Fatty Acid Metabolism

Question 1

Describe the steps in fatty acid oxidation

Answer 1

1. Activation
2. Transport into mitochondria
3. B-oxidation cycle

Question 2

Describe fatty acid activation

Answer 2

Occurs in the cytosol.
A free fatty acid is converted into fatty acyl-CoA using the enzyme Acyl-CoA synthetase.
The reaction uses 2 high energy phosphate bonds: ATP into AMP + PPi
It is made irreversible by rapid hydrolysis of pyrophosphate.

Question 3

Describe the transport of acyl-CoA into mitochondria

Answer 3

The fatty acyl-CoA can’t cross the mitochondrial membrane directly.
1. Acyl-CoA attaches to Carnitine using the enzyme Carnitine Palmitoyltransferase 1 (CPT-1), forming fatty acyl-Carnitine.
2. Fatty acyl-carnitine is then transported into the mitochondrial matrix.
3. CPT-2 transfers the acyl group back from Carnitine to CoA, reforming fatty acyl-CoA.

Question 4

Describe the steps in the B-oxidation cycle

Answer 4

1. Fatty acyl-CoA into trans-🔺^2-enoyl-CoA using enzyme Acyl-CoA dehydrogenase. FAD is reduced to FADH2.
2. Trans-🔺^2-enoyl-CoA into L-3-hydroxyacyl-CoA using enzyme Enoyl-CoA hydratase. Water is added.
3. L-3-hydroxyacyl-CoA into 3-ketoacyl-CoA using enzyme L-3-hydroxyacyl-CoA dehydrogenase. NAD+ is reduced to NADH.
4. 3-ketoacyl-CoA into Fatty acyl-CoA + Acetyl-CoA using enzyme B-ketothiolase

Question 5

What additional reactions to unsaturated fatty acids require ?

Answer 5

1. Isomerase
2. Reductase to get rid of the double bonds

Question 6

What do odd chain fatty acids require ?

Answer 6

1. Carboxylation to get rid of extra carbons from Propionate CoA
2. Isomeration to turn it into something we can get energy out of- succinate which goes into the Krebs cycle

Question 7

What vitamin is need for odd chain fatty acids ?

Answer 7

Vitamin B12

Question 8

Where is the main site of ketone production?

Answer 8

liver

Question 9

What cells use ketones in preference to glucose ?

Answer 9

The heart
The renal medulla

Question 10

What ketones are made from acetyl-CoA ?

Answer 10

1. Acetoacetate
2. D-3-Hydroxybutyrate
3. Acetone

Question 11

Describe the steps in fatty acid synthesis

Answer 11

1. Transport of Acetl-CoA to cytoplasm
2. Carboxylation to Malonyl-CoA
3. Fatty acid synthase complex

Question 12

Describe the transport of Acetyl-CoA in fatty acid synthesis

Answer 12

1. Acetyl-CoA combines with Oxaloacetate to form citrate using the enzyme citrate synthase.
2. Citrate is transported out of mitochondria
3. Citrate is then converted back into Acetyl-CoA and Oxaloacetate via the enzyme ATP-citrate lyase
4. Malate dehydrogenase converts Oxaloacetate into malate which is then converted into Pyruvate
5. Pyruvate is transported back into mitochondria

Question 13

Describe the Carboxylation step of fatty acid synthesis

Answer 13

Acetyl-CoA is turned into Malonyl-CoA using enzyme Acetyl CoA carboxylase

Question 14

What activates Acetyl-CoA carboxylase ?

Answer 14

Insulin
Citrate

Question 15

What inhibits the Acetyl-CoA carboxylase ?

Answer 15

Glucagon
Epinephrine

Question 16

Describe the fatty acid synthase complex step

Answer 16

1. Acetyl-CoA is transferred to the acyl carrier protein (ACP)
2. Malonyl-CoA is loaded onto the ACP
3. Condensation reaction: Malonyl-CoA into Acetoacetyl ACP
4. Reduction reaction: Acetoacetyl CoA into B-hydroxbutyryl ACP using enzyme B-ketoacyl ACP reductase. NADH is a reducing agent.
5. Dehydration reaction: B-hydroxbutyryl ACP into Crotonyl ACP using enzyme 3-hydroxyl yo ACP dehydratase
6. Reduction reaction: Crotonyl ACP into Butyryl ACP using enzyme Enoyl ACP reductase

Question 17

When does fatty acid synthase stop ?

Answer 17

When it reaches 16C Palmitate

Question 18

What are the names of some lipoproteins?

Answer 18

1. Chylomicrons- from intestine
2. VLDL- transports lipids made in the liver
3. LDL- cholesterol to tissue
4. HDL- cholesterol to liver