Question

During aerobic respiration maximum ATP is synthesized by

• A. ETS
• B. Kreb's cycle
• C. Glycolysis
• D. Fermentation

Answer 1

The correct option is A ETS

The complete oxidation of a glucose molecule leads to the net formation of 4 molecules of ATP by substrate-level phosphorylation (2 during glycolysis and 2 in the citric acid cycle), 2 molecules of NADH in the cytosol and 8 molecules of NADH plus 2 molecules of FADH2 (via succinate dehydrogenase) in the mitochondrial matrix. The glycolytic pathway also produces 2 molecules of NADH; therefore total 8+2=10 NADH are formed. During electron transport through the inner mitochondrial membrane, NADH pumps protons from complex I while FADH2 skips complex I and starts with complex II which in turn results in the synthesis of 3 and 2 molecules of ATP respectively. Therefore, 10 molecules of NADH power synthesis of 10*3=30 ATPs while 2 molecules of FADH2 power synthesis of 2*2= 4 ATPs. This makes total 4 molecules of ATP by substrate-level phosphorylation + 30 ATPs by electron transport via NADH + 4 ATPs by electron transport via FADH2= 38 ATPs. Fermentation is anaerobic respiration. Thus, the correct answer is option A.