Cellular respiration can be studied in isolated mitochondria by measuring oxygen
ID: 211894 • Letter: C
Question
Cellular respiration can be studied in isolated mitochondria by measuring oxygen consumption under different conditions. Malonate is a structural analog of succinate and a competitive inhibitor of succinate dehydrogenase. If malonate is added to actively respiring mitochondria, respiration will stop. [20 pts 1. What intermediate will accumulate with the addition of sodium malonate? (5 pts) 2. How many cofactors, if any, will you produce if two (2) pyruvate molecules head for the TCA cycle, in the presence of malonate? EXPLAIN your answer. (10 pts) 3. Aside from the removal of malonate, how can this inhibition of respiration be overcome? (5 pts)Explanation / Answer
Succinate dehydrogenase catalyzes the following reaction.
Succinate + FAD ----> Fumarate + FADH2
1. If succinate dehydrogenase is inhibited, its substrate i.e. succinate will accumulate.
2. From glycolysis, 1 glucose produces 1 NADH and 2 pyruvates.
One pyruvate produces 1 NADH during oxidative decarboxylation to produce Acetyl CoA.
One Acetyl CoA produces 2 NADH and 1 GTP up to the step of succinate dehydrogenase.
So, two pyruvates will produce 3 X 2 = 6 NADH molecules (Including oxidative decarboxylation step)
3. Malonate is a competitive inhibitor of succinate dehydrogenase. Since it is a competitive inhibitor, the enzyme inhibition can be relieved by increasing its substrate concentration i.e. increasing the concentration of Succinate.