Question

Describe various forms of lipid with a few examples.

Answer 1

Introduction to lipids

1. Lipids are organic compounds containing carbon, hydrogen and oxygen.
2. They are insoluble in water but are soluble in organic solvents.
3. They are of the following major types:

• Simple lipid: Triglyceride, wax etc.
• Compound lipids: Phospholipids, glycolipids etc.
• Derivatives like steroids etc.

Simple lipid

Fats can be monoglycerides, diglycerides, triglycerides.

• A fat molecule consisting of one molecule of glycerol (-OH end) attached to three molecules long chain fatty acids (-COOH end) are referred to as triglycerides.
• Oil is also a form of lipid similar to fats but it has double bonds in its fatty acid chain which makes it liquid at room temperature.
• Waxes are esters of fatty acids with long chain alcohol of high molecular weight instead of glycerol. Example: Beeswax

Compound lipids

• Phospholipids are amphipathic molecules composed of two molecules of fatty acids linked to the glycerol unit and the third OH of glycerol linked to a phosphate group which is esterified to an organic molecule. Example: Phosphatidylserine, Phosphatidylcholine, Phosphatidylethanolamine etc.
• Glycolipids are those lipids having a carbohydrate attached to the lipid by a glycosidic (covalent) bond. Example: Glycosphingolipid

Derivatives like steroids

• Steroids are lipids composed of four fused carbon rings (usually (three six-membered and one five-membered) called a sterol ring instead of a straight fatty acid chain.
• Example: Cholesterol

Prostoglandins

• They are derivatives of arachidonic acid and contain 20 C-atoms. These are biologically active lipids.