Post-absorption processing of fats.

Question 1

Cholesterol is a precursor for:

Answer 1

Bile salts, steroid hormones, vitamin D and membranes

Question 2

Where are chylomicrons formed? Where are they released?

Answer 2

Intestinal epithelial cells. Released into lymph.

Question 3

How do fatty acids arrive at peripheral tissues?

Answer 3

In chylomicrons/VLDL (released by lipoprotein lipase). From adipose tissue (broken down by hormone-sensitive lipase, transported bound to albumin).

Question 4

What is the first step of fatty acid oxidation?

Answer 4

Activation to fatty acyl CoA in cytosol.

Question 5

Where does the oxidation of fatty acids take place?

Answer 5

Mitochondria

Question 6

What is required for the transport of long-chain fatty acids?

Answer 6

Carnitine and carnitine carrier protein - transports them across mitochondrial inner membrane.

Question 7

What is produced from the oxidation of fatty acids?

Answer 7

Acetyl CoA - Krebs cycle

NADH and FADH - oxidised by electron transport chain

Question 8

How many molecules of ATP are produced from the oxidation of one fatty acid?

Answer 8

108

Question 9

What controls fatty acid metabolism?

Answer 9

Regulated by access of fatty acids to the mitochondria - controlled by conc. of malonyl CoA (produced by 1st step of fatty acid synthesis). Inhibits breakdown when energy is plentiful.

Question 10

What are ketone bodies formed from?

Answer 10

Excess acetyl CoA

Question 11

Where does the synthesis of ketone bodies occur?

Answer 11

Mitochondria of liver cells when body is fasting or during diabetes.

Question 12

What is the most important step in cholesterol biosynthesis?

Answer 12

1st - acetyl CoA to mevalonate

Question 13

How is cholesterol synthesis controlled?

Answer 13

Adjusting the activity or amount of HMG CoA reductase - controlled by cholesterol levels and energy levels.

Question 14

What is the effect of insulin of HMG-CoA reductase

Answer 14

Stimulation (via dephosphorylation)

Question 15

What effect do saturated fats have on lipoprotein levels?

Answer 15

Increase LDL

Question 16

What effect do trans fats have on lipoprotein levels.

Answer 16

Can raise LDL and lower HDL

Question 17

What is the aetiology of familial hypercholesterolaemia?

Answer 17

Lack of LDL receptors.

Question 18

How does cholesterol contribute to the negative feedback loop that contributes to a reduction in the txn of HMG-CoA reductase (hence reduction in cholesterol synthesis).

Answer 18

Inhibits txn-enhancing signal.

Question 19

Why is HDL considered ‘good cholesterol’?

Answer 19

Involved in reverse cholesterol transport - returning cholesterol from peripheral cells to the liver.

Question 20

What is the initiating factor in atherosclerosis?

Answer 20

Damage to endothelial cells allows LDL to access subintimal space.

Question 21

What happens to subintimal LDL to contribute to atherosclerosis?

Answer 21

Becomes oxidised and is internalised by macrophages. Accumulation of foam cells create bulge in vessel wall - atherosclerotic plaque. Fibrous collagen cap forms.

Question 22

Why might an atherosclerotic plaque rupture?

Answer 22

There is a continued inflammatory response - induces macrophages to produce proteinase enzymes which degrade the fibrous cap.

Question 23

What is the cause of alcoholic steatohepatitis?

Answer 23

Metabolism of large amounts of alcohol inhibits fatty acid oxidation and activated excess triglyceride synthesis (caused by high NADH).

Question 24

What is the cause of non-alcoholic steatohepatitis?

Answer 24

Insulin resistance leads to increased insulin secretion - stimulates fatty acid synthesis.