Energy Production Lipids

Question 1

What elements do lipids usually contain?

Answer 1

Most only contain C, H, O but phospholipids contain P and N

Question 2

Why do lipids release more energy than carbohydrates?

Answer 2

They are more reduced than carbohydrates so release more energy when oxidised - more H atoms released for oxidative phosphorylation

Question 3

3 classes of lipids

Answer 3

1. Fatty acid derivates
2. Hydroxyl-methyl-glutaric acid derivates (C6)
3. Vitamins

Question 4

Fatty acid derivatives (4)

Answer 4

Fatty acids - fuel molecules
Triacylglycerols - fuel and insulation
Phospholipids - membrane
Eicosanoids - local mediators (chemical messenger molecule)

Question 5

Hydroxyl-methyl-glutaric acid derivates (4)

Answer 5

Ketone bodies - water soluble fuel molecules
Cholesterol
Cholesterol esters - cholesterol storage
Bile acids and salts - lipid digestion

Question 6

Why are triacylglycerols stored in an anhydrous form?

Answer 6

They are hydrophobic

Question 7

What are triacylglycerols?

Answer 7

Storage molecules in adipose tissue until it needs to be metabolised

Question 8

When are triacylglycerols utilised

Answer 8

Prolonged exercise, starvation and during pregnancy

Question 9

Hormonal control of triacylglycerols

Answer 9

Glucagon mobilises the fat
Insulin stimulates storage of fat

Question 10

What is esterification

Answer 10

The process of triacylglycerol formation from glycerol and fatty acids

Question 11

What happens to triacylglycerol in the GI tract in stage one of metabolism?

Answer 11

Pancreatic lipases digest lipid into fatty acids and glycerol

Question 12

Explain what happens to fatty acids after TAG is hydrolysed (5)

Answer 12

1. Fatty acids are converted back to TAG in epithelial cells of small intestine
2. Packaged into lipoprotein molecules called chylomicrons
3. Released into circulation via lymphatic
4. Carried to adipose tissue
5. Stored as triglyceride

Question 13

How does stored TAG in adipose tissue get to consumer tissues when needed?

Answer 13

Released as fatty acids and carried in the blood to tissues as albumin-fatty acid complex where they are released to tissues and oxidised for energy

Question 14

Explain the triglyceride/ fatty acid cycle in adipose tissue (3)

Answer 14

1. Glycerol-1-P from glucose and Fatty acrylic-coA go through esterification to make triglyceride
2. Triglyceride constantly breaks down
3. All glycerol released, some fatty acids released into blood on albumin and others are reactivated to fatty acyl-CoA to join with glycerol again and continue the cycle

Question 15

What happens to the triglyceride/fatty acid cycle when glucose levels fall?

Answer 15

1. G-1-P production is reduced so not put into the cycle
2. Nothing for fatty acyl-CoA to re-esterify with to make triglyceride
3. Triglyceride continues breaking down and fatty acids only released into blood on albumin to supply tissues

Question 16

General formula for fatty acids

Answer 16

CH3(CH2)nCOOH

Question 17

Why are certain polyunsaturated fatty acids essential in the diet?

Answer 17

Mammals can’t synthesise them because they can’t introduce a double bond past carbon 9

Question 18

Summary of fatty acid catabolism (3)

Answer 18

1. FA activated (by linking to coenzyme A in the cytoplasm)
2. Transported across the inner mitochondrial membrane using a carnitine shuttle
3. FA go through a series of oxidative reaction (FAD to FAD2H) with C2 removed each cycle