Lecture 7 - Lipid Catabolism 2

Question 1

How many ATP does 1 glycerol molecule produce?

Answer 1

• 6 ATP from glycolysis
• 2.5 ATP from pyruvate -> acetyl-CoA
• 10 ATP from TCA cycle
• Total = 18.5 ATP

Question 2

How can monounsaturated fatty acids undergo beta-oxidation?

Answer 2

The cis bond must be converted into a trans bond by an isomerase enzyme

Question 3

Why does beta-oxidation of monounsaturated fatty acids produce less ATP?

Answer 3

1 FADH2 isn’t produced because the acyl-CoA dehydrogenase step isn’t required

Question 4

What is unique about the beta-oxidation of odd-numbered fatty acids and why does it need this?

Answer 4

• Require biotin and ATP to add an additional CO2

- CO2 is added because C3-CoA isn’t a substrate for acyl-CoA dehydrogenase

Question 5

What happens once a CO2 is added to the C3-CoA?

Answer 5

• An epimerase moves the carboxyl group from D to L configuration
• A mutase moves this to the end C making it succinyl-CoA

Question 6

What is the most common cofactor used by carboxylase enzymes?

Answer 6

Biotin

Question 7

How does biotin transfer a CO2 to a protein?

Answer 7

It forms carboxybiotin, and then transfers the carboxyl to a protein

Question 8

Which enzyme converts biotin to carboxybiotin and what is the cofactor needed?

Answer 8

• Propionyl CoA carboxylase

- ATP -> ADP; CO2

Question 9

Which enzyme converts carboxybiotin to biotin and what is the cofactor needed?

Answer 9

• Propionyl CoA carboxylase

- Propionyl CoA -> Methyl malonyl CoA

Question 10

What happens to excess Acetyl CoA that the body can’t metabolize?

Answer 10

• Converted to acetoacetate and beta-hydroxybutyrate

- Acetoacetate is converted to acetone

Question 11

Explain the ATP calculation for odd-numbered fatty acids

Answer 11

• Normally beta-oxidation for everything except the last 3
• C3 is converted to C4 which costs 1 ATP and produces succinyl-CoA
• Succinyl-CoA produces a total of 17.5 ATP (5 NADH, 2 FADH2, and 2 GTP)