Lipid Metabolism

Question 1

What are essential fatty acids?

Answer 1

Fatty acids that humans and other animals must ingest because the body requires them for good health but cannot synthesise them

Question 2

What are essential fatty acids precursors for?

Answer 2

Eicosanoids (prostaglandins, leukotrienes, thromboxanes)

Question 3

What is cholesterol essential in the production of?

Answer 3

• Membranes - Vitamin D - Steroid hormones - Bile salts

Question 4

How does cholesterol lead to the formation of steroid hormones?

Answer 4

Cholesterol is the precursor of the five major classes of steroid hormones

Question 5

What are the 5 main classes of steroid hormones?

Answer 5

1. Androgens (e.g. testosterone) 2. Oestrogens 3. Progestogens (e.g. progesterone) 4. Mineralocorticoids (e.g. aldosterone) 5. Glucocorticoids (e.g. cortisol)

Question 6

How does cholesterol lead to the formation of bile salts?

Answer 6

Bile salts are synthesised in the liver from cholesterol

Question 7

What are chylomicrons?

Answer 7

Lipids from the diet - a droplet of fat present in the blood or lymph after absorption from the small intestine.

Question 8

Where are chylomicrons formed?

Answer 8

In intestinal epithelial cells

Question 9

Where are chylomicrons released into?

Answer 9

The lymph

Question 10

How do chylomicrons enter the circulation?

Answer 10

Via thoracic duct, into subclavian vein (Do not pass directly from the GI tract to the liver)

Question 11

Where does cholesterol in your body come from?

Answer 11

1. Synthesis (in almost all tissues but mainily in liver and intestine)
2. Diet (eggs, liver, meat)

Question 12

What is the role of lipoproteins?

Answer 12

Transport lipids such as triglycerides, phospholipids, and cholesterol

Question 13

When lipoprotein lipase breaks down triglycerides, what does it from?

Answer 13

Free fatty acids either for energy production (muscle) or storage (adipose tissue)

Question 14

Lipid pathway diagram

Answer 14

Question 15

How do fatty acids arrive at peripheral tissue?

Answer 15

1. In chylomicrons or VLDL
2. From adipose tissue

Question 16

How are fatty acids released from chylomicrons or VLDL?

Answer 16

By lipoprotein lipase

Question 17

How are fatty acids released from adipose tissue?

Answer 17

1. triacylglycerols broken down by hormone sensitive lipase
2. fatty acids released into blood
3. transported to tissues bound to albumin

Question 18

Can fatty acids be used by the brain?

Answer 18

No - cannot cross the blood brain barrier

Brain uses glucose

Question 19

What happens during fasting?

Answer 19

Fatty acids released from adipose tissue

Question 20

Describe the oxidation of fatty acids

Answer 20

1. Activation of fatty acyl CoA in cytosol (FA CoA released from CoA, attached to carnitine. Occurs on outer mit membrane)
2. Beta oxidation takes place in mitochondria (transport across membrane)
3. Long chain fatty acids require carnitine for transport

Question 21

Where does carnitine transport fatty acids?

Answer 21

Across the inner mitochondrial membrane

Question 22

What is the carnitine transport system inhibited by? What is purpose of this?

Answer 22

Malonyl CoA

Prevents sythesis and degredation of fatty acids at the same time

Question 24

Describe the spiral process of the beta oxidation of fatty acids

Answer 24

• Each turn released 1 acetyl CoA, produces NADH and FADH2
• Completely aerobic process

Question 25

What happens to the NADH and FADH2 produced by the beta-oxidation of fatty acids?

Answer 25

Oxidised by electron transport chain

Question 26

What happens to the acetyl CoA produced in the beta oxidation of fatty acids?

Answer 26

Enters Krebs cycle - producing more NADH/FADH

Question 27

What is the beta oxidation of fatty acids dependent on?

Answer 27

Also note no ATP produced by this cycle itself so entirely dependent on krebs and etc for energy production – i.e. totally dependent on oxygen

Question 28

What is fatty acid oxidation largely regulated by?

Answer 28

By access of fatty acids to the mitochondria – this is controlled by the concentration of malonyl CoA

Question 29

What is the frist step of fatty acid synthesis?

Answer 29

Malonyl CoA is formed by acetyl CoA carboxylase

Question 30

What does high [malonyl CoA] inhibit?

Answer 30

Inhibits carnitine acyl-transferase-1

This ensures that fatty acid breakdown is inhibited when energy is plentiful

Question 31

What are ketone bodies formed from?

Answer 31

Excess acetyl CoA

Question 32

Where does ketone synthesis occur?

Answer 32

In the mitochondria of liver cells under conditions where the body relies on fatty acid oxidation for energy

Question 33

When does the body rely on fatty acid oxidation for energy?

Answer 33

• Fasting
• Uncontrolled diabetes (ketoacidosis)

Question 34

Where are ketones released into?

Answer 34

Into the blood and oxidised to produce energy in peripheral issues including brain tissue

Question 35

Describe cholesterol uptake from LDL

Answer 35

1. LDL binds to receptor on cell surface and are taken up into cell
2. Cholesterol is released
3. Receptors are recycled

Question 36

What is effect of lack of receptors on cholesterol uptake from LDL?

Answer 36

Lack of receptors will prevent LDL uptake

Question 37

What is LDL receptor synthesis controlled by?

Answer 37

Level of cholesterol in cell

Question 39

What are the 4 steps of cholesterol biosynthesis?

Answer 39

1. Acetyl CoA to mevalonate (C6)
2. Mevalonate to phosphorylated isoprene units (C5) –> activation
3. Polymerise 6 isoprene units to form C30 chain (squalene)
4. Cyclisation to form ring structure (lanosterol) then cholesterol

Question 40

What stage in cholesterol biosynthesis controls the rate of synthesis?

Answer 40

1 - Acetyl CoA to mevalonate (C6)

Question 41

Where does cholesterol biosynthesis occur?

Answer 41

In cytosol and smooth endoplasmic reticulum