Lipid synthesis and degradation (revised version)

Question 1

What are triglycerides broken down into? [2 marks]

Answer 1

• Fatty acids

- Glycerol

Question 2

What can one of the components of triglycerides be fed into? [2 marks]

Answer 2

GLYCEROL

• Glycolysis
• Gluconeogenesis

Question 3

Structure of fatty acids [3 marks]

Answer 3

• Chains of methyl groups
• Terminal carboxyl group
• Cis configuration for double bonds

Question 4

Where does fatty acid synthesis and degradation occur? [2 marks]

Answer 4

• Synthesis occurs in the cytosol

- Degradation occurs in the mitochondria

Question 5

What are the intermediates for fatty acid synthesis and degradation linked to? [2 marks]

Answer 5

• Intermediates are linked to acyl carrier proteins (ACPs) in synthesis
• Intermediates are linked to CoA in degradation

Question 6

What are added and removed in fatty acid synthesis and degradation? [2 marks]

Answer 6

• Sequential addition of 2 carbons in synthesis

- Sequential removal of 2 carbons in degradation

Question 7

What is the reductant in fatty acid synthesis? [1 mark]

Answer 7

NADPH

Question 8

What are the oxidants in fatty acid degradation? [2 marks]

Answer 8

• FAD

- NAD

Question 9

Where does NADPH for fatty acid synthesis come from? [2 marks]

Answer 9

• 60% from pentose phosphate pathway

- 40% from acetyl CoA transfer

Question 10

What is the preferred energy source for cardiac muscle? [1 mark]

Answer 10

Fats

Question 11

What is involved in acetyl CoA transfer? [4 marks]

Answer 11

• Acetyl CoA
• Oxaloacetate
• Citrate
• Malate

Question 12

What are the products of acetyl CoA transfer? [3 marks]

Answer 12

• Pyruvate
• CO2
• NADPH

Question 13

First step in fatty acid synthesis [3 marks]

Answer 13

Acetyl-CoA + ATP + HCO3- → malonyl-CoA + ADP + Pi

• acetyl-CoA carboxylase
• irreversible

Question 14

What is involved in fatty acid elongation? [4 marks]

Answer 14

• Acetyl CoA
• Malonyl CoA
• Acetoactyl-ACP
• Butyryl-ACP

Question 15

What enzyme is used in fatty acid synthesis and what is its structure? [4 marks]

Answer 15

• Fatty acid synthase
• Large and multi-enzyme
• Lots of active sites
• Dimer (makes synthesis more efficient)

Question 16

What is the first step of fatty acid synthesis activated by? [1 mark]

Answer 16

Citrate (via positive feed back)

Question 17

What is the first step of fatty acid synthesis inhibited by?

Answer 17

Palmitic acid (via negative feed back)

Question 18

Where is cholesterol synthesised? [1 mark]

Answer 18

Endoplasmic reticulum

Question 19

What is the first step of cholesterol synthesis?

Answer 19

Activation of acetate

Question 20

What is the regulatory step of cholesterol synthesis? [1 mark]

Answer 20

HMGCoA → mevalonate

Question 21

What enzyme does cholesterol inhibit? [3 marks]

Answer 21

• HMGCoA reductase
• Involved in cholesterol synthesis
• Target for statins

Question 22

Does cholesterol provide energy? [1 mark]

Answer 22

NO

Question 23

Where does fatty acid mobilisation occur and how is it mediated? [2 marks]

Answer 23

• Happens in the adipocyte

- cAMP mediated (beta 3 adrenoceptor)

Question 24

What enzyme does protein kinase activate in fatty acd mobilisation and what does this enzyme do? [2 marks]

Answer 24

• Triacylglycerol lipase

- Breaks down triglycerides into glycerol and free fatty acids

Question 25

Where does fatty acid activation (for degradation) occur? [1 mark]

Answer 25

In the liver cytosol

Question 26

What is involved in fatty acid activation (for degradation)? [3 marks]

Answer 26

- Acyl CoA - Carnitine - Acyl carnitine

Question 27

What inhibits transport of acetyl CoA from cytosol to matrix? [1 mark]

Answer 27

Malonyl-CoA (made in fatty acid synthesis)

Question 28

Where does fatty acid degradation/β-oxidation occur? [1 mark]

Answer 28

In the liver mitochondria

Question 29

What is made form the removal of 2 carbon atoms in acyl-CoA in degradation? [3 marks]

Answer 29

- FADH2 - NADH - acetyl CoA

Question 30

In what conditions does acetyl-CoA enter the citric acid cycle?

Answer 30

- Under glycolysis only | - Only in non hepatic cells

Question 31

What can acetyl-CoA form in hepatic cells? [1 mark]

Answer 31

Ketone bodies (then enter bloodstream)

Question 32

How many ATP molecules are ade from the oxidation of palmitate? [1 mark]

Answer 32

106

Question 33

What happens if the chain length of the fatty acid is odd? [2 marks]

Answer 33

- Propionyl-CoA is made | - Double bonds removed by isomerase

Question 34

Which enzymes remove even numbered double bonds? [2 marks]

Answer 34

- Reductase | - Isomerase

Question 35

What enzyme is inhibited by a low insulin/glucagon ratio? [1 mark]

Answer 35

Acetyl-CoA carboxylase

Question 36

Ketogenesis process [4 marks]

Answer 36

Acetyl-CoA → acetoacetyl-CoA → HMG-CoA → acetoacetate

Question 37

Which organs are ketone bodies a major energy source? [2 marks]

Answer 37

- Cardiac muscle | - Renal cortex

Question 38

What is insulin's negative effects on fat metabolism? [2 marks]

Answer 38

- Negative effect on breakdown | - Negative effect on β-oxidation

Question 39

What is insulin's positive effect on fat metabolism? [1 mark]

Answer 39

Fatty acid synthesis