Question

At how many steps there occurs substrate level phosphorylation in glycolysis?
a. One
b. Two
c. Three
d. Four

Answer 1

Hint: Substrate-level phosphorylation is a chemical reaction that results in the creation of ATP or GTP by conversion of a higher energy substrate (whether phosphate group attached or not) into a minor energy product and a utilizing some of the exuded chemical energy, the Gibbs free energy, to transport a phosphoryl group to ADP or GDP from a new phosphorylated compound.

Complete answer:
Substrate level phosphorylation takes place during glycolysis. In this route phosphorylation (that is addition of phosphate group) to Glucose (substrate). This shift occurs at two steps, the 1st step or the preparatory phase, by enzyme Hexokinase and after that where Fructose-1-phosphate is changed to Fructose-1, 6-bisphosphate.

In the next phase also called the payoff phase the two ATP molecules used are synthesized or given back to the system. This also happens in two stages -
- The transformation of 1, 6 Bisphosphoglycerate to 6-phosphoglycerate releases 1 ATP molecule and
- In the very last stage where phosphoenolpyruvate is switched to pyruvate.

The creation of ATP, by the transport of phosphate from an organic compound to ADP, is known as substrate-level phosphorylation.

Hence, the correct answer is option (B).

Note: The net energy liberated in glycolysis is an effect of two molecules of glyceraldehyde-3- phosphate ingoing the second half of glycolysis where they are transformed into pyruvic acid. Substrate-level phosphorylation, where a substrate of glycolysis contributes a phosphate to ADP, arises in two steps of the second half of glycolysis to produce ATP. The accessibility of NAD+ is a restraining factor for the steps of glycolysis; when it is out of stock; the second half of glycolysis slows or shuts down.