AP BIOLOGY

Detailed explanation-1: -Substrate level phosphorylation is the synthesis of ATP from ADP during an energy-yielding reaction of glycolysis or Krebs cycle. The high-energy phosphate group pf phosphoenolpyruvate is transferred to ADP, forming pyruvic acid and ATP.

Detailed explanation-2: -During glycolysis, there are two steps at which substrate level phosphorylation occur when glyceraldehyde-3-phosphate is converted into pyruvic acid. Therefore, in the glycolysis of one glucose molecule, number of substrate level phosphorylation occurs 4 times.

Detailed explanation-3: -Pyruvate kinase not only catalyses substrate-level phosphorylation yielding ATP (Clinical box 3.3), but it is also another regulatory enzyme of glycolysis, although its action is in direct contrast to the ATP-consuming reactions catalysed by the other regulatory enzymes, HK and PFK-1.

Detailed explanation-4: -In cellular respiration and fermentation, substrate-level phosphorylation occurs in both glycolysis and the citric acid cycle.