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24 Cards in this Set
- Front
- Back
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1. Name the subcellular locations of glycolysis, the citric acid cycle, & oxidative phosphorylation
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Glycolysis = cytoplasm
Citric acid cycle = mitochondria Ox Phos = IMM |
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2. ID common monosaccharides, disaccharides & polysaccharides. Explain why ingested disacc/polysaccs must be broken down to monosaccs & describe how this is accomplished.
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Monosaccs = glucose, galactose, mannose, fructose, ribose
Disaccs = sucrose (glu + fru), lactose (glu + gal), maltose (glu + glu) Polysaccs = starch, glycogen, fiber Breakdown of disaccharides and polysaccharides occurs outside of the cell. It has to be accomplished by enzymes that are released from cells out into the lumen of the GI tract. How? enzs break glycosidic bond btw monosaccs Why? b/c we cannot absorb/use energy from complex sugars unless they are fully broken down into their component parts. |
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5. Describe the fx of the enzs glucokinase & hexokinase. Compare tissue distributions, affinity for glucose, & regulation.
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Both GK & HK converts glu to G6P
GK (in liver & pancreas) has low affinity to glu; upregulated by Insulin. HK (not in liver, in pancreas and many other tissues) has high affinity to glu; inhibited by G6P |
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6. Explain why the NAD used during glycolysis must be regenerated. Describe how this is accomplished under aerobic & anaerobic conditions & in cells w/o mitochondria.
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The cell's supply of NAD is finite, so cytoplasmic NAD must be regenerated from NADH in order for glycolysis to continue.
Under aerobic conditions (w/mitochondria & oxygen), we can use the malate shuttle. Under anaerobic conditions (w/o oxygen and/or mitochondria), we must use lactate dehydrogenase (LDH) to regenerate NAD in the cytosol. |
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6b. Explain how the malate shuttle works.
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(1) Transfer the electrons from cytoplasmic NADH to oxaloacetate, reducing it to malate and leaving us with NAD. Both steps are catalyzed by the same enzyme, malate dehydrogenase.
(2) Malate (with the transferred electrons) is transported into mitochondrion b/c IMM has a carrier protein for malate. (3) The same enzyme (malate dehydrogenase) is present in the matrix as well. It regenerates OAA from malate using the electrons and transfers them to NAD in the matrix to yield NADH. |
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6c. Why do we need the malate shuttle to regenerate NAD in the cytoplasm?
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The malate shuttle system is required because the inner membrane is impermeable to NADH. Instead, malate carries the reducing equivalents across the membrane.
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6d. How do we generate cytosolic NAD in RBCs and skeletal muscle cells? Why?
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RBCs lack mitochodria & therefore lack the tools for ox phos.
In rapidly contracting muscle cells, the need for ATP formation may exceed the rate at which oxygen can be taken up and utilized in ox phos. In each case, pyruvate is converted to lactate by lactate dehydrogenase. Reducing equivalents from NADH are transferred to pyruvate, regenerating NAD in the cytosol. LDH activity is not highly regulated. The direction of its reaction is entirely dependent on the concentration of intermediates |
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7. Explain why pyruvate kinase deficiency can lead to hemolytic anemia.
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RBCs need glucose for energy thru glycolysis.
If no pyruvate kinase, no glycolysis & no ATP for RBCs RBCs w/o ATP → lyse → anemia |
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8. Name 2 enz defects that could result in elevated levels of lactate in the serum
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Pyruvate dehydrogenase complex - if defect, pyruvate accumulates & since lactate dehydrogenase is widely expressed, lactate will accumulate
Gluconeogenesis enz(F1,6BP/ G6P) - if defective, no (pyr → glucose) rxn, so pyr can accumulate → lactate Ox-Phos enz (ATP synthase/NADH dehydrogenase complex/ cytochrome oxidase complex) - if defect, reduced ox-phos, ↑NADH, ↓TCA cycle → pyr accumulate →lactate Pyruvate symporter- if defect, pyr can’t get in mito, accumulate in cytosol →lactate |
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9. Describe the structure of a mitochondrion. Discuss the permeability of the outer and inner membranes to polar molecules like NADH & pyruvate.
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-Bilayer membrane: outer mem permeable to <5000 D; inner mem permeable to molecs & ions w/transporters
-invaginated inner mem- ↑surface area for ox-phos, transport, malate shuttle etc. |
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Explain oxidative phosphorylation.
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Oxidative phosphorylation (ox phos), is a process where electrons carried by NADH and FADH2 are ultimately transferred to O2 and used to drive the phosphorylation of ADP to synthesize ATP.
Ox Phos performed through the coupled operation of 2 components of the IMM: (1) ETC, which is dependent on O2, and (2) ATP synthase. |
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10. Describe the fx of the pyruvate dehydrogenase complex. Name the coenz used by the complex. Explain regulation.
