|
- Convert to oleoyl-CoA with acyl-CoA synthetase
- Entry into mito matrix via carnitine shuttle (carnitine acyltransferase I (CPT1), carnitine acyltransferase II (CPTII)) - 3 passes of FA oxidation cycle to yield 3 Acetyl-CoA + CoA ester of 12-C unsaturated FA (double bond at C3) - 3-2-enoyl-CoA isomerase converts cis bond to trans (at C2) - 5 more rounds of β-oxidation - Total of 9 acetyl-CoA's produced from 18C oleic acid |
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As an example, how do you oxidize linoleate (18:2, 9/12) by β-oxidation?
|
- Convert to linoleoyl-CoA with acyl-CoA synthetase
- Entry into mito matrix via carnitine shuttle (carnitine acyltransferase I (CPT1), carnitine acyltransferase II (CPTII)) - 3 passes of FA oxidation cycle to yield 3 Acetyl-CoA + CoA ester of 12-C unsaturated FA (double bonds at C3 and C6, both cis) - Dehydrogenation by acyl-CoA dehydrogenase to produce 2,4-dienoyl derivative - 2,4-dienoyl-CoA reductase uses NADPH to make single trans 3,4-double bond - Enoyl-CoA isomerase converts to 10C acyl-CoA with trans double bond at C2 - 4 more rounds of β-oxidation - Total of 9 acetyl-CoA's produced from 18C oleic acid |
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Odd-numbered double bonds are handled by what type of enzymes?
|
Isomerases (to convert to even-numbered double bonds); must be at C2 position (if not must use reductaes and isomerase to move to C2)
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Even-numbered double bonds are handled by what type of enzymes?
|
Reductase and Isomerase to move double bond to C2 position
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What accommodations must be made during β-oxidation if the FA has an odd number of carbons?
|
- Proceeds as normal until left with 5C
- Cleavage of 5C substrate gives one molecule of Acetyl-CoA and 3C molecule propionyl-CoA - Propionyl-CoA enters pathway that yields succinyl-CoA |
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How does the propionyl-CoA that is produced by the oxidation of odd-chained FAs get broken down further?
|
- Propionyl-CoA is carboxylated by propionyl-CoA carboxylase (uses biotin, HCO3- and ATP) to produce D-methylmalonyl-CoA
- Methylmalonyl-CoA Epimerase converts it to L-methylmalonyl-CoA - Methylmalonyl-CoA mutase (requires coenzyme B12: adenosylcobalamin) catalyzes rearrangement to succinyl-CoA (for TCA cycle) |
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Which enzymes are used to break down propionyl-CoA that is produced by the oxidation of odd-chained FAs?
|
- Propionyl-Coa carboxylase (w/ biotin & ATP & HCO3-)
- Methylmalonyl-CoA epimerase - Methylmalonyl-CoA mutase (requires coenzyme B12: adenosylcobalamin) |
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What happens to the succinyl-CoA produced from propionyl-CoA (produced by the oxidation of odd-chained FAs)?
|
Enters the TCA cycle
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When is the B12 vitamin adenosylcobalamin required?
|
For production of succinyl-CoA (enzyme: methyl-malonyl-CoA mutase)
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The breakdown of propionyl-CoA to succinyl-CoA (for TCA cycles) is important for what metabolic processes?
|
- Oxidation of odd-chain FAs
- Degradation of some AAs (isoleucine, valine, and methionine) - Degradation of side chain of cholesterol |
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|
What deficiencies cause propionic acidemia? What happens?
|
- Deficiencies in propionyl-CoA carboxylase and biotin transport
- Encephalopathy - Propionyl-CoA converted to propionic acid (instead of methylmalonyl-CoA) which builds up in bloodstream and damages organs - Special dietary needs which must be managed by dietician |
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|
What deficiencies cause methylmalonic acidemia?
|
- Methylmalonyl-CoA mutase or adenosylcobalamin synthesis (vitamin required for mutase to function)
- Also can be caused by nutritional deficiency in vitamin B12 - Encephalopathy - Build-up of unused methylmalonyl-CoA |
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What are some alternative oxidation mechanisms for fatty acids besides β-oxidation?
