ATP is synthesized by substrate-level phosphorylation during which of the following?

A. glycolysis only conversion of pyruvate to lactate

B. only Krebs cycle

C. only glycolysis and the Krebs cycle

D. only glycolysis, the Krebs cycle, and during the conversion of pyruvate to lactate

Answer: Option C.

Only glycolysis and the kreb cycle.

Explanation:

Substrate level phosphorylation is the process by which ATP is synthesized due to addition of phosphate group to ADP, catalysed by enzyme ATP synthase. This take place only in glycolysis and mitochondrial matrix during kreb cycle.

Glycolysis takes place in cytoplasm of the cell.

Two ATP molecules from breakdown of glucose, which is called pyruvate in the cytoplasm which produced four ATP during substrate phosphorylation. Two NADH molecules are produced which is used to produced 3 to 5 ATP molecules in the mitochondrial through electron transport chain. The kreb cycle produced ATP, NADH and FADH2 through the oxidation of pyruvate produced from glycolysis.

C. only glycolysis and the Krebs cycle

Explanation:

Conversion of 1,3-bisphosphoglycerate into 3-phosphoglycerate and conversion of phosphoenolpyruvate into pyruvate during glycolysis obtains a total of 4 ATP molecules per glucose (2 from each reaction). Here, ATP formation occurs by the transfer of the phosphoryl group from a substrate such as 1,3-bisphosphoglycerate. Therefore, it is called a substrate-level phosphorylation.

Similarly, oxidative decarboxylation of alpha-ketoglutarate into succinyl CoA and conversion of succinyl CoA into succinate forms 2 ATP molecules per glucose during Kreb's cycle. Here, the energy for ATP synthesis is provided by oxidative decarboxylation of a substrate. Therefore, it is also substrate-level phosphorylation.