Cholesterol

Question 1

Cholesterol biosynthesis - three main steps

Answer 1

1. Synthesis of isopentenyl pyrophosphate (cytoplasm)
2. Condense 6 molecule of isopentenyl pyrophosphate-> squalene. (Cytoplasm)
3. Cyclisation and demethylation of squalene by monooxygenase-> cholesterol (ER)

Question 2

Synthesis of isopentenyl pyrophosphate pt1

Answer 2

3 acetyl CoA->
3-hydroxy-3-methylglutaryl CoA
(HMG-CoA)
By HMG-CoA synthase

Question 3

Synthesis of isopentenyl pyrophosphate pt2

Answer 3

HMG-CoA -> mevalonate.
By HMG-CoA reductase

Question 4

Synthesis of isopentenyl pyrophosphate pt3

Answer 4

Mevalonate undergoes phosphorylation/decarboxylation -> 3-isopentenyl pyrophosphate

Question 5

Condensation of IPP to form squalene pt1

Answer 5

Isomerisation/group transfer.
Third IPP added to form-> farnesyl-pyrophosphate.

Question 6

Condensation of IPP to form squalene pt2

Answer 6

Farnesyl pyrophosphate (x2) -> squalene.

Condensation via squalene synthetase

Question 7

cyclisation and demethylation

Answer 7

squalene -(squalene monooxygenase)->cholesterol

Question 8

What is generated from cholesterol

Answer 8

Pregnenolone by desmolase

Question 9

What are the 5 classes of steroid hormone from pregnenolone

Answer 9

Progestagens
Glucocorticoid
Mineralcorticoid
Androgen
Estrogen

Question 10

What/where are bile salts made from

Answer 10

Cholesterol
In liver

Question 11

What lipoprotein do

Answer 11

Transport hydrophobic molecules in aq environment.

Phospholipid monolayer containing cholesterol and apoproteins.
This surrounds a core of cholesterol esters and triacylglycerols.

Question 12

How cholesterol esters are made

Answer 12

In plasma
Cholesterol+acyl chain. By LCAT