Question

A substrate-level phosphorylation occurs in the citric acid cycle when _____.

a. atp is hydrolyzed to adp.
b. nad+ is phosphorylated to nadh.
c. gdp is phosphorylated to produce gtp
d. pyruvate is oxidized

Answer 1

Substrate-level phosphorylation in the citric acid cycle occurs when GDP is phosphorylated to produce GTP, a reaction catalyzed by succinyl-CoA synthetase.

Step-by-step explanation:

A substrate-level phosphorylation occurs in the citric acid cycle when GDP is phosphorylated to produce GTP. This process happens specifically in the reaction catalyzed by succinyl-CoA synthetase, where the energy released by the hydrolysis of the high-energy thioester bond of succinyl-CoA is used to form guanosine triphosphate (GTP) from guanosine diphosphate (GDP) and inorganic phosphate. GTP can then readily transfer its terminal phosphate group to adenosine diphosphate (ADP) to generate ATP.

Unlike oxidative phosphorylation, which produces ATP through the electron transport chain and chemiosmosis, substrate-level phosphorylation occurs directly during catabolic pathways. A phosphate group is transferred from an intermediate to an ADP molecule, thereby generating ATP. In the context of the citric acid cycle, the correct answer given the options provided is c. GDP is phosphorylated to produce GTP.

Answer 2

C. GDP is phosphorylated to produce GTP
Substrate level phosphorylation occurred in kreb cycle inform of metabolic reaction that involve the transfer of phosphoryl group to GDP or ADP from another phosphorylated compound which result into formation of GTP or ATP. This process commonly occurs in the cytoplasm of cells during glycolysis and also in the mitochondria during krebs cycle.