Question

Pyruvate dehydrogenase is the entry point for the glycolytic product pyruvate into oxidative metabolism (the citric acid cycle and oxidative phosphorylation). Because it occupies such an important checkpoint in metabolism, it is tightly regulated. Determine whether the given conditions promote entry into oxidative metabolism or limit entry into oxidative metabolism. These abbreviations may be used: PDH is pyruvate dehydrogenase; PDK is pyruvate dehydrogenase kinase; PDP is pyruvate dehydrogenase phosphatase.(1) Oxidative metabolism increase(2) Oxidative metabolism is limited(A) Low O2 level, PDK active(B) High O2 level, active PDH(C) High O2 level, PDK inhibitor present(D) High O2level, inactive PDH(E) High O2 level, active PDK

Answer 1

(1) Oxidative metabolism increase. As oxidative metabolism increases, there is less need for glycolytic products to enter oxidative phosphorylation hence this limits entry into oxidative metabolism

(2) Oxidative metabolism is limited. As oxidative metabolism is decreased, there is increased need for glycolytic products to enter the oxidative phosphorylation to produce more ATP hence this promotes entry into oxidative metabolism.

(A) Low O2 level, PDK active. As PDK is active, pyruvate dehydrogenase is phosphorylated and inactivated, thus limiting entry into oxidative metabolism.

(B) High O2 level, active PDH. With high o2, there is increased final electron acceptors in oxidative phosphorylation hence there is increased rate of oxidative metabolism and thus entry is promoted, as acetyl CoA is used up at a faster rate.

C) High O2 level, PDK inhibitor present. PDK inhibitor activates PDH hence entry is promoted.

(D) High O2level, inactive PDH. PDH inactive hence entry is limited.

(E) High O2 level, active PDK. PDH inactivated by PDK hence entry is limited. although if you consider anaplerotic reactions into TCA cycle, the entry through other means may not be limited.

Answer 2

Step-by-step explanation:

1. Low O2 levels, PDK active- when PDK is active PDH is inactive, oxidative metabolism is limited

High O2 levels, active PDH- oxidative metabolism is increased

High O2 levels, PDK inhibitor present- PDH is active, oxidative metabolism is increased

High O2 levels, inactive PDH- oxidative metabolism is limited

High O2 levels, PDPK active- , oxidative metabolism is increased

PDH is regulated via phosphorylation by PDK: when PDK phosphorylates PDH, it becomes inactive. The opposite of that PDK activated PDH by dephosphorilation of PDH.