PDH and TCA cycle Flashcards
Does any type of substrate phosphorylation occur in the TCA cycle?
yes, one GTP is made
What is the overall goal of the TCA cycle?
Strip electrons from pyruvate and oxidize it completely to 3 CO2 molecules
How are electons recovered from the TCA cycle?
NADH an FADH2
How does the handling of pyruvate change as the cell moves from anaerobic to aerobic condition?
Anaerobic
- Pyruvate –> lactate
Aerobic
- Pyruvate –> 3 CO2
Where does the TCA cycle take place?
- In the matrix of the mitochondria
T or F: all proteins involved in the TCA cycle are membrane bound.
False, the only membrane bound protein is succinate dehydrogenase
How does pyruvate get into the intermembrane space of the mitochondria and then into the matrix?
- it passes through a porin in outer membrane
- uses carrier to get through the inner membrane
What 5 ways can the cell get Acetyl CoA?
- Glycolysis
- Amino Acid Oxidation
- Beta Oxidation
- Ethanol oxidation
- Ketone bodies
T or F: a mutation in the mitochondrial genome could prevent PDH complex transcription.
False, the PDH complex is coded for by the cell nucleus
What enzyme would be rendered dysfunctional if TPP its cofactor was removed?
- Subunit E1 of the PDH complex (aka pyruvate decarboxylase)
- Subunit E1 of alpha ketoglutarate dehydrogenase
Which subunit of PDH complex requires NAD+ and FAD?
Subunit E3
What is the cofactor for E2 in the PDH complex and what does it do?
- Lipoic acid (contains oxidized disulfide bonds forming a 5 membered ring.
- Reacts with carbanion intermediate created by E1 to make a thioester
- Moves to E2 where the acetate is taken from the lipoic acid and a new thioester is formed with CoA (aka Acetyl-CoA)
- Lipoic acid is released in reduced form (but must be reoxidized for cycle to continue)
T or F: the E3 subunit creates products that are used in the TCA cycle?
False, the job of the E3 subunit is to reoxidize the lipoic acid so that the E2 subunit can keep making acetyl CoA
- Also, NADH is make from E3 which can be used in OxPhos
What is the first irreversible step in the TCA cycle, and what is the driving force for this reaction?
- Condensation of OAA and Acetyl CoA to produce citrate
- Catalyzed by Citrate Synthase
- Hydrolysis of CoA drives the reaction
What does arsenite inhibit?
E2 of PDH
Describe the structural changes in citrate synthetase as well as the purpose of these changes.
- OAA binds, this opens up Acetyl-CoA binding site
- Acetyle-CoA binds
- Citroyl-CoA forms inducing another structural change that allows for hydrolysis
-The purpose of these steps is to protect against wasteful hydrolysis of acetyle-CoA
Explain how acetyl CoA from the mitochondria can get to the cytosol.
- it must be converted citrate first by citrate synthase, because Acetyl-CoA has no mito. transporters
- Citrate can be exported from the mito.
- ATP citrate lyase cleaves citrate to making OAA and acetyl-CoA by adding CoA
What two cycles are combined to make the TCA cycle and what is the linking enzyme between these two cycles?
- 1st pt of TCA = alpha-ketoglutarate to make different amino acids
- 2nd pt of TCA in backwards direction leads to succinyl CoA synthesis, used to make heme
- alpha-ketoglutarate dehydrogenase is the linking enzyme
T or F: alpha ketoglutarate dehydrogenase is related to the PDH complex.
True, The E1 and E2 subunits are extremely similar and the E3 subunit is exactly the same in both
What enzymes in the TCA cycle are responsible for making NADH or FADH2?
- Isocitrate Dehydrogenase
- alpha-ketoglutarate dehydrogenase
- Succinate Dehydrogenase (FADH2)
- Malate Dehydrogenase
What two enzymes are responsible for oxidative decarboxylation of citrate, aka release of CO2?
- Isocitrate Dehydrogenase
5. Alpha-ketoglutarate Dehydrogenase
T or F: even if you have all TCA enzymes and lots of Acetyl CoA the cycle will not run unless a small amount of one of the intermediates is present.
True
What prevents fats from being made into sugars?
- The two oxidative decarboxylations in the TCA cycle
- Two acetyl CoA carbons are added but two OAA carbons leave with each cycle leaving no carbons the can be used in biosynthesis
What enzyme in the TCA cycle does substrate level phosphorylation?
Succinyl CoA synthetase makes GTP
