TCA Cycle Flashcards
What two oxidative decarboxylation reactions are carried out in the TCA cycle?
Oxidative decarboxylation is an irreversible oxidation process. The carboxyl group is removed as CO2 and replaced with a thioester derivative of CoA.
Isocitrate dehydrogenase catalyzes oxidative decarboxylation of isocitrate to form alpha-ketogluterate in the TCA cycle.
alpha-ketoglutarate dehydrogenase…
What are some similarities between pyruvate dehydrogenase and alpha-ketoglutarate dehydrogenase?
Protein structure (3 enzymes in one complex)
Cofactor requirements (NAD+, lipoic acid, TPP, FAD, CoA)
The reaction mechanism (oxidative decarboxylation)
How does the structure of CoA help to facilitate the acceptance and “deliver” of acetyl groups on and from CoA?
The reactive thiol group on CoA covalently links acyl groups forming a thioester which have a high group transfer potential.
Use an example from the TCA cycle to describe the term “flux.”
The rate of flow can be limited by the availability of NAD+. If NAD+ is depleted by conversion to NADH, it will slow the three NAD-dependent oxidation steps.
True or false: Oxaloacetate is an intermediate of the citric acid cycle.
True
T or F: Citrate is an intermediate of the citric acid cycle.
T
T or F: alpha-ketogluterate is in intermediate of the citric acid cycle.
T
T or F: Succinyl-CoA is in intermediate of the citric acid cyle.
T
T or F: Pyruvate is in intermediate of the citric acid cycle.
F
What would be the consequence of replacing the sulfhydryl group of CoA with an OH group?
The sulfhydryl group of CoA covalently links to acyl groups and the thioester has a high standard free energy of hydrolysis resulting in a high acyl group transfer potential. If the -SH was replaced with an alcohol group, resulting in an ester instead when acyl group covalently bonds, the reactivity would be lowered with less transfer potential.
What are the control steps for the TCA cycle?
Citrate synthase
Isocitrate dehydrogenase
alpha-ketoglutarate dehydrogenase complex
T or F: The TCA cycle is an anabolic pathway
F. The TCA cycle is an amphibolic pathway
In what cellular location does the TCA cycle take place?
Mitochondria
Compare the overall reaction for the TCA cycle to the overall reaction for glycolysis.
Glycolysis is a linear metabolic pathway where the catabolic breakdown of one molecule of glucose to yield two molecules of pyruvate allows the release of free energy from glucose and conserved in the form of ATP and NADH.
The TCA cycle is a cyclic pathway where multiple reactions yield a product (oxaloacetate) that reacts with the starting product (acetyl-CoA), thus creating a cyclic pathway. The energy released during these reactions is conserved in the form of the reduced coenzymes NADH and FADH2.
How is pyruvate dehydrogenase regulated by covalent modification?
Phosphorylated PDH renders the enzyme inactive.
PDH kinase is the enzyme that phosphorylates PDH.
PDH kinase activity is stimulated by increased concentrations of mitochondrial ATP, NADH, and acetyl-CoA.
If concentrations of pyruvate are high, they will bind to PDH kinase and prevent the phosphorylation oof PDH and therefore prevent the inactivation of PDH phosphatase which removes the phosphate group from the inactive phosphorylated PDH.
