Question

How many ATP is produced in the pay-off phase of glycolysis?
(a) 1
(b) 5
(c) 4
(a) 6

Answer 1

Hint: ATP is the universal energy carrier or currency of a cell and is released from substrates like glucose in the process of respiration. Glycolysis is a ten-step pathway grossly divided into two phases i.e preparatory phase and pay-off phase.

Complete answer:
Glycolysis is the first step common to both aerobic and anaerobic respiration. In this pathway, 6-C molecule glucose is oxidized to two 3-Carbon molecules of pyruvate whose scheme was given by Gustav Embden, Otto Meyerhof, and J Parnas, and thus, is also known as the EMP pathway.
This ten-step pathway is divided into the preparatory phase and the pay-off phase. In the preparatory phase, the energy is invested or consumed in the form of 2 ADP while in the payoff phase, energy is released or produced in the form of 4 ATP and 2 NADH.

Additional Information: Glycolysis occurs in the cytosol in the following manner:
-In the preparatory phase, glucose is phosphorylated by ATP to produce glucose-6-phosphate which isomerizes to fructose-6-phosphate.
-Another phosphorylation by ATP leads to the production of fructose-1,6-bisphosphate from fructose-6-phosphate.
-Fructose-1,6-bisphosphate is cleaved to produce two 3-C molecules. These are glyceraldehyde-3-phosphate and dihydroxyacetone phosphate.
-Dihydroxyacetone phosphate isomerizes to create Glyceraldehyde-3-phosphate. This ends the preparatory phase.
-The pay-off phase begins with the two molecules of Glyceraldehyde-3-phosphate converted to release 1,3-bisphosphoglycerate catalyzed by dehydrogenase coupled with the release of NADH.
-A high energy phosphate group is transferred from 1,3-bisphosphoglycerate to ADP. This leads to the generation of ATP and 3-phosphoglycerate.
-Isomerization of 3-phosphoglycerate to 2-phosphoglycerate is forwarded by the removal of a water molecule to release phosphoenolpyruvate.
-Glycolysis ends with an irreversible step of generation of ATP and the end product ‘pyruvate.’
So, the correct answer is ‘4.’

Note: -The product ‘pyruvate’ is further oxidized into acetyl-CoA. In eukaryotes, this reaction takes place in the matrix of mitochondria.
-Pyruvate is a charged molecule and thus requires a transport protein to enter mitochondria.
-Production of acetyl-CoA is the junction between glycolysis and the next step of aerobic respiration i.e Krebs cycle.