Question

Pyruvate must move from the cytosol into the mitochondria, where it is oxidized to form CO₂ and acetyl CoA by the pyruvate dehydrogenase complex. How many different enzymes and what is the total number of polypeptides, respectively, required to perform this oxidation process in the mitochondrion?

Answer 1

The PDHC, responsible for the oxidation of pyruvate to acetyl CoA, consists of three core enzymes: pyruvate dehydrogenase, dihydrolipoyl transacetylase, and dihydrolipoyl dehydrogenase. There are a total of 60 polypeptides in the human PDHC. NADH is produced in the process, which then assists in ATP production during the electron transport chain.

Step-by-step explanation:

The oxidation of pyruvate to acetyl CoA in the mitochondrion involves a multi-enzyme complex called the pyruvate dehydrogenase complex (PDHC). This complex is made up of three core enzymes: pyruvate dehydrogenase (E1), dihydrolipoyl transacetylase (E2), and dihydrolipoyl dehydrogenase (E3). Together, these enzymes perform the oxidative decarboxylation of pyruvate, ultimately transforming it into acetyl CoA while releasing carbon dioxide (CO2) and transferring electrons to NAD+ to form NADH.

In terms of the number of polypeptides, the entire PDHC consists of multiple copies of these three enzymes. Specifically, the human PDHC has 30 copies of E2, and multiple copies of E1 and E3, summing up to a total of 60 polypeptides. This large complex ensures efficient catalysis of the reaction where each pyruvate molecule loses a CO2 molecule and yields an acetyl CoA. This acetyl CoA then enters the Krebs cycle, and the NADH produced moves on to the electron transport chain to facilitate ATP production.