Biochemistry

Question 1

How is bilirubin formed?

Answer 1

From the breakdown of RBCs.

Question 2

What is the colour of, and where are: biliverdin, urobilinogen, stercobilin.

Answer 2

Biliverdin - green, in the circulating blood, before being carried to the liver to be converted to bilirubin.
Urobilinogen - yellow, in the kidneys absorbed from the large intestine.
Stercobilin - brown colour in faeces.

Question 3

Where is bilirubin conjugated and with what other substance?

Answer 3

In the liver with glucuronic acid to make it water soluble.

Question 4

How does bilirubin travel in the blood?

Answer 4

It is non-water soluble so needs to be bound to albumin.

Question 5

What are the main uses of cholesterol in the body?

Answer 5

Synthesis of Vitamin D
Manufacture of bile salts.
Steroid hormone synthesis.

Question 6

What enzyme is involved in the production of cholesterol?

Answer 6

HMG-CoA. This is a product of Acetyl CoA and is the rate-limiting step.

Question 7

What is required to make one molecule of cholesterol?

Answer 7

18 moles of Acetyl CoA, 36 moles of ATP and 16 moels of NADPH.

Question 8

What are VLDLs? Where are they produced? What do they do?

Answer 8

Very low density lipoproteins; produced by the liver; transport of lipids, delivers triglycerides to cells.

Question 9

What are LDLs? What do they do?

Answer 9

Low density lipoproteins. Carries cholesterol to cells that need it. Bad cholesterol.

Question 10

What are HDLs? Where is it produced? What does it do?

Answer 10

High density lipoproteins; Produced in the liver and intestines; good cholesterol which carries cholesterol from the cells to the liver. Can inhibit inflammation, activation of the endothelium, coagulation and platelet aggregation.

Question 11

What is the main component of VLDLs, LDLs and HDLs?

Answer 11

VLDL - TG
LDL - Cholesterol
HDL - protein

Question 12

What is the life span of a RBC?

Answer 12

120 days.

Question 13

What is needed for the conjugation of bilirubin in the liver?

Answer 13

Glucuronic acid.

Question 14

What enzyme is involved in the conversion of harm —> biliverdin?

Answer 14

Haem oxygenase, a CYP450 enzyme

Question 15

What percentage of bilirubin is derived from the breakdown of Hb?

Answer 15

75%

Question 16

What is the normal concentration of bilirubin?

Answer 16

21umol/L

Question 17

What is the benefit of conjugating bilirubin?

Answer 17

It makes it water soluble, so it is able to be excreted in the bile.

Question 18

What percentage of cholesterol synthesis occurs in the liver and what percent in the peripheral tissue?

Answer 18

80% in liver

20% in peripheral tissue.

Question 19

What is the rate limiting step in cholesterol synthesis?

Answer 19

The expression levels and activity of HMG-CoA reductase (enzyme which regulates cholesterol synthesis).

Question 20

Where are primary bile acids synthesised and what is the rate limiting step?

Answer 20

Choline and chenodeoxycholic acids, the primary bile acids, are synthesised in hepatic parenchymal cells. The rate limiting step is the reaction catalysed by alpha hydroxylase, which introduces a hydroxyl group at the alpha-7 position.

Question 21

What is the ratio of glycine bile conjugated and taurine bile conjugated?

Answer 21

Glycine 3 : taurine 1

Question 22

Describe the classic pathway of bile synthesis from cholesterol.

Answer 22

Cholesterol is hydroxylised at the 7 position via the action of cholesterol 7-alpha hydroxylase (CYP7A1), which is an ER localised enzyme, CYP7A1 is a metabolic enzyme.

Question 23

What percentage of cholesterol is excreted?

Answer 23

50%

Question 24

Which lipoproteins carry cholesterol to peripheral tissue from liver and which carry cholesterol from tissue to liver?

Answer 24

LDL and VLDL carry cholesterol —> peripheral tissue.

HDL —> liver.

Question 25

What is the role of apolipoproteins?

Answer 25

Apolipoproteins facilitant lipid solubilisation and help to maintain the structural integrity of lipoproteins.
They serve as a ligand for lipoprotein receptors and regulate activity of enzymes involved in lipoprotein catabolism.

Question 26

What is the protein that can result in exchange of cholesterol ester or triglycerides to change the lipoprotein class?

Answer 26

Cholesterol ester transfer protein (CETP)

Question 27

How does cholesterol and TGs get to be free fatty acids and glycerol?

Answer 27

Dietary TGs and cholesterol enter circulation in chylomicrons which are acted upon by lipoprotein lipase to become —> glycerol and fatty acids and can be delivered to peripheral tissue.