Week 11

Question 1

Where does the TCA cycle occur and what is its purpose?

Answer 1

Location: Mitochondrial matrix Purpose: Oxidize acetyl-CoA to CO₂ and generate NADH, FADH₂, and GTP for ATP production

Question 2

What are the overall products of 1 turn of the TCA cycle?

Answer 2

• 3 NADH • 1 FADH₂ • 1 GTP (≈ ATP) • 2 CO₂

Question 3

Which steps of the TCA cycle produce NADH?

Answer 3

• Isocitrate → α-ketoglutarate
• α-ketoglutarate → Succinyl-CoA Malate → Oxaloacetate

Question 4

Which step of the TCA cycle produces FADH₂?

Answer 4

• Succinate → Fumarate

Question 5

Which step of the TCA cycle produces GTP?

Answer 5

• Succinyl-CoA → Succinate

Question 6

Which steps of the TCA cycle release CO₂?

Answer 6

• Isocitrate → α-ketoglutarate • α-ketoglutarate → Succinyl-CoA

Question 7

Why is it called a “cycle”?

Answer 7

Because oxaloacetate is regenerated at the end to accept another acetyl-CoA

Question 8

What is the action of fluoroacetate on the TCA cycle?

Answer 8

Fluoroacetate → fluorocitrate, which inhibits aconitase, slowing the TCA cycle

Question 9

What causes Wernicke-Korsakoff syndrome (WKS)?

Answer 9

Thiamine (vitamin B1) deficiency, commonly due to chronic alcoholism

Question 10

What are the symptoms of Wernicke-Korsakoff syndrome?

Answer 10

Wernicke (acute): • Confusion • Ataxia • Ophthalmoplegia Korsakoff (chronic): • Memory loss • Confabulation • Personality changes

Question 11

What is the treatment for Wernicke-Korsakoff syndrome?

Answer 11

Immediate thiamine (B1) before glucose, plus nutrition and alcohol cessation

Question 12

What are the 3 regulatory enzymes of the TCA cycle?

Answer 12

• Citrate synthase • Isocitrate dehydrogenase • α-Ketoglutarate dehydrogenase

Question 13

How is citrate synthase regulated?

Answer 13

↓ inhibited by ATP, NADH ↑ activated by ADP

Question 14

How is isocitrate dehydrogenase regulated?

Answer 14

↓ inhibited by ATP, NADH ↑ activated by AMP, Ca²⁺

Question 15

How is α-ketoglutarate dehydrogenase regulated?

Answer 15

↓ inhibited by ATP, NADH ↑ activated by Ca²⁺

Question 16

How are vitamins involved in the Krebs cycle? (B1, B2, B3, B5)

Answer 16

B1 (thiamine): TPP for α-ketoglutarate dehydrogenase B2 (riboflavin): FAD → FADH₂ B3 (niacin): NAD⁺ → NADH B5 (pantothenic acid): part of Coenzyme A