|
- ω-oxidation (omega) - assumes a more important role when β-oxidation is defective)
- α-oxidation - used when β-carbon of FA has a methyl group (can't use β-oxidation) |
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|
Which enzymes are used during ω-oxidation of FAs?
|
- Mixed-function oxidase (NADPH, O2)
- Alcohol dehydrogenase (NAD+) - Aldehyde dehydrogenase (NAD+) |
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Where does ω-oxidation of FAs take place?
|
ER of liver and kidneys
|
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Where does α-oxidation of FAs take place?
|
Peroxisomes
|
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When is α-oxidation important?
|
Metabolism of branched chain FA that are present in diet
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What is an example of something in the diet that requires α-oxidation?
|
Phytanic acid (metabolic product of chlorophyll constituent phytol) is abundant in dairy products and ruminant animal fat
|
|
|
What causes Refsum's disease?
|
- Genetic deficiency of a peroxisomal enzyme involved in α-oxidation of phytanic acid
- Accumulate phytanic acid in tissues - Neurological problems - Shortening of 4th toe is helpful for diagnosis - Must restrict dietary intake of dairy and meat products |
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|
What happens with Zellweger syndrome?
|
- Unable to make peroxisomes
- Lack enzymes unique to that organelle - Ex: α-oxidation (used for oxidation of FAs that have methyl groups) - Leads to accumulation of VLCFAs (particularly 26:0) |
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|
What happens with X-linked adrenoleukodystrophy (XALD)?
|
- Fail to oxidize very-long-chain FAs
- Lack of functional transporters for FA in peroxisomal membrane - Affects young boys (<10 years) causing a loss of vision, behavioral disturbances, and early death - Leads to accumulation of VLCFAs (particularly 26:0) |
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When is a diet of Lorenzo's Oil with a diet low in VLCFAs important?
|
When an asymptomatic patient has X-linked adrenoleukodystrophy (XALD) it may delay the onset of symptoms; they typically accumulate VLCFAs (particularly 26:0) due to lack of functional transporter for VLCFAs in peroxisome
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|
What is found in Lorenzo's Oil?
|
- Mixture of oleic acid and erucic acid (prepared from olive oil and rapeseed oil)
- Mixture of FA reduces levels of VLCFAs by competitively inhibiting enzyme that forms VLCFAs |
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|
What are the two potential fates of fatty acyl-CoA in the cytosol?
|
- β-oxidation in mitochondria
- Conversion to TG and phospholipids in cytosol |
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|
What determines whether the FA-CoA is oxidized for converted to TG or phospholipids?
|
- Rate of transfer of long-chain FA-CoA into mito
- 3-step carnitine shuttle (movement of FA groups from cytosol to mito matrix) is the rate-limiting step for FA oxidation |
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|
What factors inhibit β-oxidation of FA?
|
- Malonyl-CoA inhibits carnitine acyltransferase I (inhibits β-ox when liver is supplied with glucose) and is actively making TG in cytosol
- β-hydroxyacyl-CoA dehydrogenase inhibited when [NADH]/[NAD+] - High [acetyl-CoA] inhibits thiolase (enzyme in process of breaking down FA) |
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|
What factors activate β-oxidation of FA?
|
- During fasting, AMPK is activated and phosphorylates acetyl-CoA carboxylase (which decreases malonyl-CoA synthesis)
- Relieves inhibition of fatty acyl-carnitine transport into mito and allows β-ox to replenish supply of ATP |
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|
What can cause acetyl-CoA to be diverted to ketogenesis?
|
- Oxaloacetate is limited if carbohydrates are unavailable (starving/fasting) or improperly utilized (diabetes)
- Oxaloacetate is consumed to form glucose by gluconeogenesis - Acetyl-CoA diverted to ketogenesis |
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|
Where does ketogenesis primarily occur?
|
Liver mitochondrial matrix
|
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|
What three ketone bodies can acetyl-CoA be converted to?
|
- Acetone
- β-hydroxybutyrate - Acetoacetate |
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|
What happens to the ketone bodies?
