Question

Out of 38 molecules of ATP produced upon aerobic respiration of glucose, the break up in ATP production in glycolysis(P), pyruvate to acetyl-CoA formation(Q, and Krebs cycle(R) is as follows
a. P-2, Q=6, R=30
b. P=8, Q=6, R=24
c. P=8, Q=10, R=20
d. P-2, Q=12, R=24

Answer 1

Hint: In aerobic respiration initially glucose converts pyruvic acid which takes place in the cytoplasm and the process is called glycolysis, later this pyruvic acid converted to acetyl CoA, and enters the Krebs cycle and ATP is formed, later they enter the electron transport chain.

Complete answer:
( P ) The first one is glycolysis, it takes place in the cytoplasm as all the enzymes required for this process present in the cytoplasm of the cells.
- In the glycolysis cycle, In the first 2 steps glucose undergoes the phosphorylation.
- Later it forms into fructose 1-6 bisphosphate. During this conversion into 1-3 bisphosphoglycerate in the presence of enzyme 3 glycerophosphate dehydrogenase , it forms two NADH.
- 1-3 bisphosphoglycerate undergo substrate level phosphorylation to produce 2 ATP.
- Second substrate level phosphorylation occurs by the enzyme pyruvate kinase to produce 2 ATP.
- One should remember that one NADH is equal to 3 ATP.
- In the beginning of glycolysis at the time of phosphorylation steps 2 ATP are consumed.
- So Total ATP in glycolysis is 8

Steps	ATP produced
3 glycerol phosphate dehydrogenase	2 NADH = 6 ATP
Substrate level phosphorylation 1	2 ATP
Substrate level phosphorylation 2	2 ATP
Total	10 ATP
During first two steps of Glycolysis 2 ATP are consumed so that 10 – 2 = 8 ATP in ( P )

( Q ) After conversion of glucose molecules to pyruvic acid they in turn convert to Acetyl CoA.
In this process 2 NADH are produced. As it was said previously 1 NADH = 3 ATP, so here two pyruvic acid converts as we already know that one glucose splits to two pyruvic acids so a total of 6 ATP is formed.

( R ) Once Acetyl coA formed it entered into the krebs cycle .
In krebs cycle ATP are produced in the following step enzymes. So in the stage of ( R ) it is 24 ATP.

Enzymes of Krebs cycle	No of energy molecules	No of ATP
Isocitrate dehydrogenase	2 NADH	6 ATP
Alpha ketoglutarate dehydrogenase	2 NADH	6 ATP
Succinate Thiokinase	Substrate level phosphorylation	2 ATP
Succinate dehydrogenase	2 FADH	4 ATP
Malate dehydrogenase	2 NADH	6 ATP
Total	-	24 ATP

Hence, The correct answer is option (B).

Note: In some steps of whole process instead of direct ATP production, there is a formation of NADH and FADH molecules, one should always remember that one NADH is equal to 3 ATP and one FADH is equal to 2 ATP, so in the whole process of all cycles, one glucose molecule gives 38 ATP.