Cholesterol - Cholesterol Biosynthesis

Question 1

What is cholesterol?

Answer 1

Steroid

Increases or decreases membrane stiffness depending on temp and nature of membrane

Question 2

Step 1: synthesis of isopentenyl pyrophosphate

Answer 2

Condensation of 2 acetyl-CoA molecules to form ace to acetyl CoA

Condensation of another acetyl-CoA molecule to from HMG-CoA

HMG-CoA reduced to generate mevalonate

Mevalonate undergoes sequential phosphorylation and Decarboxylation to form 3-isopentenyl pyrophosphate

Question 3

Step 2: condensation IPP to form squalene

Answer 3

Isomerization reaction to produce dimethylallyl pyrophosphate

Condenses with unit of isopentenyl-PP to form Geranyl-PP (10C)

Third isopentenbyl-PP molecule added to from farnesyl-PP (15C)

2 farnesyl-PP molecules condense to form squalene (30C) and 2x pyrophosphate

Question 4

Step 3: cyclisation and demethylation

Answer 4

Further 19 steps to from cholesterol

Question 5

Cholesterol and steroids

Answer 5

Basis of steroid hormones

Precursor pregnenolone generated from cholesterol by action of desmolase enzyme

Question 6

Synthesis of vitamin D from cholesterol

Answer 6

Sunlight is required to initiate the reaction scheme

Calcitriol plays a key role in calcium metabolism

Question 7

Bile slats are synthesised from cholesterol

Answer 7

Cholesterol converted by a series of reactions to form the primary bile salt glycocholate and taurocholate