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- Once in the mitoc, pyr converted → acetyl CoA for TCA cycle
- uses 3 enz & 5 coenz- FAD, NAD, thiamin pyrophosphate, lipoic acid, CoA - activity regulated by conc of ATP, NADH, & acetyl CoA. All 3 inhibit the complex by inhibiting the first enzyme pyruvate decarboxylase. Occurs when cellular energy needs are met (ATP pools are filled, NADH accumulates, or acetyl CoA produced from other fuels) |
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10b. Name the coenzymes used by pyruvate dehydrogenase and what vitamins are responsible for their production.
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5 Conezymes:
1. NAD (from niacin) 2. FAD (from riboflavin) 3. thiamin pyrophosphate (from thiamine) 4. lipoic acid (from pentathenic acid, B5) 5. coenzyme A (from pentathenic acid, B5) |
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11a. Dexcribe the operation of the e- transport chain & ATP synthase, explain how they’re functionally coupled.
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Operation is ox phos --> (1) oxidative part refers to the fact that we are oxidizing NADH and FADH2 and (2) phosphorylation part is referring to the fact that we are directly phosphorylating ADP in order to make ATP.
Ox Phos process takes place at the IMM. We are essentially taking the electrons from NADH and FADH2 and handing them off from one protein to another during ETC until we reach the last protein in the chain, which then hands off the electrons to oxygen and yields water. NADH → NADH dehydrogenase → e- shuttled by CYTOCHROME complexes causing H+ to move out of mito matrix and into IMM space →1/2 O2 is final e- acceptor →H2O 10 H+ moved into IMM space → ATP synthase → ADP converted to ATP Coupled rxns: (1) ATP synthase requires H+ to activate enz as moves from intermem space to matrix down [ ] gradient (favorable rxn) and (2) [ ] gradient is formed by e- movement that draws H+ to intermem space against [ ] gradient (unfavorable) |
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11b. Explain how oxidative phosphorylation is regulated by ADP levels, how regulation of ox-phos regulates TCA & glycolysis.
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Regulation: high ADP levels activate ox-phos (because draws more H+ down gradient & into mito), becomes easier for H+ to move to IMM space as e- are shuttled across the chain and more NADH is used; requires (and regulated by) oxygen
as [NADH] ↓→ activates TCA isocitrate dehydrogenase & α-ketogluarate dehydrogenase |
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12. Predict the effect on ox-phos from inhibitors of e- transport, ATP synthase, uncouplers of ox-phos.
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e- transport inhibitors→ ↓ H+ drawn to intermem space→↓ [H+] gradient→↓ ATP synthesis
ATP synthase inhibitors→ ↓ H+ drawn to matrix→buildup + charge in intermem space→e- transport ↓ Ox-phos uncouplers→e- transport detached from ATP synthase→ buildup + charge in intermem space → ↓ox-phos |
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What drives the ETC?
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ETC uses the free energy available from reoxidation of NADH and FADH2 to create a transmembrane proton gradient.
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What drives ATP synthase?
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ATP synthase uses the energy stored in the transmembrane proton gradient (made by ETC) to form ATP from ADP and Pi.
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13. Describe the overall design of the pentose phosphate pathway, ID regulated step, name products.
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Pentose phosphate pathway is an alternative pathway to oxidize glucose.
It has two major fxs: (1) to produce NADPH, and (2) to generate 5-carbon sugars for nucleotide synthesis. Liver, adipose tissue, RBCs, and lactating mammary glands are all important pentose phosphate pathway locations. Has 2 parts: (1) oxidative part, and (2) non-oxidative part. * Oxidative part converts G6P to ribose-5-phosphate and produces 2 NADPH. * Most of the steps are thermodynamically irreversible, thus ensuring cell maintains high NADPH/NADP ratio. * If more NADPH is needed, excess ribose 5-phosphate enters the second, non-oxidative part of pathway, and is converted to compounds that re-enter glycolysis. Regulation: thermodynamically irreversible oxidation steps Products: NADPH, ribose 5-phosphate→ glycolysis |
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14. Explain why G6P dehydrogenase deficiency can lead to hemolytic anemia, name 2 triggers of this disease if deficient.
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-G6PD deficiency → increase oxidative damage to RBCs → RBC destruction (hemolysis) leads to anemia
Triggers: infection, use of certain drugs, & consumption of fava beans. |
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Name examples of monosaccharides.
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Glucose (dextrose),
Galactose, Fructose (levulose), Xylose, Ribose |
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Name examples of disaccharides & state their monosaccharide subunits.
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Sucrose (glucose + fructose),
Lactose (glucose + galactose), Maltose (glucose + glucose). |
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Discuss the fx of α-ketoglutarate dehydrogenase.
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The α-ketoglutarate dehydrogenase is multienzymatic complex made up of three different types of enzymes, responsible for the conversion of α-ketoglutarate in to succinyl CoA.
This is an important step in the citric acid cycle as it can be used to regulate energy production. α-ketoglutarate is a gateway for amino acids to enter the citric acid cycle and produce energy; this is a reversable reaction, so sugars which enter the cycle can leave it to make amino acids. |
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What is the fx of pyruvate kinase?
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Pyruvate kinase is an enzyme involved in glycolysis. It catalyzes the transfer of a phosphate group from phosphoenolpyruvate (PEP) to ADP, yielding one molecule of pyruvate and one molecule of ATP.
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