biochem citric acid cycle
One-turn of the citric acid cycle yields __________.
1 ATP (GTP), 3 NADH, 1 FADH2, and 2 CO2
How many carbon dioxide molecules will be released for the complete oxidation of the following molecules? (1) glucose (2) pyruvate (3) acetyl-CoA
1. 6 2. 3 3. 2
How many carbon atoms do each of the following molecules contain? (1) citrate (2) alpha-ketoglutarate (3) OAA (4) Acetyl group on CoA
1. 6 2. 5 3. 4 4. 2
How many turns of the citric acid cycle are required to oxidize the carbons from acetyl-CoA?
2
Which of the following allosteric inhibitors for the pyruvate dehydrogenase complex (PDC) is a type of feedback inhibition?
ATP,is a feedback inhibitor of the PDC, as ATP is a final product of oxidative phosphorylation. Feedback inhibition occurs when the final product, or intermediate near the end of a pathway, inhibits the beginning of the pathway.
Which of the following is NOT a product of the citric acid cycle? Acetyl-CoA, CO2, NADH, ATP
Acetyl-CoA
Isocitrate dehydrogenase is down-regulated by which method?
Allosteric inhibition,High [NADH] inhibits isocitrate dehydrogenase, which is an example of product inhibition since this is the product of the isocitrate dehydrogenase-catalyzed reaction. Isocitrate dehydrogenase is not a zymogen nor is it under phosphorylation control. This enzyme is also feedback inhibited (not activated) by ATP, the product of oxidative phosphorylation. Also [ADP] allosterically up-regulates this enzyme.
Which enzyme in the citric acid cycle is responsible for catalyzing the rate-limiting step?
Alpha-ketoglutarate dehydrogenase
Fully oxidized carbon leaves the citric acid cycle as this chemical __________.
CO2
Carbon atoms enter the citric acid cycle in the reaction involving which enzyme?
Citrate synthase
Which of the following statements is FALSE concerning the pyruvate dehydrogenase complexes (PDC or PDH)? FADH2 is a product, it uses coenzyme A as a substrate, it requires TPP as a coenzyme, lipoic acid is covalently bound to E2, pyruvate is oxidized 2 acetyl-CoA, therefore linking glycolysis & the citric acid cycle
FADH2 is a product,FAD is reduced to regenerate lipoamide. In return, FADH2 is re-oxidized (regenerated) by reducing NAD+ to NADH. Since this coenzyme is regenerated and does not dissociate from the PDC, it is not a product.
Consider the reaction that generates an NTP in the citric acid cycle. Which of the following is a driving force for this reaction?
Hydrolysis of the thioester bond releases energy that is coupled to the formation of the phosphoanhydride bond in ATP (GTP).
Which of the following coenzymes is NOT tightly/covalently bound to the pyruvate dehydrogenase complex (PDC)?
NAD+
Citrate synthase is inhibited by high concentrations of __________.
NADH, as this is a signal that oxygen concentration is low and/or ATP no longer needs to be made.
Does the citric acid cycle directly require oxygen (O2)?
No, oxygen (O2) is not a substrate for any of the enzyme-catalyzed reactions.Molecular oxygen is indirectly necessary for the citric acid cycle via the electron transport chain. The electron transport chain oxidizes NADH to NAD+, which is necessary for the citric acid cycle to continue running. Oxygen is the final electron acceptor in the electron transport chain, and is therefore needed to oxidize NADH.
Which enzyme-catalyzed reaction in the citric acid cycle generates NAD+?
None of the citric acid cycle reactions generate NAD+.
Which enzyme-catalyzed reaction in the citric acid cycle generates H2O? rxn catalyzed by citrate synthase, fumarase or aconitase
None of the enzyme-catalyzed reactions in citric acid cycle generates water. However, three reactions use water and these are catalyzed by citrate synthase, fumarase, and aconitase.
The first reaction of the citric acid cycle, where acetyl-CoA and __________ combine to form citrate, is catalyzed by __________.
OAA; citrate synthase, to produce a six-carbon intermediate called citrate.
If a person were deficient in vitamin B5, which enzyme-catalyzed reaction in the citric acid cycle would be directly affected?
The reaction catalyzed by alpha-ketoglutarate dehydrogenase
Which enzyme-catalyzed reaction in the citric acid cycle generates CO2?
The reaction catalyzed by isocitrate dehydrogenase
If a person were deficient in vitamin B3, what enzyme-catalyzed reaction in the citric acid cycle would be directly affected?
The reaction catalyzed by malate dehydrogenase
Which of the following enzyme-catalyzed reactions in the citric acid cycle generates NADH?
The reaction catalyzed by malate dehydrogenase
If a person were deficient in vitamin B2, what enzyme-catalyzed reaction in the citric acid cycle would be directly affected?
The reaction catalyzed by succinate dehydrogenase
Which enzyme-catalyzed reaction in the citric acid cycle generates FADH2?
The reaction catalyzed by succinate dehydrogenase
Which enzyme-catalyzed reaction in the citric acid cycle generates an NTP (where N = any nitrogenous base)?
The reaction catalyzed by succinyl-CoA synthetase
Why are citrate synthase, isocitrate dehydrogenase, and alpha-ketoglutarate dehydrogenase good candidates for regulation of the citric acid cycle?
These enzymes catalyze the irreversible reactions in the citric acid cycle.
A-ketoglutarate dehydrogenase is regulated by which of the following?
allosteric inhibition, allosteric activation, general base, high, product inhibition
Of the choices below, which is the LEAST oxidized molecule? citrate, oxaloacetate, succinate, malate, alpha-ketoglutarate
citrate
Where in a eukaryotic cell does the citric acid cycle occur?
mitochondrial matrix
Which of the following enzymes does NOT catalyze an irreversible reaction in the citric acid cycle? succinate dehydrogenase, citrate synthase, isocitrate dehydrogenase, alpha-ketoglutarate dehydrogenase
succinate dehydrogenase
During the reaction catalyzed by the pyruvate dehydrogenase complex (PDC), the acetyl group taken from pyruvate is covalently linked to what type of atom in lipoamide?
sulfur
The acetyl group in acetyl coenzyme A is covalently linked to what type of atom?
sulfur
