Metabolism 3

Question 1

Define the role of the krebs cycle in metabolism

Answer 1

1. a way to oxidize acetyl groups (like acetyl coA) to make reduced coenzymes (like NADH and FADH) and CO2
2. oxygen is not directly involved, but is need later on to oxidize the coenzymes
3. concentrations of intermediates is not altered as the activity of the cycle increases, because its a cycle
4. occurs only in mitochondria!!

Question 2

Main sources of acetyl CoA used in the krebs cycle:

Answer 2

1. Pyruvate from glycolysis (pyruvate dehydrogenase complex converts it to acetyl CoA). inhibited by acetylcoA, ATP, NADH. AcetylcoA has a high energy thioester bond.
2. Fatty acids (go through beta oxidation to make A-coA)
3. Ketogenic amino acids

Question 3

Define the origins of the major products of the cycle

Answer 3

1. acetylcoA + oxaloacetate —- citrate
2. citrate —– isocitrate
3. Isocitrate + NAD+ ——- alpha ketoglutarate, NADH, CO2
4. alpha ketoglutarate + NAD+ + Acetyl CoA-SH ——- succinylcoA + NADH + CO2
5. Succinyl CoA + GDP —— succinate +GTP +CoA-SH
6. Succinate + FAD——– FADH2 + fumarate
7. Fumarate—–Malate
8. Malate + NAD+—– oxaloacetate + NADH

Question 4

The major products of the krebs cycle and their fate

Answer 4

1 FADH2, 3 NADH, 1 GTP —— 9 + 2 + 1 ATP (electron transport chain and oxidative phosphorylation).

Question 5

The major products of the krebs cycle and their fate

Answer 5

1 FADH2, 3 NADH, 1 GTP —— 9 + 2 + 1 ATP (electron transport chain and oxidative phosphorylation).

Question 6

inhibition and activation of pyruvate dehydrogenase

Answer 6

NADH and ATP inhibit, NAD activates

Question 7

inhibition and activation of citrate synthase

Answer 7

ATP and NADH inhibit, ADP activates

Question 8

inhibition and activation of isocitrate dehydrogenase

Answer 8

ATP and NADH inhibit, ADP activates

Question 9

inhibition and activation of alpha ketoglutarate dehydrogenase

Answer 9

ATP, GTP, NADH inhibit

Question 10

What inhibits the pyruvate dehydrogenase complex?

Answer 10

NADH, and ATP inhibit it.

Question 11

What is an interesting bond in acetyl coA?

Answer 11

High energy thioester bond

Question 12

What is the main rate limiting step in the TCA cycle?

Answer 12

Isocitrate dehydrogenase.

Question 13

What activates and inhibits isocitrate dehydrogenase?

Answer 13

activated by ADP, inhibited by ATP and NADH

Question 14

In one turn of the cycle:

Answer 14

makes 3 NADH, 1 FADH2, two CO2’s are released, 1 GTP

Question 15

The 4 main enzymes you need to know and what activates and inhibits them (see the chart)

Answer 15

Pyruvate dehydrogenase, citrate synthase, isocitrate dehydrogenase, alpha ketoglutarate.

Question 16

The 4 main enzymes you need to know and what activates and inhibits them for krebs (see the chart)

Answer 16

Pyruvate dehydrogenase, citrate synthase, isocitrate dehydrogenase, alpha ketoglutarate.