Session 2 - Lipids

Question 1

Why do lipids release more energy than carbohydrates?

Answer 1

Lipids are more reduced than carbohydrates - release more energy when oxidised

Question 2

What are the three classes of lipids?

Answer 2

1. Fatty acid derivatives
2. Hydroxy-methyl-glutaric acid derivatives (C6 compound)
3. Vitamins

Question 3

Which lipids are classed as fatty acid derivatives? (4)

Answer 3

1. Fatty acids
2. Triacylglycerols (triglycerides)
3. Phospholipids
4. Eicosanoids

Question 4

Which lipids are classed as HMG derivatives? (4)

Answer 4

1. Ketone bodies
2. Cholesterol
3. Cholesterol esters
4. Bile acids and salts

Question 5

Which vitamins are classed as lipids?

Answer 5

A, D, E, K

Question 6

How are TAGs formed?

Answer 6

Esterification

3 Fatty acids + glycerol

Question 7

When are TAGs utilised? (3)

Answer 7

1. Prolonged exercise
2. ‘Starvation’
3. Pregnancy

Question 8

Which hormone promotes storage of TAGs?

Answer 8

Insulin

Question 9

Which hormones reduce storage of TAGs? (5)

Answer 9

1. Glucagon
2. Adrenaline
3. Cortisol
4. Growth hormone
5. Thyroxine

Question 10

How are fatty acids transported in the blood?

Answer 10

Packaged in chylomicrons - lipoproteins

Question 11

Where in the body are TAGs metabolised? Which enzyme hydrolyses TAGs?

Answer 11

GI tract (small intestine), extracellular hydrolysis of lipids
- pancreatic lipases

Question 12

Where in the body/to which cells are lipids not transported to?

Answer 12

Brain - fatty acids can’t pass the blood brain barrier

RBCs - no mitochondria

Question 13

How does fat mobilisation take place?

Answer 13

Hormone-sensitive lipase hydrolyses TAGs in adipose tissue to release fatty acids and glycerol - lipolysis
- the FAs are carried to tissues vie the bloodstream bound to albumin

Question 14

List the events in the fatty acid cycle.

Answer 14

1. Fatty acids converted to fatty acyl-CoA
2. Fatty acyl-CoA combines with glycerol-1-P from glycolysis to form triglycerides
3. Triglycerides get hydrolysed to fatty acids and glycerol

Question 15

What changes does early starvation cause to the fatty acid cycle in adipose tissue?

Answer 15

Early starvation - low extracellular [glucose] acts as a signal and results in fatty acid release as an alternative fuel

• no source glycerol-1P to form triglycerides
• triglycerides broken down to fatty acids and glycerol
• fatty acids released with albumin
• glycerol transported to liver

Question 16

What are unsaturated fatty acids?

Answer 16

Fatty acids containing one or more double bonds

Question 17

Which fatty acids are essential for mammals?

Answer 17

Certain polyunsaturated fatty acids

Question 18

Why are certain polyunsaturated fatty acids essential in mammals?

Answer 18

Mammals cannot introduce a double bond beyond C9

Question 19

Where does fatty acid catabolism take place?

Answer 19

Mitochondria

Question 20

What are the three stages of fatty acid catabolism?

Answer 20

1. Activation of fatty acid by linking to Coenzyme A (outside mitochondria)
2. Carnitine shuttle transports across inner mitochondrial membrane
3. Oxidative reactions with C2 removed each cycle

Question 21

Which enzyme is involved in fatty acid activation?

Answer 21

Fatty acyl CoA synthase

Question 22

How does carnitine shuttle fatty acids across the inner mitochondrial membrane into the matrix?

Answer 22

1. CAT1 adds Acyl from Acyl-CoA to Carnitine -> Acyl Carnitine
2. Carnitine shuttle transporter transports acyl carnitine into the matrix
3. CAT2 removes acyl