Unit 7 - Kreb Cycle

Question 1

Enzyme used for reaction 1 of the Kreb Cycle?

Answer 1

Citrate Synthase

Question 2

Products of reaction 1 of the Kreb Cycle?

Answer 2

Citrate, CoA-SH (Coenzyme A)

Question 3

What is a synthase?

Answer 3

Enzyme that catalyzses SYNTHESIS reactions without ATP or GTP

Question 4

What is a synthetase?

Answer 4

Same as synthase, but directly requires ATP or GTP

Question 5

What happens in reaction 1 of the Kreb Cycle?

Answer 5

Acetyl-CoA & Oxaloacetate form Citrate

Question 6

What happens in reaction 2 of Kreb Cycle?

What drives reaction 2?

Answer 6

Citrate reversibly forms isocitrate from citrate

Driven by irreversibility of steps 1 and 3

Question 7

Enzyme used in reaction 2 of Kreb Cycle?

Answer 7

Aconitase

Question 8

What happens in step 3 of Kreb cycle?

Reversibility?

Answer 8

Isocitrate is irreversibly oxidized & decarboxylated to alpha-ketoglutarate irreversibly

Question 9

Enzyme used in step 3 of Kreb cycle?

Answer 9

Isocitrate dehydrogenase

Question 10

Products formed in step 3 of Kreb cycle?

Answer 10

Alpha-ketoglutarate, NADH, and CO2 (from oxaloacetate, not the acetyl-coa component)

Question 11

What happens in step 4 of Kreb cycle?
Revesibility?

Answer 11

α-ketoglutarate (bound to CoASH) is oxidized & decarboxylated to succinyl-CoA

Irreversible

Question 12

Enzyme used in step 4 of Kreb cycle?
Products?

Answer 12

α-ketoglutarate dehydrogenzse complex

Succinyl-CoA, NADH, CO2 (from oxaloacetate again, like in step 3)

Question 13

By what mechanism does the α-ketoglutarate complex follow?

Answer 13

Essentially the same as the pyruvate dehydrogenase complex, with thiamine pyrphosphate, lipoyllysine oxidation and reduction, and the dehydrogenase of lipoyllysine using NAD+

Question 14

What happens in step 5 of kreb cycle?

REversibility?

Answer 14

Succinyl-CoA is converted to succinate reversibly

Question 15

Enzyme used in step 5 of kreb cycle?

Products?

Answer 15

Succinyl-CoA Synthetase (*named after reverse reaction)

GTP, CoA-SH

Question 16

What happens in step 6 of kreb cycle?

Reversibility?

Answer 16

Succinate is reversibly converted to fumarate

Question 17

Enzyme used in step 6 of kreb cycle?

Products?

Answer 17

Succinate dehydrogenase

FADH2, Fumarate

Question 18

What happens in step 7 of Kreb cycle?

Reversibility?

Answer 18

Fumarate reversibly converted to L-malate

Question 19

Enzyme used in step 7 of Kreb cycle?

Products?

Answer 19

Fumarase (essentially adds water to C=C bond)

L-Malate

Question 20

What happens in Step 8 of Kreb Cycle?

Reversibility?

Answer 20

Convert L-matae to oxaloacetate reversibly

Question 21

Enzyme used in Step 8 of Kreb Cycle?

Products?

Answer 21

L-malate dehydogenase

NADH, Oxaloacetate

Question 22

What is the overall reaction of Kreb cycle?

Answer 22

Question 23

What molecules regulate Kreb cycle and at what steps?

*draw cycle, label regulators, and the type of regulation (where applicable)

Answer 23

Reaction 1 - Citrate Synthase

• Increase in NADH - INHIBIT
• Increase in ADP - activate
• Increase in citrate - INHIBIT (Product inhibition)
• Increase in ATP - INHIBIT
• Increase in Succinyl-CoA - INHIBIT (Feedback Inhibition)

Reaction 3 - Isocitrate dehydrogenase

• Increase in in ATP - Inhibit
• Increase in NADH - Inhibit
• Increase in ADP - Activate
• Increase in Ca2+ - Activate (muscle usage)

Reaction 4 - α-ketoglutarate dehydrogenase complex

• Increase in ATP - inhibit
• Increase in NADH - inhibit
• Increase in Succinyl-CoA - INHIBIT (Product inhibition)
• Incrase in Ca2+ - Activate