Biochem: 1. The TCA cycle uses high levels of NADH to regulate the activity of 3
ID: 72066 • Letter: B
Question
Biochem:
1. The TCA cycle uses high levels of NADH to regulate the activity of 3 of its enzymes (which ones?). A patient with a mutation in complex II of the electron transport chain lowers the electron accepting ability of the complex. Will this mutation greatly affect the body's ability to produce energy from glucose? Fatty acids? Explain your answer.
2. Glutamic acid can undergo a transamination with pyruvate to form a TCA intermediate. Suppose the indicated (*) carbon on glutamic acid is radiolabled prior to undergoing transamination.Where would the following carbon end up after it goes through the remainder of the TCA cycle to form citrate?
OH-C-*CH2-CH2-C-H (can't type out full glutamic acid but the indicated carbon is the first carbon in CH2).
3. How could the presence of the TCA cycle intermediate formed in the transamination reaction in problem 2 along with a mutated iso-citrate dehydrogenase 2 lead to cancer?
4. What problems are shared between people with pyruvate carboxylase and pyruvate dehydrogenase deficiencies? Can these diseases be treated? How? Explain.
5. The formation of GTP by Succinate Thiokinase is an example of substrate level phosphorylation that occurs without donating electrons to the electron transport chain. Is it possible to generate energy without the presence of oxygen using the succinate thiokinase reaction?
6. Malonate is structurally similar to Succinate. Malonate binds to Succinate Dehydrogenase in a seemingly irreversible manner thus inhibiting the function of the TCA cycle at this point. Assuming that one Acetyl-CoA molecule exists in solution and progresses through the TCA cycle and the ETC under incredibly high levels of malonate, how much energy is produced?
7. A stubborn child refuses to eat spinach, brussel sprouts, and red meat, all of which are a good source of lipoic acid. Which of the following enzymes would be affected by this child's diet? What other cofactors are required for these enzymes?
a. alpha keto gluterate dehydrogensase
b. Isocitrate dehydrogenase
c. pyruvate dehydrogenase
d. Malate dehydrogenase
8. Suppose you radioactively label the carbonyl carbon in Acetyl CoA and allow the molecule to go through the TCA cycle. Where will the carbon end up?
Explanation / Answer
1. Isocitrate dehydrogenase, alpha-ketoglutarate dehydrogenase, and malate dehydrogenase are the three enzymes regulated by high levels of NADH.
No this mutation will not affect the body’s ability to produce energy from Glucose or fatty acids, because NADH or NADPH are produced in large quantities than FADH2, which acts as an electron donor for complex II.
4. Pyruvate carboxylase deficiency is a genetic disorder that causes lactic acid and other toxic compounds to accumulate in the blood. Pyruvate dehydrogenase deficiency is characterized by the buildup of lactic acid in the body. In both cases lactic acid accumulation is observed. These two diseases are treatable.
Direct treatment that stimulates the pyruvate dehydrogenase complex (PDC), provides alternative fuels, and thus prevents this condition. Ketogenic diet, low carbohydrate and high fat intake are also used to minimize the lactic acid formation.
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