Cholesterol

Question 1

What is cholesterol?

Answer 1

Steroid composed of 27 carbon atoms

Question 2

What is the structure of cholesterol?

Answer 2

Cyclic rings w hydrophobic tail.
Planar
Very hydrophobic (only carbon and hydrogen atoms) other than at position 3 where there is a hydroxyl group

Question 3

Where is most of the cholesterol in our body?

Answer 3

> 90% in our cell membranes ( vital component of cell membranes )

Question 4

What can cholesterol do in the membrane?

Answer 4

It can increase and decrease membrane stiffness depending on the temperature (maintains fluidity and mechanical stability of the membrane)

Question 5

Dietary cholesterol uptake?

Answer 5

500mg/day

Question 6

Where is cholesterol synthesised?

Answer 6

Bc of its need in cell membrane, all physiological requirements are supplied by LIVER
(de novo synthesis fro, acetyl-coA)

Question 7

What are the 3 main parts of cholesterol synthesis ?

Answer 7

1. Synthesis of isopentyl pyrophosphate (activated isoprene unit) = key building block. (Cytoplasm)
2. Condensation of 6 molecules of isopentenyl pyrophosphate to form squalene (cytoplasmic reac)
3. Cyclisation and demethylation of squalene by monooxygenases ro give cholesterol (ER)

Question 8

What is step 1 in synthesis of isopentenyl pyrophosphate?

Answer 8

2 molecules of acetyl coA condense to form the 4 carbon species Acetoacyl CoA

(break that thioester bond in one mol)

Question 9

What enzyme catalysts the formation of Acetoacetyl CoA?

Answer 9

Beta ketothiolase

CoA is excess product formed