Since the liver takes up cholesterol in the form of LDL, why does it need to make cholesterol from acetyl CA?

Question

since it already uses the LDL receptor to endocytose LDL, and break LDL to get cholesterol... why would it need to use HMG COA reductase to *make* cholesterol??

Answer 1

Everyday after you eat you lose some bile salts which will not be re-absorbed. Bile salts contain cholesterol and so basically everyday you are losing some cholesterol. You are also making hormones which "use up" some of your cholesterol.

Food supplies some cholesterol via lipoproteins (as you said) but when that is not sufficient you NEED to get it from somewhere, so the body synthesises it. (What would happen if you were starving???)

Also when the cells endocytose the cholesterol regulatory actions occur. This causes inhibition of HMG COA reductase activity, decreases LDL recptors and increases esterification of the cholesterol.