Fatty acids

Question 1

What is beta-oxidation?

Answer 1

Metabolising fatty acids in the mitochondria, usually during fasting over long time periods

Question 2

What is thiolysis?

Answer 2

S-H bond breaking as 1 compound is cleaved into 2: acetyl CoA and the fatty acyl CoA (now 2 carbons shorter)

Question 3

What first happens in beta-oxidation to the fatty acid, and where?

Answer 3

In the outer mitochondrial membrane, the fatty acid + ATP+ HS-CoA, using acyl CoA synthetase, makes acyl CoA, AMP and PPi

Question 4

Why is the thioester bond of acyl CoA useful?

Answer 4

This bond is strong but unstable, so can form acetyl CoA

Question 5

What is the fate of acetyl CoA produced?

Answer 5

If carbohydrate metabolism and fatty acid metabolism are balanced (as oxaloacetate is needed for entry), acetyl CoA will enter the TCA cycle

Question 6

What happens to the fatty acyl CoA formed from fatty acids?

Answer 6

It couples with cartinine- acyl cartinine can move into the mitochondrial matrix using a translocase enzymes

Question 7

What does the translocase enzyme do?

Answer 7

Moves 1 substance into the matrix (acyl cartinine) and another out (the cartinine)

Question 8

What happens to the acyl CoA, once in the mitochondrial matrix?

Answer 8

Dehydrogenation, forming 1 FADH2, hydration, oxidation, forming 1 NADH, then thiolysis

Question 9

How many times does the beta-oxidation cycle repeat?

Answer 9

After thiolysis, the 2 carbon acetyl CoA is removed leaving the 2 carbon shorter fatty acyl CoA chain. This cycle continues until a 4C fatty acyl CoA chain remains. 2 acetyl-CoA molecules are made from this.

Question 10

Deficiency of cartinine: inheritance and problems

Answer 10

Autosomal recessive; gene which encodes the transporter is mutated so less cartinine is taken up–> supplements can be taken

Question 11

When does beta-oxidation dominate as a process? What happens during this?

Answer 11

During fasting- acetyl CoA is used to make ketone bodies e.g. acetone

Question 12

What is fatty acid biosynthesis?

Answer 12

Lipogenesis: A process which occurs in the cytoplasm of the liver, adipose tissue and lactating breast

Question 13

What occurs during fatty acid biosynthesis/lipogenesis?

Answer 13

Decarboxylation condensation reactions (so water and CO2 formed) involving acetyl CoA and acyl CoA (any length). Joining the two chains together causes elongation, and this compound is reduced and hydrated. The fatty acyl group linked to an acyl carrier protein (ACP)

Question 14

What is the difference between beta oxidation & fatty acid biosynthesis?

Answer 14

Beta oxidation: mt matrix, coenzymes FAD/NAD+ used, CoA carrier
Lipogenesis: cytoplasm, 2 enzymes only, coenzyme NADP, ACP carrier

Question 15

In beta-oxidation, what enzymes are used during the first stage of the cycle?

Answer 15

Acyl CoA dehydrogenases in the mt matrix; a variety are used as each binds to the FA acyl CoA chains of varying lengths (due to 2C removed per cycle). This ensures the substrate is still recognised

Question 16

What disorders of beta-oxidation can occur?

Answer 16

Medium chain acyl-coenzyme A dehydrogenase deficiency (MCADD)- autosomal recessive mainly in Caucasians which can be fatal if undiagnosed- cannot fully oxidise fatty acids

Question 17

What are treatments of MCADD?

Answer 17

Never go without food for more than 10-12 hours, high carb diet (can cause appetite loss) and to prevent dependency on FAs, i.v. glucose administered

Question 18

What happens if the fatty acids we consumed are of an odd length?

Answer 18

A 4C chain will not occur after repeats of the cycle, but the 3C proprionyl-CoA can undergo reactions to form succinyl-CoA. This can enter the TCA cycle