Question

1) Which of the following glycolysis intermediates can be generated from glycerol?

dihydroxyacetone phosphate

1,3-bisphosphoglycerate

glyceraldehyde-3-phosphate

3-phosphoglycerate

2) Which of the following is the oxidizing agent in the reaction that converts succinate to fumarate?

FAD, NADH, NAD+, succinate, Coenzyme A, or FADH2

3) Five NADH molecules in the mitochondria can be made into _____ number of ATP.

Answer 1

1) Glycerol is obtained from the hydrolysis of triacylglycerols in the presence of glycerol kinase enzyme that requires ATP. Now the glycerol is phosphorylated to produce glycerol-3-phosphate which can be channelised to produce dihydroxyacetone phosphate (DHAP), catalyzed by enzyme glycerol-3-phosphate dehydrogenase. This DHAP is an intermediate of glycolysis.

2) The conversion of succinate to fumerate requires the presence of oxidizing agent FAD. Succinate is dehydrogenated to fumerate, an unsaturated dicarboxylic acid, by succinate dehydrogenase. The hydrogen atoms are accepted by FAD. The FADH₂ then enters into ETC to generate ATPs. The enzyme is a flavoprotein. Here, FAD, acting as oxidizing agent, is reduced to FADH₂ and succinate is oxidized to fumerate.

3) The NADH generated during intermediary metabolism is oxidized through the electron transport system resulting in the production of ATPs. According to the estimated free energy of synthesis, it was presumed that around 3 protons are required per ATP synthesized. Hence, when one NADH transfers its electron to oxygen, 10 protons are pumped out. This would account for the synthesis of approximately 3 ATP. But the actual energy production is less, because there is always leakage of protons. This results in harnessing of energy required for the production of 2.5 ATP from NADH. So oxidation of one molecule of NADH yields 2.5 ATP. Now there are 5 NADH molecules in the mitochondria. Therefore, 5 molcules of NADH will yields $\left ( 2.5\times 5 \right )=12.5$ number of ATP molecules.