17.1 Pynuvate De ne respirati CITRIC ACID CYCLE OXIDATIVE PHOSPHORYLATION In ani

Question

17.1 Pynuvate De ne respirati CITRIC ACID CYCLE OXIDATIVE PHOSPHORYLATION In animal tissues, the rate of conversion of pyruvate to acety ratio of active, phosphorylated PDH complex to inactive, unphosphorylated PDH compiex. Determine whether there is an increase or decrease or unchanged reaction rate when a preparation of rabbit muscle mitochondria containing the PDH complex is treated with each of the following: (note - include an explanation; PDH stands for Pyruvate Dehydrogenase) (15 Points) 4. l-CoA is regulataed by the (a) pyruvate dehydrogenase kinase, ATP and NADH (b) pyruvate dehydrogenase phosphatase and Ca2* (c) sodium malonate (a competitive inhibitor of succinate dehydrogenase) oos not narticinate directly in the TCA cycle, the cycle operates o

Explanation / Answer

Regulation of pyruvate dehydrogenase:
i. ATP, NADH and Acetyl CoA inhibit PDH by allosteric/feedback mechanism
ii. Phosphorylation inactivates PDH. So, PDH kinase (PDK) represses PDH while PDH phosphatase (PDP) activates PDH.

a. In the presence of PDK, ATP, and NADH, PDH is inactivated.
b. In the presence of PDP and Ca+2, PDH is activated.
c. Sodium malonate inhibits one of the downstream reactions of the PDH complex. This will cause a reduction in ATP and NADH levels. So, this should promote PDH. At the same time, Acetyl CoA would be accumulated. This would inhibit PDH. However, the effect of the former is greater than the latter.

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