Citric Acid Cycle

Question 1

What is the citric acid cycle?

Answer 1

• completely oxidizes the 2-C acetyl group to 2-CO2 with dehydrogenase
• this results in 3 NADH, 1 FADH2 (both are reduced electron carriers) and 1 GTP = ATP
• no 02 is needed, but the amount of NADH generated can only be oxidized with O2

Question 2

Step 1

Answer 2

• acetyl-CoA, a 2-C molecule, hydrolyzes with oxaloacetate to make citrate

Question 3

Step 2

Answer 3

• citrate is converted to isocitrate

Question 4

Step 3

Answer 4

• isocitrate is converted to alpha-ketoglutarate
• dehydrogenase reduces 1 NAD+ to 1 NADH + H+
• 1 CO2 molecule is produced

Question 5

Step 4

Answer 5

• alpha-ketoglutarate is transferred to succinyl CoA
• dehydrogenase reduces 1 NAD+ to 1 NADH + H+
• 1 CO2 molecule is produced

Question 6

Step 5

Answer 6

• succinyl CoA is hydrolyzed into succinate
• here a cycle where GDP + P are converted to GTP, which in turn, converts ADP into ATP (GTP turns into GDP +P again) and this process occurs everytime hydrolysis reaction occurs

Question 7

Step 6

Answer 7

• succinate is converted to fumarate

- dehydrogenase reduces FAD+ to FADH2

Question 8

Step 7

Answer 8

• fumarate is hydrolyzed into malate

Question 9

Step 8

Answer 9

• malate converts to oxaloacetate, and cycle begins again

- dehydrogenase reduces 1 NAD+ to 1 NADH + H+

Question 10

How is the citric acid cycle regulates?

Answer 10

• main control point is the first dehydrogenase

- when there are high [NADH + H+] levels, the activity of the enzyme is inhibited