Metabolic Pathways: Lipid Anabolism

Question 1

When are new fatty acids synthesised?

Answer 1

When body has more energy than it needs (lipogenesis)

Question 2

Where does lipogenesis occur?

Answer 2

Liver, kidney, mammary glands

Question 3

What happens when we take in excess carbohydrate?

Answer 3

Conversion to fatty acids and triglycerides in the liver

Free fatty acids are transported in plasma bound to albumin

Triglycerides formed in the liver are transported to adipose tissue by VLDL for storage

Question 4

What kind of process is lipogenesis?

Answer 4

Reductive process

Question 5

What is the substrate for lipogenesis?

Answer 5

Acetyl-CoA

Question 6

Where does lipogenesis occur?

Answer 6

Cytoplasm of liver cell

Question 7

what is the problem with acetyl-coa and lipogenesis

Answer 7

Inner mitochondrial membrane is impermeable to acetyl-coA

Question 8

What is the role of citrate?

Answer 8

Transports acetyl groups into the cytoplasm

- produced in the first step in TCA cycle

Question 9

What is the first stage of fatty acid synthesis?

Answer 9

Activation of acetyl-CoA to malonyl-CoA by acetyl-CoA carboxylase

Question 10

Where is acetyl-coa carboxylase expressed?

Answer 10

Liver and adipose tissue

Question 11

What does malonyl CoA do?

Answer 11

Donates carbon atoms to new lipid

Question 12

What is the role of fatty acid synthase

Answer 12

Catalyses synthesis of saturated long-chain fatty acids from malonyl-CoA, acetyl CoA and NADPH

Question 13

What is the structure of fatty acid synthase?

Answer 13

Dimer of identical polypeptides

Single polypeptide chain with seven distinct enzyme acitivites

Question 14

What is the important element of fatty acid synthase?

Answer 14

Contains an acyl-carrier protein (ACP)

This carries the growing fatty acid chain during synthesis

Question 15

What is the first step of fatty acid synthesis?

Answer 15

Using acetyl-CoA and malonyl-CoA as precursors, one cycle of reactions adds two carbon atoms to the growing acyl chain

• derived from malonyl-CoA
• growing acyl chain is attached to ACP

Question 16

What does the cycles of reactions require fatty acid synthase?

Answer 16

NADPH

Question 17

What is the longest length of fatty acid that can be made?

Answer 17

C-16 (palmitic)

Question 18

What enzyme has an essential role in regulating fatty acid synthesis and degradation?

Answer 18

Acetyl-CoA carboxylase

Question 19

What two levels does regulation occur at?

Answer 19

System wide mechanisms- hormones

Allosteric mechanisms

Question 20

What hormones regulate acetyl-CoA carboxylase?

Answer 20

Insulin- only released when plenty of energy, this stimulates acetyl-CoA carboxylase

Glucagon- signals starved state, switches fatty acid synthesis off

Epinephrerine- mobilise glycogen stores, inhibiting acetyl-CoA carboxylase

Question 21

Name the allosteric modulation of acetyl-CoA carboxylase

Answer 21

Palmitoyl-CoA: abundant when fatty acids are in excess, therefore antagonises it

Citrate: stimulates allosterically, high when acetyl-CoA and ATP are abundant

Question 22

What does the synthesis of triglycerides require?

Answer 22

G3P

Question 23

What produces G3P?

Answer 23

Liver, from glycerol

Adipose tissue from glucose

Question 24

When does adipose tissue produce triglycerides?

Answer 24

In the fed state-

Insulin stimulates adipose tissue uptake of glucose

Question 25

What can liver cells do to fatty acids?

Answer 25

Synthesised phospholipids, cholesterol and lipoproteins