|
- Acetone - produced in smaller quantities and exhaled
- Acetoacetate/β-hydroxybutarate transported by blood extrahepatic tissues and converted to acetyl-CoA and oxidized in TCA cycle for energy |
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|
What is the pathway of ketogenesis?
|
1. Condensation of 2 acetyl-CoA molecules to form acetoacetyl-CoA (by β-ketothiolase)
2. Acetoacetyl-CoA condenses w/ 3rd acetyl-CoA to form HMG-CoA (by HMG-CoA synthase) 3. Cleavage of HMG-CoA to acetoacetate and acetyl-CoA (by HMG-CoA lyase) 4a. Some acetoacetate reduced to β-hydroxybutarate depending on NADH/NAD+ ratio (consumes NADH in rxn) (by β-hydroxybutarate dehydrogenase) 4b. Acetoacetate can also be converted to acetone releasing CO2 (by acetoacetate decarboxylase) |
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|
Normally, the amount of acetone formed from acetoacetate is negligible, but what can cause it to accumulate?
|
Diabetic ketoacidosis (increased amount of acetone in blood causes some to be expelled in lungs and can be smelled, useful indication of diabetes diagnosis)
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Which tissues can use ketone bodies?
|
- Cardiac and skeletal muscle
- Brain |
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|
How do ketone bodies get converted back to acetyl-CoA for energy usage (TCA cycle)?
|
- Ketone bodies (acetoacetate) activated by succinyl-CoA to acetoacetyl-CoA (by β-ketoacyl-CoA transferase)
- A thiolase then cleaves acetoacetyl-CoA into 2 acetyl-CoA molecules |
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|
Under normal dietary conditions, hepatic production of ketone bodies is approximately how much?
|
Minimal (<0.2 mM)
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|
How high can ketone bodies get when under food deprivation?
|
3-5 mM
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|
In diabetic ketoacidosis, how high can the amount of ketone bodies in the blood be?
|
Up to 20 mM
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|
In untreated diabetes, when insulin levels are insufficient, tissues can't take up glucose, therefore what happens?
|
- Levels of malonyl-CoA fall (starting material for FA synthesis)
- Less inhibition of carnitine acyltransferase (important for FA oxidation, so increased) - FA enter mito to be degraded to acetyl-CoA (which can't pass through TCA cycle because intermediates are being used for gluconeogenesis) - Accumulation of acetyl-CoA leads to formation of ketone bodies beyond capacity of extrahepatic tissues to oxidize them - Increased ketone bodies lowers blood pH causing acidosis - Lipid droplets accumulate in cells |
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|
What is ketosis?
|
Extremely high blood and urine levels of ketone bodies; can cause acidosis (low blood pH)
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|
What are amino acids primarily used for?
|
- New protein synthesis (80%)
- Converted to other important molecules (AAs, energy carrying molecules, hormones, NTs, nucleic acids, and catecholamines) (20%) |
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|
How much protein is degraded per day on average? Where does this protein come from?
|
- ~400g/day of body protein
- ~100g/day of dietary protein |
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|
What are the two intracellular protein degradation systems?
|
- Lysosomal system: non-specific
- Ubiquitin-Proteasome system: specific (abnormal proteins and with short half-lives) |
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|
What kind of enzymes degrade dietary proteins in the stomach and small intestine?
|
- Endoproteases: cleave specific peptide bonds
- Exoproteases: cleave from N and C terminal ends |
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|
What do parietal (oxyntic) cells in the stomach do?
|
- Release HCl to acidify stomach
- Denatures dietary proteins |
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|
What do the cheif (peptic) cells in the stomach do?
|
- Release pepsinogen (inactive precursor/zymogen)
- Activated by low pH (~2) to form pepsin (cleavage of N-terminal peptide) - Further activates other pepsinogen molecules - Inactivated in intestine (less acidic) |
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|
What is the role of pepsin? Where does it come from?
|
- Cleaves proteins at peptide bond before large hydrophobic AAs
- Released from chief (peptic) cells in stomach |
|
|
What happens in GERD (gastroesophageal reflux disease)?
