Lecture Notes

Cholesterol and steroids
Learning objectives:

1. Describe in general the 3 stage process of cholesterol synthesis from acetyl CoA.
2. Describe the regulation of cholestrol synthesis
3. Describe the transport of choletrol and TAGs around the body
4. Role of cholestery esters
5. Describe the structure of lipoprotein particles

Why is cholesterol vital?

 Cholesterol has a crucial role in:
- Structure of membranes
- Precursor of steroid hormones
e.g. progesterone
testosterone
estrogen
- precursor bile acid & vitamin D
- its biosynthesis exemplifies a fundamental mechanism for
assembly of extended C skeleton from 5-C units
- regulation of cholesterol synthesis and transport great example
of how biochemistry feeds into medicine




Sources of cholesterol

 cholesterol is an essential molecule but not required in diet because all cells can synthesis
cholesterol from simple precursors.

, De novo cholesterol synthesis

 similar to ketogenic pathway (ketne bodies)
 occurs in cytosol
 requires NADPH and ATP
 highly regulated
 80 % in lives (~1g/d)
 10 % in intestine
 ~5 % in skin
 All of its carbon atoms are provided by a single precursor
- Acetate (as acetyl-CoA)