Chapter 17: The Citric Acid Cycle Flashcards
Why is FAD used instead of NAD+ is used by succinate dehydrogenase?
FAD is used instead of NAD+ because there is not enough reduction potential for FAD to overcome to be able to use NAD+. It produces about 1.5 ATP in comparison to 2.5 ATP from NADH.
What are the regulators for the citric acid cycle?
The regulators are pyruvate dehydrogenase, isocitrate dehydrogenase and alpha-ketoglutarate.
-ATP inhibits pyruvate dehydrogenase and isocitrate dehydrogenase
-NADH inhibits pyruvate dehydrogenase and alpha-ketoglutarate dehydrogenase
-Fatty acids also inhibit pyruvate dehydrogenase.
What compounds can be made from citrate?
Fatty Acids and steroids
What compounds can be made from alpha ketoglutarate?
Glutamate, Other amino acids and purines
What compounds can be made from succinyl CoA?
Porphyrins, heme and chlorophyll
What compounds can be formed from oxaloacetate?
Glucose, aspartate, other amino acids, purines and pyrimidines
What is E1 of the pyruvate dehydrogenase?
Draw it. TPP is the cofactor that takes pyruvate and removes a CO2 group.
What is E2 of the pyruvate dehydrogenase?
Draw it. Lipoamide is the cofactor that has a disulfide bond. Acetyl CoA is formed here and the reduced form of lipoamide.
What is E3 of the pyruvate dehydrogenase?
Draw it. This portion contains FAD to bring the oxidized molecule of lipoamide to the reduced form and FADH2. FADH2 then gives the electron to NADH to get FAD back for the complex.
Why does a B1 deficiency (thiamine) lead to neurological symptoms as opposed to liver or muscular symptoms?
A deficiency in thiamine (B1) would cause pyruvate dehydrogenase to shut down. Skeletal muscle can function without pyruvate dehydrogenase. Fatty acids can give acetyl CoA and b-oxidation of fatty acids for the heart muscle that needs to run the CAC all the time. The brain and nervous tissue rely on glucose. The problem occurs when pyruvate dehydrogenase is shut down and fatty acids cannot pass the blood brain barrier. That is why this deficiency leads to neurological symptoms and not other issues.
Mneumonic:
Citrate
Is
Krebs
Starting
Substrate
For
Making
Oxaloacetate
Citrate
Isocitrate
alpha-ketoglutarate
Succinyl CoA
Succinate
Fumarate
Malate
Oxaloacetate
What are the enzymes in order for the citric acid cycle?
Aconitase
Isocitrate dehydrogenase
Alpha-ketoglutarate dehydrogenase
Succinyl CoA synthetase
Succinate dehydrogenase
Fumarase
Malate dehydrogenase
Explain the importance of pyruvate carboxylase to the citric acid cycle.
Pyruvate carboxylase is the first enzyme in gluconeogenesis. This enzyme catalyzes the step of pyruvate to oxaloacetate. Oxaloacetate is very important to the citric acid cycle. Components of the citric acid cycle can be used to produce amino acids and other things so when those components leave the cycle the amount of oxaloacetate decreases. If there is not enough oxaloacetate the cycle will stop, so the production of oxaloacetate in gluconeogenesis is vital to keep the citric cycle replenished with this intermediate to continue the cycle.