|
- Esophagus is chronically exposed to HCl and pepsin
- Induces degradation of epithelial layer of esophagus - Affects 25-40% of pop. |
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|
What do the pancreatic acinar cells do?
|
- Secretes bicarbonate; increases pH to ~6.0-6.7 (this inactivates pepsin)
- Also synthesizes and secretes trypsinogen, chymotrypsinogen, and proelastase |
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|
How do the zymogens released by the pancreatic acinar cells become active?
|
- Trypsinogen activated to trypsin by enteropeptidase present on intestinal epithelial cells
- Trypsin activates proelastase to elastase and chymotrypsinogen to chymotrypsin |
|
|
What does trypsin cleave?
|
- After basic amino acids (Lys, Arg)
- Also activates the endopeptidases proelastase and chymotrypsinogen - Activates the exopeptidase procarboxypeptidase to carboxypeptidase |
|
|
What does elastase cleave?
|
After small AAs (Ala and Gly)
|
|
|
What does chymotrypsin cleave?
|
- After cyclic aromatic AAs (Phe, Trp, and Tyr)
- After branched chain AAs (Ile, Leu, and Val) |
|
|
What kind of cells synthesize and secrete carboxypeptidases? Aminopeptidases?
|
- Carboxypeptidases from α-cells of the pancreas - activated by trypsin
- Aminopeptidases from intestinal epithelial cells - in active form |
|
|
How do amino acids get absorbed in the intestine?
|
Intestinal epithelial cells have sodium co-transporters specific for different types of AAs
|
|
|
What causes "cystinuria"? Symptoms?
|
- Deficiency of basic amino acid transporter (Lys, Arg, Cys, Cys-Cys)
- Leads to formation of kidney stones containing cystine (Cys-Cys) - Caused by abnormal reabsorption of cystine in renal tubules and insolubility of cystine at pH of urine (5-7) - Lys and Arg are excreted at high levels |
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|
What causes Hartnup disease? Symptoms?
|
- Deficiency in neutral amino acid transporter (Phe, Tyr, Met, Val, Leu, Ile, Trp)
- Cerebellar ataxia and pellagra-like symptoms (dermatitis) - Low tryptophan absorption - Deficiency in niacin derivatives NADH and NADPH - ~50% of niacin requirement is from Trp |
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|
How do dietary AAs get from intestine to liver?
|
Portal vein
|
|
|
Which AAs, when in excess, can be used as a source of energy in tissues other than liver (~10%)?
|
Valine, Leucine, Isoleucine
|
|
|
What's the difference between "non-essential", "conditionally essential" and "essential AAs?
|
- Non-essential and conditionally essential AAs can be synthesized
- Conditionally essential AAs are only required from diet under growth or disease conditions - Essential AAs are required from diet (cannot be synthesized) |
|
|
How much new protein is synthesized per day using AAs?
|
~400 g/day
|
|
|
What proteins are typically synthesized on a daily basis?
|
- Cell division
- Circadian rhythm - Energy metabolism - Gene expression |
|
|
If AAs are not needed for protein synthesis or for production of AA derivatives, what happens to them?
|
They are degraded for energy production
|
|
|
What happens to ammonia that is generated from amino acid degradation?
|
- Free ammonia
- Transferred to α-ketoglutarate to form glutamate (by aminotransferase w/ PLP) |
|
|
What transport AAs can carry ammonia to the liver for urea synthesis?
|
- Glutamine
- Alanine - Serine |
|
|
What happens to the carbon backbones of AAs that are degraded?
|
Degraded to molecules that can be used in synthesis of lipids and glucose
|
|
|
In the fed state, how much does AA degradation contribute to energy needs?
|
~10%
|
|
|
In the early fasting state, how much does AA degradation contribute to energy needs?
|
~33%
|
|
|
What are the two most common aminotransferases?
|
- Alanine aminotransferase (ALT) - higher in liver
- Aspartate aminotransferase (AST) - same in most cells |
|
|
How much alanine and aspartate aminotransferase is there usually?
|
- Usually very low amounts
- Enzyme is released when organ is damaged - Indicates liver disease when both are high - High AST alone indicates damage to other organs |
|
|
What enzymes release free ammonia?
