Question

16. Why does FADH2 provide energy for 1.5 ATP molecules in the ETC, whereas NADH provides energy for 2.5 ATP molecules? ( Show calculations. )






17. How does each of the following regulate the CAC:

       a/ high levels of NADH
     
      
       b/ high levels of ATP
     
      
       c/ high levels of ADP

      
       d/ low levels of NADH




18. Where is ATP synthase for oxidative phosphorylation located in the cell?




19. Why do H+ leave the intermembrane space and return to the matrix of the mitochondrion?





20. Why do the enzyme complexes that pump H+ extend across the mitochondrial membrane from the matrix to the intermembrane space?

Answer 1

Ans :-16) To pass the electrons from NADH to last oxygen acceptor, total 10 protons are transported from matrix to inner mitochondrial membrane. ( 4 electrons via complex 1, 4 electrons via complex 3 and 2 electrons via complex 4.To make 1 ATP, 4 electrons move from inner mitochondrial membrane to matrix via ATPase.

Thus for NADH :- 10/4 =2.5ATP are produced actually.

Similarly for 1 FADH2, six protons are moved so 6/4 = 1.5ATP is produced.

Ans :-17) CAC means citric acid cycle. This is regulated as :-

(a) High level of NADH :- NADH is byproduct of reaction and act as inhibitor . If the level of NADH is high then it inhibits iso citrate dehydrogenase by directly displacing NAD+. Thus it will stop the cycle. Alpha ketoglutarate dehydrogenase is also inhibited by NADH.

B) High level of ATP :- ATP is allosteric inhibitor of enzyme citrate synthase. If level of ATP is high then synthesis of citrate will be very low. Rate of cycle is reduced when ATP is high.

C) high level of ADP :- When ADP levels are higher than ATP, the cell needs energy and hence NADH is oxidised rapidly and the citric acid cycle is accelerated.

D) low level of NADH :- since NADH inhibits many enzymes in citric acid cycle. So if level of NADH is low then citric acid cycle will get accelerated.

Ans :-18) ATP synthase is located in mitochondria of eukaryotic cell (inner mitochondrial membrane).Its F1 part projects in mitochondrial matrix.

Ans :-19)