Fatty Acid Metabolism

Question 1

Give the functions of fatty acids.

Answer 1

• energy storage & production
• structural components of membranes
• some hormones derived from fatty acids

Question 2

Describe the structure of fatty acids.

Answer 2

• carboxylic acid head group
• aliphatic side chain
• saturated = no double bonds in aliphatic side chain
• usually have even no. of C atoms

Question 3

What does TAG stand for?

Answer 3

Triacylglycerol.

Question 4

Describe lipids.

Answer 4

• highly hydrophobic, not easily transported
• in TAG ester bonds between fatty acids and glycerol
• ester linkages form between a carboxylic acid and alcohol groups by loss of water

Question 5

Give the equation for TAG breakdown in adipose tissue.

Answer 5

TAG + 3H20 > Glycerol + 3 fatty acids

Question 6

What enzyme catalyses the breakdown of TAG?

Answer 6

Triacylglycerol lipase.

Question 7

What hormone activates lipase?

Answer 7

Glucagon.

Question 8

Give the 3 steps in the oxidation of fatty acids.

Answer 8

1. Free fatty acids in the cytosol are activated forming fatty acyl-CoA
2. Fatty acyl-CoA uptake into mitochondria
3. Beta-oxidation pathway in mitochondrial mix

Question 9

What is used to transport fatty acyl CoA from cytoplasm to the mitochondrial matrix?

Answer 9

Carnitine shuttle.

Question 10

What advantage does the glyoxylate cycle have over the citric acid cycle?

Answer 10

2 extra enzymes, isocitrate lyase & malate synthase.

These allow them to bypass reactions that release CO2.

Question 11

Give the carrier involved in fatty acid synthesis.

Answer 11

ACP

Question 12

Give the cofactor involved in fatty acid synthesis.

Answer 12

NADP+

Question 13

Give the donor product for fatty acid synthesis.

Answer 13

malonyl CoA

Question 14

Give the sources of NADPH for fatty acid synthesis.

Answer 14

Pentose pathway & citrate shuttle.

Question 15

Give the first step in fatty acid synthesis.

Answer 15

1. Conversion of acetyl CoA to malonyl CoA via carboxylation
   - catalysed by acetyl CoA carboxylase
   - energy to form bonds is supplied indirectly by synthesising malonyl CoA from acetyl CoA using ATP and CO2
   - release of C)2 drives this reaction

Question 16

Give the second step in fatty acid synthesis.

Answer 16

2. Reduction of C=O group on C3 to C-OH by NADPH

Question 17

Give the third step in fatty acid synthesis.

Answer 17

3. Dehydration generates a double bond between alpha and beta carbons (C2 and C3).

Question 18

Give the fourth step in fatty acid synthesis.

Answer 18

4. Reduction of double bond to single bond.

Question 19

How is acetyl CoA tightly regulated?

Answer 19

• insulin signalling favours fatty acid synthesis, activates a phosphatase that dephosphorylates acetyl CoA carboxylase
• CoA inhibited by phosphorylation

Question 20

How are fatty acid synthesis & breakdown reciprocally regulated?

Answer 20

• glucagon promotes release of fatty acids from adipocytes, high levels of fatty acyl CoA inhibit acetyl CoA carboxylase.
• malonyl CoA inhibits carnitine acyl transferase I and prevents fatty acid oxidation by blocking entry into the mitochondrion.