Fatty Acid Metabolism (beta-oxidation)

Question 1

Summarise the metabolism of glycerol in the liver.

Answer 1

Enters the glycolysis pathway by conversion into glucose by gluconeogensis.

Question 2

Summarise the metabolism of glycerol in most tissue.

Answer 2

Enters the glycolysis pathway where its converted to pyruvate which enters the TCA cycle.

Question 3

Where in the cell does β-oxidation of fatty acids occur?

Answer 3

In the Mitochondrial matrix

Question 4

How many reactions occur in β-oxidation?

Answer 4

Four

Question 5

How are long chain fatty acids activated?

Answer 5

Reaction with CoA to form a thiol ester (fatty acyl CoA). Requires ATP.
RCOO- + ATP + CoA-SH > RCO-S-CoA + AMP +2Pi

Question 6

What system transports fatty-acyl CoA into the mitochondrial matrix?

Answer 6

The carnitine shuttle system

Question 7

What is the biochemical role of carnitine?

Answer 7

Transport of fatty-acyl CoA into the mitochondrial matrix.

Question 8

By what mechanism does carnitine transport fatty-acyl CoA into the mitochondrial matrix?

Answer 8

Carnitine + fatty-acyl CoA > carnitine-acyl complex + CoA(catalysed by carnitine transferase I)

carnitine-acyl complex is transport into mitchondrial matrix through transporter proteins.

carnitine acyl complex is reacted with CoA to reform the fatty-acyl CoA and release carnitine. Catalysed by carnitine transferase II

Question 9

What enzyme catalyses the cytosolic reaction of carnitine + fatty-acyl CoA to form the carnitine-acyl complex?

Answer 9

Carnitine transferase I

Question 10

What enzyme catalyses the reaction in the mitochondrial matrix that release carnitine and regenerates fatty-acyl CoA?

Answer 10

Carnitine transferase II

Question 11

Name the 4 stages of β-oxidation in order.

Answer 11

1. Oxidation
2. Hydration
3. Oxidation
4. Thiolysis

Question 12

Describe the first stage in β-oxidation of fatty acids.

Answer 12

Oxidation:  alkane > alkene
Fatty-acyl CoA > Enoyl-CoA
-CH2-CH2- > -HC=CH-
FAD  >  FADH2
Catalysed by acyl-CoA dehydrogenase.

Question 13

Describe the second stage in β oxidation of fatty acids.

Answer 13

Hydration: alkene > alcohol
Enoyl-CoA > Hydroxyacyl-CoA
-HC=CH- > -CHOH-CH2-
Catalysed by Enoyl-CoA hydratase

Question 14

Describe the third stage in β oxidation of fatty acids.

Answer 14

Oxidation: alcohol > ketone
Hydroxyacyl-CoA > Ketoacyl CoA
-CHOH-CH2-  >  -C=O-CH2
NAD+  >  NADH
Catalysed by Hydroxyacyl-CoA dehydrogenase

Question 15

Describe the forth stage of β oxidation of fatty acids.

Answer 15

Thiolysis: (using CoA)
Ketoacyl CoA > Fatty-acyl CoA + acetyl CoA
Catalysed by β-ketoacyl-CoA thiolase

Question 16

What happens to the acetyl CoA produces in β-oxidation?

Answer 16

Enters the TCA cycle.

Question 17

What happens to the fatty-acyl CoA that is produced in β-oxidation?

Answer 17

Re-enters the beta-oxidation pathway to produce acetyl CoA. 2 carbons removed each round.

Question 18

What happens to odd chain fatty acids?

Answer 18

Broken down until 3 carbon propionyl CoA remains. Propionyl CoA is broken down to succinate CoA which enters the TCA cycles.

Question 19

What is the 3 carbon product of breakdown of odd chain fatty acids?

Answer 19

Propionyl- CoA

Question 20

What enzyme catalyses the oxidation of fatty-acyl CoA to Enoyl-CoA?

Answer 20

acyl-CoA dehydrogenase

Question 21

What enzyme catalyses the hydration of Enoyl-CoA to Hydroxyacyl-CoA?

Answer 21

Enoyl-CoA hydrolase

Question 22

What enzyme catalyses the oxidation of Hydroxyacyl-CoA to Ketoacyl-CoA?

Answer 22

Hydroxyacyl-CoA dehydrogenase

Question 23

What enzyme catalyses the thiolysis of Ketoacyl-CoA into a fatty-acyl CoA and acetyl CoA with the addition of CoA?

Answer 23

β-Keto-acyl CoA thiolase

Question 24

What would be the energy yield of a 16 carbon fatty acid?

Answer 24

-2 ATP for activation to form the fatty-acyl CoA

Forms 8 acetyl CoA molecules
Each produces 10 ATP
8x10 = +80 ATP

β-oxidation pathway = 1FADH2 + 1NADH
FADH2 = 2 ATP
NADH = 3 ATP

7 repeats of β-oxidation pathway = 5x7
=35 ATP

Total: -2+80+35 = 113 ATP

Question 25

What activates lipase (release of fatty acids from adipose)?

Answer 25

Adrenaline and glucagon

Question 26

Outline the importance of triacylglycerides as an energy store in the body.

Answer 26

Compact storage
Large body stores
High energy yield