LESSON 10 : CITRIC ACID CYCLE

Question 1

Oxidation of Acetyl-CoA Yields different energy currencies Also known as

Answer 1

Krebs cycle, Tricarboxylic acid cycle

Question 2

Step 1: Combination of Acetyl-CoA and Oxaloacetate

Answer 2

• Enzyme: Citrate Synthase
• Acetyl-CoA (2C)combines with Oxaloacetate (4C), water is introduced
• Result: 6-carbon Citrate, CoASH

Question 3

Step 2: Citrate is converted to Isocitrate

Answer 3

• Enzyme: Aconitase
• Process: Isomerization
• Result: Isocitrate, Isomer of Citrate

Question 4

Step 3: Oxidative decarboxylation of Isocitrate

Answer 4

• Enzyme: Isocitrate dehydrogenase
• Process: Oxidative decarboxylation
- Isocitrate is oxidized by NAD+
- Isocitrate loses a carboxyl group
• Product: alpha- ketoglutarate (5C), Carbon Dioxide,NADH

Question 5

Step 4: Oxidative decarboxylation of a-ketoglutarate

Answer 5

• Enzyme: a-ketoglutarate
dehydrogenase
• Process: Oxidative decarboxylation
• CoA from CoA-SH is picked up by a- ketoglutarate during the process
• Product: Succinyl CoA (4C), NADH, CO2

Question 6

Step 5:Formation of Succinate

Answer 6

• Enzyme: succinyl-CoA synthetase
• Process: Substrate level phosphorylation •Hydrolysis of CoA gives energy to phosphorylate GDP to GTP

1 GTP = 1 ATP
Product: Succinate, CoASH,GTP

Question 7

Step 6:Oxidation of Succinate

Answer 7

Enzyme: Succinate dehydrogenase
Process: Oxidation
FAD oxidizes Succinate Product: Fumarate, FADH2 FADH2 - Flavin adenine dinucleotide; similar function to NADH

Question 8

Step 7:Hydration of Fumarate

Answer 8

• Enzyme: Fumarase
• Process: Hydration
• Water is added to Fumarate
• Product: Malate

Question 9

Step 8:Oxidation of Malate

Answer 9

• Enzyme: Malate dehydrogenase
• Process: Oxidation
• NAD+ oxidizes Malate
• Product: Oxaloacetate, NADH

Question 10

What to do with NADH,FADH2 and GTP?

Answer 10

• NADH,FADH2 are electron carriers who will proceed to ETC to make more ATP
• GTP will be converted to ATP

Question 11

Products (per Acetyl-CoA)

Answer 11

• 3 NADH
• 1 FADH2
• 1 GTP
• 2CO2 (By-product)

Question 12

Conversion rates (Pyruvate oxidation to Krebs cycle)

Answer 12

1 NADH = 2.5 ATP
1 FADH2 = 1.5 ATP
1 GTP = 1 ATP

Question 13

TO SUMMARIZE

Answer 13

GLYCOLYSIS
2 ATP
2 NADH

PYRUVATE OXIDATION
2 NADH (Since 2 molecules of Pyruvate)

CITRIC ACID CYCLE
6 NADH (Since 2 molecules of Acetyl-CoA)
2 FADH2
2 GTP