Question

When a glucose molecule is metabolized completely into CO2 and H2O, how many substrate level phosphorylation steps are there and how many ATP’s in total are produced in these steps?

a.) 3 steps, 3 ATP/GTP

b.) 4 steps, 4 ATP/GTP

c.) 3 steps, 6 ATP/GTP

d.) 2 steps, 4 ATP/GTP

e.) 2 steps, 2 ATP/GTP

Answer 1

Answer: d.) 2 steps, 4 ATP/GTP

Explanation:

The formation of ATP, by the transfer of phosphate from an organic compound to ADP, is called substrate level phosphorylation. In glycolysis, at two steps substrate level, phosphorylations occur. The first substrate, level phosphorylation occurs by dephosphorylating 1,3-bisphosphoglycerate by phosphoglycerate kinase, producing 3-phosphoglycerate and ATP. The second substrate level, phosphorylation occurs by dephosphorylating phosphoenolpyruvate, catalyzed by pyruvate kinase, producing pyruvate and ATP.

Glycolysis starts with one molecule of glucose and ends with two pyruvate (pyruvic acid) molecules, a total of four ATP molecules, and two molecules of NADH.

So the answer is “d.) 2 steps, 4 ATP/GTP”