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Example Questions
Example Question #1 : Citric Acid Cycle Regulation
In which of the following cases would the citric acid cycle be downregulated?
High levels of ATP
Lower levels of NADH
Increased amounts of
High levels of ADP
High levels of ATP
The purpose of the citric acid cycle is to produce energy (both directly via GTP, and indirectly via NADH and . As such, energy can be though of to be on the products side of the sum of the reactions of the Krebs cycle. From Le Chatelier's principle, we know that if we want to inhibit a forward reaction, we can increase the concentration of the products. This will inhibit the forward reaction, and push the equilibrium to the left. Thus, in a high energy state, the ratio of ATP:ADP, like that of NADH: is high since both ATP and NADH are products of metabolism.
Example Question #1 : Citric Acid Cycle Regulation
Why can't acetyl-CoA produced from beta-oxidation enter into the Krebs Cycle without carbohydrates present?
Acetyl-CoA must first be activated by a carbohydrate before entering into the Krebs cycle
Acetyl-CoA combines with oxaloacetate to enter into the Krebs cycle which is a carbohydrate
Acetyl-CoA can enter into the Krebs cycle without carbohydrates present
Downstream of the Krebs cycle, the electron transport chain can not function without carbohydrates present, which in turn causes the Krebs cycle to stop functioning
None of these
Acetyl-CoA combines with oxaloacetate to enter into the Krebs cycle which is a carbohydrate
The entry point for acetyl CoA in the Krebs cycle is oxaloacetate. Acetyl-CoA and oxaloacetate combine to form citrate, which then continues through the cycle. Oxaloacetate is a carbohydrate, and so without carbs the acetyl-CoA can not enter into the Krebs cycle.
Example Question #2 : Citric Acid Cycle Regulation
Which of the following is not a regulated step of the citric acid cycle?
None of these
Citrate synthase
Alpha-ketoglutarate dehydrogenase
Isocitrate dehydrogenase
Succinate dehydrogenase
Succinate dehydrogenase
The regulated steps of the citric acid cycle are citrate synthase, isocitrate dehydrogenase, and alpha-ketoglutarate dehydrogenase. These steps are inhibited and stimulated by various products and reactants within the citric acid cycle. Succinate dehydrogenase is not regulated by products or reactants, and is therefore not rate limiting.
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