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60 Cards in this Set

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what is the main function of the TCA cycle?
allows oxidation of metabolic intermediates to CO2 and H20 in a manner that allows the energy released by the oxidation to be captured in NADH, FADH2, and GTP
main substrate consumed by the TCA cycle?
Acetyl CoA from Pyruvate
how many carbons are released as C02 in one full turn of the TCA cycle?
2
what does it mean for Citrate to be prochiral?
enzymes CAN tell the two different sides even though a mirror could not distinguish the two sides of a molecule
where do the carbons that are released as CO2 come from?
OAA
Citrate Synthase
Acetyl CoA + OAA -> Citrate
where does cleavage of thiolester bond (high energy) occur?
Citrate Synthase step
what enzyme can distinguish the un-equivalent groups of Citrate?
Aconitase
Aconitase
catalyzes DEHYRDATIION of Citrate to Cis-ACONITATE......also REHYDRATES this molecule back to ISOCITRATE
what is the purpose of Aconitase Dehydrating and then Rehydrating the Citrate molecule?
move the OH group of Citrate to a position where it can be oxidized to a ketone
active site of Aconitase
Iron-Sulfur Center
Purpose of Iron Sulfur Centers
help position substrates in the active site
Isocitrate Dehydrogenase converts Isocitrate to.....?
alpha-ketoglutarate....(2 steps..first oxidized to ketone)
First step where NADH is released?
Isocitrate Dehydrogenase (know because oxidation of alcohol to ketone has occured)
where is first C02 lost and why?
Isocitrate step- unstable B- Keto acid
alpha-ketoglutarate step converts alpha ketoglutarate to ? Same as what other mechanism?
Succinyl CoA
Pyruvate Dehydrogenase Complex mechanism
key differences in alpha ketoglutarate stop and Pyruvate Dehydrogenase Complex reaction?
different substrate (alpha ketoglutarate)
NOT regulated by phosphorylation
cofactors used by Alpha Ketoglutarate Dehydrogenase
TPP, lipoic acid, FAD
where is the second high energy thioester bond found?
Succinyl CoA
Succinyl CoA Synthetase
harvest energy of Succinyl CoA as GTP by converting it to Succinate
where is substrate level phosphorylation in the TCA cycle?
Succinyl CoA Synthetase
where is plane of symmetry present and carbons can no longer be tracked?
Succinate
can be sure to say that in Succinate, one carboxylate and one methyl came from____?
Acetyl CoA
After what molecule are the steps just to get back to OAA?
After Succinate
Fumarate
Malate
OAA
Succinate Dehydrogenase
oxidizes Succinate to Fumarate
what is released as Succinate is oxidized to Fumarate?
FADH2
what is the one enzyme that is not free floating in matrix, but it embedded in the Inner Mitochondrial Membrane?
Succinate Dehydrogenase
What two enzymes contain Iron Sulfur Centers?
Aconitase
Succinate Dehydrogenase
What happens in Fumarase step
Water is added to convert fumarate to malate
which enzyme catalyzes step with an unfavorable equillibrium?
Malate Dehydrogenase
where is third NADP released in TCA cycle?
Malate Dehydrogenase step
how does Malate Dehydrogenase work even though has unfavorable equillibrium?
OAA is depleted in TCA cycle so it drives this reaction forward.....In addition, NAD concentrations in the cell are much greater than NADH
94% of energy is stored in TCA cycle...where is all of the energy stored?
NADH, FADH2 and GTP
where are the CO2 producing carbons of the TCA cycle? ones that come off?
C1 and C4 of OAA
after how many turns of the TCA cycle will the Carbonyl C of Acetyl CoA be removed?
2 turns
what are the key regulators of the TCA cycle?
NAD/NADH, ATP/ADP, and Succinyl CoA
What are the three major enzyme sites of regulation in the TCA Cycle
1) Citrate Synthase
2) Isocitrate Dehydrogenase
3) alpha-Ketoglutarate Dehydrogenase
What is Citrate Synthase inhibited by?
ATP, NADH and Succinyl CoA
what makes Isocitrate more effective at lower concentrations?
ADP
what negatively modulates Isocitrate Dehydrogenase? positively?
negatively- ATP, NADH

positively- ADP, NAD
what negatively modulates alpha Ketoglutarate Dehydrogenae?
Succinly CoA and NADH (much like Pyruvate Dehydrogenase Complex)
4 Sources of Acetyl CoA
1) Pyruvate Dehydrogenase Complex
2) Fatty Acid Oxidation
3) Amino Acids- Isoleucine, Leucine, and Tryptophan
Amino Acids that can yield Acetyl CoA
Leucine, Isoleucine, and Tryptophan
steps in producing acetyl CoA from ethanol
ethanol- acetaldehyde- acetic acid- acetyl CoA
Three enzymes required for the production of acetyl CoA from ethanol?
1) Alcohol Dehydrogenase
2) Aldehyde Dehydrogenase
3) Acetyl CoA Synthetase
what can inhibit gluconeogenesis?
Ethanol
How can gluconeogenesis use intermediates from the TCA cycle?
OAA (actually must be converted to malate by reversal of the malate dehydrogenase reaction or else to aspartate before it can leave the matrix to go to the cytosol)
How can lipids use intermediates of the TCA cycle?
Citrate goes out into the cytosol and is converted to Acetyl CoA
Enzyme that converts Citrate to Acetyl CoA in the cytosol?
Citrate Lyase
How can amino acid biosynthesis use intermediates of the TCA cycle?
OAA ---> Aspartate
a-ketoglutarate---> Glutamate
What does the synthesis of porphyrin (heme) require?
Succinyl CoA
reactions that REPLENISH the intermediates of the TCA cycle are called?
ANAPLEROTIC REACTIONS
The main anaplerotic reaction?
Pyruvate Carboxylase (Pyruvate--> OAA)
what does Pyruvate Carboxylase require as a cofactor?
Biotin
what activates Pyruvate Carboxylase?
the accumulation of Acetyl CoA
If Acetyl CoA accumulates due to the lack of OAA, then ....
more OAA is formed
If Acetyl CoA accumulates for another reason besides depletion of OAA....
OAA is still formed, but it is converted to Malate or Aspartate for GLUCONEOGENESIS
Two fates of Pyruvate (list enzymes that coincide with both steps):
1)Pyruvate Dehydrogenase Complex: can be converted to Acetyl CoA to go into Citric Acid Cycle to be used for energy
2) Pyruvate Carboxylase: can be converted to OAA, which is converted to Malate or Aspartate to be used in GLUCONEOGENESIS to make glucose
How can amino acids and fats replenish intermediates of the TCA cycle?
can be degraded to intermediates of the cycle... (fats)- odd chain and branched fatty acids are degraded to propionyl-CoA which is metabolized to Succinyl- CoA
How does the purine nucleotide Cycle contribute to intermediates of the TCA cycle?
conversion of Aspartate--> Fumarate