Explain the structure and functions of cholesterol.

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Hint: The molecular formula of cholesterol is \[{{C}_{27}}{{H}_{46}}O\]. Cholesterol contains 4 rings in its structure, one double bond, one hydroxyl group and one hydrocarbon chain. Cholesterol is also known as a "sterol" because it contains alcohol and a steroid moiety in its structure.

Complete answer:
Structure of cholesterol:
We know that Cholesterol is a lipid having a structure consisting of four hydrocarbon rings forming the bulky steroid structure and they are labeled with numbers 1, 2, 3 and 4. We can see the numbering in the below structure.
There is a hydrocarbon chain containing eight carbon atoms linked to five membered rings of the steroid.
There is a double bond in the ring-2 of the cholesterol.
Cholesterol contains a hydroxyl group linked to the first six membered rings in the structure.
The hydroxyl group of cholesterol is capable of forming hydrogen bonds with the nearby oxygen of the carbonyl group of phospholipid.

Functions of cholesterol:
Cholesterol is a vital constituent of the cell membrane.
Cholesterol is going to maintain proper membrane permeability and fluidity of the cells.
Cholesterol is going to involve the synthesis of Steroid Hormones, Vitamin-D and Bile Acids in the cells.

Note: Cholesterol is not present in prokaryotes like bacteria and archaea. Because prokaryotes do not contain a proper cell wall in their structure. By using sunlight cholesterol present in the skin of eukaryotes prepares vitamin-D which is useful to absorb calcium from the intestine.