L22 - Lipid Metabolism 2

Question 1

Why are FAs synthesised?

Answer 1

Fatty acids are synthesised for:

• Incorporation into triacylglycerols as an energy store
• Incorporation into phosphoacylglycerols for membrane synthesis

Question 2

What is the starting point for fatty acid synthesis?

Answer 2

Starting point for fatty acid synthesis is acetyl CoA which acts as a link between carbohydrate and lipid metabolism

Question 3

Where are all the C atoms in fatty acids with an even number derived from?

Answer 3

All C atoms in fatty acids with an even number of C atoms were derived from the acetate part of acetyl CoA

Question 4

Where does FA synthesis take place and what gas does it require?

Answer 4

Fatty acid synthesis takes place in the cytoplasm of eukaryotic and prokaryotic cells

Fatty acid synthesis has a requirement for CO2

Question 5

What is the name of the pathway that synthesises FAs?

Answer 5

The Malonyl Pathway

Question 6

What is the starting point for FA synthesis and where is it produced?

Answer 6

Acetyl CoA is the starting point, it is produced in the mitochondria of eukaryotic cells

Acetyl CoA must be transported from the mitochondria to the cytoplasm

Question 7

1) Acetyl CoA in the MitoMatrix is used in 2 ways, what are they?

Answer 7

1) Acetyl CoA + Carnitine ——–> Acetyl carnitine + CoASH

2) Acetyl CoA + Oxaloacetate —-> Citrate + CoASH

Question 8

What does the citrate in the MitoMatrix do?

Answer 8

Citrate

Question 9

How does the Malonyl pathway get its name?

Answer 9

The malonyl pathway gets its name because the conversion of acetyl CoA to malonyl CoA is an essential step

Question 10

What does the conversion of acetyl CoA to malonyl CoA require and what enzyme and co-enzyme is used?

Answer 10

It is this step that has the requirement for CO2 in the form of bicarbonate (H2CO3) and 1ATP

The irreversible reaction is catalysed by the enzyme acetyl CoA carboxylase

It requires the B vitamin biotin as a coenzyme

Question 11

What does ACP stand for and what B vitamin does it require?

Answer 11

• ACP stands for Acyl Carrier Protein

- It contains the B vitamin pantothenic acid

Question 12

What is the function of ACP?

Answer 12

Function of ACP is to deliver the appropriate substrate to the appropriate enzyme

Question 13

What is FAS?

Answer 13

The enzymes carrying out fatty acid synthesis are complexed together and often called fatty acid synthase (FAS)

Question 14

Describe the difference between FAS in bacteria and vertebrates

Answer 14

In bacteria each stage is catalysed by a single enzyme but all enzymes and ACP complex together to form FAS

In vertebrates there is a single very complex FAS protein which incorporates all the separate activities needed

Question 15

What enzyme is used in each case?

a) Acetyl CoA —–> Acetyl ACP
b) Malonyl CoA —–> Malonyl ACP

Answer 15

a) Acetyl transferase

b) Malonyl transferase

Question 16

How does the production of Acetyl ACP and Malonyl ACP happen together?

Answer 16

Both use a single ACP-SH molecule, and together both give off CoA to for a single CoA-SH molecule

Question 17

The malonyl pathway consists of 4 reactions, what are they?

Answer 17

1) Condensation
2) Reduction
3) Dehydration
4) Reduction

Question 18

What do both reduction reactions in the MP use as H+ donors?

Answer 18

NADPH from the pentose phosphate pathway

Question 19

State what molecule is made at each stage:

Answer 19

1) condensation
Acetyl ACP + Malonyl ACP —–> 3-keto-ACP

2) Reduction
D-3-hydroxyacyl ACP (using an NADPH)

3) Dehydration
trans Enol ACP + H2O

4) Reduction
Fatty acid ACP (using NADPH)

Question 20

How long does the malonyl pathway carry on for?

Answer 20

Normally the malonyl pathway continues until the fatty acid has 16 C atoms (palmitic acid) when it is released from ACP