|
- Dehydratases release it from serine and threonine (hydrolytic rxn)
- Lyases release it from AAs by directly splitting bonds |
|
|
What source other than AAs can remove ammonia?
|
Deaminases remove ammonia from purines and pyrimidines
|
|
|
Where are glutamine, alanine and serine used for ammonia transport?
|
- Glutamine - most tissues
- Alanine - muscle, kidney, and intestine - Serine - kidney |
|
|
How is glutamine synthesized from glutamate?
|
- ATP molecule used to activate glutamate w/ glutamine synthetase
- Ammonia adds/displaces Pi to make glutamine |
|
|
What four enzymes are used in the urea cycle?
|
1. Ornithine Transcarbamoylase
2. Argininosuccinate Synthetase 3. Argininosuccinase Lyase 4. Arginase |
|
|
What substrates / intermediates / products are found in the Urea cycle?
|
1. Ornithine (+ Carbamoyl Phosphate)
2. Citrulline (+ ATP + Aspartate) 3. Argininosuccinate 4. Arginine (- Fumarate) ---> Urea released from arginine (leaving ornithine) |
|
|
What are the four steps of the Urea cycle?
|
1. Ornithine + Carbamoyl-P combine by ornithine transcarbamoylase to form citrulline (releasing Pi)
2. Citrulline activated w/ ATP (PPi released) and Aspartate added to displace AMP via argininosuccinate synthetase forming argininosuccinate 3. Argininosuccinase lyase cleaves into arginine and fumarate 4. Arginine converted by arginase to ornithine (releasing UREA) |
|
|
What is the structure of Urea?
|
Carbonyl in center with two NH2 groups
|
|
|
Where does the urea cycle primarily take place?
|
Liver
|
|
|
Ammonia that is brought into the mitochondrial matrix by glutamate and glutamine is converted to what for the urea cycle?
|
- Converted to carbamoyl phosphate by carbamoyl phosphate synthetase 1
- Adds CO2 (from HCO3-) - Adds Pi (from 2 molecules of ATP |
|
|
What regulates the synthesis of carbamoyl phosphate?
|
- N-acetylglutamate (Carbamoyl phosphate synthetase I has very little activity in the absence of this regulator)
- N-acetylglutmate synthesized by N-acetylglutamate synthase which is activated by Arginine |
|
|
What controls the urea cycle?
|
Levels of carbamoyl phosphate (made from ammonia and bicarb)
|
|
|
Which stages of the urea cycle take place in the matrix and which take place in the cytosol?
|
- Matrix = step 1 (ornithine transcarbamoylase)
- Cytosol: steps 2, 3, and 4 - Therefore need ornithine transporter INTO matrix and citrulline transporter OUT of matrix |
|
|
How many ATP are used for the Urea Cycle?
|
3: 2 for conversion of ammonia to carbamoyl phosphate and 1 for activation of citrulline
|
|
|
What is the overall reaction of the urea cycle (including carbamoyl phosphate synthesis)?
|
NH4+ + HCO3- + 3 ATP + H2O + Aspartate --> Urea + 2 ADP + AMP + 2Pi + PPi + Fumarate
|
|
|
What happens to the fumarate released during the urea cycle?
|
Converted in cytoplasm to malate by fumarase; both fumarate and malate cross mitochondrial membrane and are used by TCA cycle
|
|
|
How are the Urea cycle and TCA cycle linked?
|
- Fumarate (and malate) released by Urea cycle from argininosuccinate enter TCA cycle
- Aspartate generated during TCA cycle combined with citrulline in urea cycle to form argininosuccinate |
|
|
What can amino acids be degraded to?
|
- Pyruvate
- Acetyl-CoA - Citric Acid intermediates |
|
|
Which amino acids are ketogenic (form ketone bodies)?
|
Leu, Lys, Phe, Trp, Tyr, Ile, Thr
|
|
|
Which amino acids are glucogenic?
|
Ala, Cys, Gly, Ser, Thr, Trp, Asp, Asn, Arg, Glu, His, Pro, Gln, Ile, Met, Thr, Val, Phe, Tyr
|
