Lecture 10 - TCA cycle Flashcards
What does TCA stand for?
tricarboxylic acid
What are the other names for the TCA cycle?
Citric acid cycle; Krebs cycle
What is the first step? (i.e., what happens to pyruvate?
it’s converted to acetyl coenzyme A by oxidative decarboxylation
What is decarboxylation?
a chemical reaction that removes a carboxyl group and releases carbon dioxide
What begins the TCA cycle?
the entry of acetate as acetyl CoA
What are the products of the TCA cycle?
CO2, ATP, NADH and FADH2
Acetyl CoA -> 3 NADH + FADH2 + ATP + 2 CO2
What were the 3 important enzymes mentioned?
CAC-3: isocitrate dehydrogenase
CAC-4: alpha-ketoglutarate dehydrogenase
CAC-6: succinate dehydrogenase
What enzyme is inhibited by its products? What are the products? What else inhibits it?
oxoglutarate/ alpha-ketoglutarate dehydrogenase
succinyl CoA and NADH
high energy charge in cell is also inhibitive
What are the allosteric activators of oxoglutarate dehydrogenase?
ADP and calcium ions
What is an allosteric regulator?
a substance that binds to a site on an enzyme distinct from the active site
True or false: succinate dehydrogenase is not the only enzyme that participates in both the citric acid cycle and the electron transport chain
false
What else does the TCA cycle play an important role in?
the catabolism of proteins and lipids
Catabolism of TAG molecules
begins with their hydrolysis to glycerol and free fatty acids
Fatty acids and the TCA cycle
fatty acids are linked to coenzyme A to form fatty acyl CoAs, which are then degraded by beta oxidation, a catabolic process that generates acetyl CoA and the reduced coenzymes NADH and FADH2
Proteins and the TCA cycle
- free amino acids can be catabolized for energy
- protein catabolism beings with hydrolysis of the peptide bonds that link amino acids together in the polypeptide chain – proteolysis
- the enzymes responsible = proteases
- all of the pathways for amino acid catabolism eventually lead to pyruvate, acetyl CoA, or a few key intermediates in the citric acid cycle
**amino acids can fuel the Krebs cycle