Question

How many ATPs are synthesized per sucrose molecule (gross synthesis) in aerobic respiration through substrate-level phosphorylation?
(a) 10
(b) 12
(c) 30
(d) 76

Answer 1

Hint: Each glucose molecule gives a net gain of 36ATP in that 5ATP molecules are from substrate-level phosphorylation in aerobic respiration. Two molecules of glucose form a sucrose molecule.

Complete step by step answer:
In the process of glycolysis, two substrate-level phosphorylation one is during the conversion of 1,3 bisphosphoglyceric acid to 3-phosphoglyceric acid where 2ATPs is released and second, substrate-level phosphorylation occurs during the conversion of phosphoenolpyruvate to pyruvic acid which gives 2ATPs. In the Kreb cycle, one substrate-level phosphorylation occurs during the conversion of succinyl CoA to succinic acid which releases 1 ATP molecule. For a molecule of glucose, 5ATP molecules are produced in substrate-level phosphorylation and for one sucrose molecule 10ATP molecules are produced

Additional information:
- One molecule of glucose in glycolysis gets converted into 2 pyruvate molecules releasing 2ATP molecules and 2NADH molecule
- From the link pathway between glycolysis and Kreb cycle, pyruvate gets converted into acetyl CoA by releasing 1NADPH molecule for one pyruvate.
- In the Kreb cycle, 1ATP, 3NADH, and 1 ${ FADH }_{ 2 } $ are released for one molecule of pyruvate.
- In glycolysis, 2molecules of pyruvate are produced.1 NADPH molecule gives 3 ATP and
1 ${ FADH }_{ 2 }$ molecule gives 2ATP molecules.
- So the net gain of ATP for one glucose molecule is 38 ATP and two molecules of glucose give one sucrose molecule. So one sucrose molecule gives 76ATP molecules
- three substrate-level phosphorylation occurs in aerobic respiration i.e, during the conversion of 1,3 bisphosphoglyceric acid to 3-phosphoglyceric acid, during the conversion of phosphoenolpyruvate to pyruvic acid, during the conversion of succinyl CoA to succinic acid
$1,3\quad bisphosphoglyceric\quad acid\xrightarrow [ ADP->ATP ]{ phosphoglycerokinase } { 3-phosphoglyceric\quad acid }\\ { 2-phosphoenolpyruvate\xrightarrow [ ADP->ATP ]{ pyruvic\quad kinase } { pyruvic kinase } }\\ { Succinyl\quad CoA }+ADP+PI\xrightarrow { succinic\quad kinase } succinic\quad acid\quad +ATP+CoA$
So, the correct answer is ‘10’.

Note:
- Each NADPH molecule gives 3 ATP Molecules and each ${ FADH }_{ 2 }$ molecule gives 2ATP molecules.
- Two glucose molecules combine together and form a sucrose molecule.