Question

BIOCHEMISTRY

10. Draw structures and write the overall reaction in the citric acid cycle for each step described below:

1. Reaction catalyzed by an enzyme similar to PDH

2. The step in which the reaction product inhibits PFK

3. The step that involves isomerization and an enzyme with Fe-S clusters

4. A reaction that produces substrate level phosphorylation

5. A decarboxylation step coupled to the production of a high energy intermediate

6. A reaction that involves the production of a reduced flavin coenzyme

7. A reaction that is not thermodynamically favored under standard conditions

8. A reaction that involves an enzyme similar to PDH

Answer 1

Krebs cycle is also called citric acid cycle or tricarboxylic acid cycle. It includes step wise cyclic process, in which pyruvate (from glycolysis), is oxidised to ultimately form water and carbon dioxide. The products formed during the cycle, include CO2, electron carriers- NADH and FADH2, which are used to generate ATP.

The phases of Krebs cycle include:

Phase I of Krebs cycle:

· Entry of Acetyl Co-A- combines with 4- carbon Oxaloacetate.

· 6 carbon Citrate is produced

Phase II of Krebs cycle:

· Citate is converted to iso-citrate.

· Isocitrate is oxidized to 5- carbon α-Ketogluterate.

· Reduces NAD+ to NADH + H (step 3)

· α-Ketogluterate is converted to Succinyl CoA, also NADH + H is produced (step 4).

· Succinate converted to fumerate, also generates FADH2 (step 6).

Phase III of Krebs cycle:

· Malate is oxidized to Oxaloacetate to reinitiate the cycle. NAD is reduced to NADH+H (step 8).

Reaction catalyzed by an enzyme similar to PDH

The step in which the reaction product inhibits PFK

The step that involves isomerization and an enzyme with Fe-S clusters

A reaction that produces substrate level phosphorylation

A decarboxylation step coupled to the production of a high energy intermediate

A reaction that involves the production of a reduced flavin coenzyme

A reaction that is not thermodynamically favored under standard conditions

A reaction that involves an enzyme similar to PDH