Biology · Biomolecules · NEET
NCERT says lipids are generally water insoluble and can be simple fatty acids, or they may contain both glycerol and fatty acids together. So the two basic building blocks you must remember for NEET are fatty acids and glycerol. When fatty acids join glycerol, you get mono-, di-, or triglycerides (fats and oils).
A fatty acid has a carboxyl group (–COOH) attached to an R group. The R group can be a methyl (–CH3), an ethyl (–C2H5), or a longer chain of –CH2 groups (1 carbon up to 19 carbons). Example: palmitic acid has 16 carbons including the carboxyl carbon, and arachidonic acid has 20 carbons including the carboxyl carbon. NEET often asks these carbon counts directly.
Yes, NCERT lists glycerol as another simple lipid. It is called trihydroxy propane because it is a 3-carbon (propane) molecule carrying three hydroxyl (–OH) groups. Those three –OH sites are the reason one glycerol can bind up to three fatty acids.
One glycerol combines with up to three fatty acids because glycerol has only three –OH groups. A typical fat (triglyceride) is one glycerol plus three fatty acids. One fatty acid gives a monoglyceride, two give a diglyceride, and three give a triglyceride. This exact ratio was tested in NEET 2016.
The fatty acid is joined to glycerol by an ester bond (this is called esterification). The –COOH of the fatty acid reacts with an –OH of glycerol to form the ester linkage. That is why lipids like triglycerides are called esters and are not true polymers.
No. A fatty acid is a long carbon chain ending in a carboxyl group (–COOH). Glycerol is a small 3-carbon molecule with three –OH groups (trihydroxy propane). They are two different simple lipids that join together by ester bonds to form fats and oils.
A typical fat molecule is made up of:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
The R group is the carbon chain attached to the carboxyl group. NCERT says it can be a methyl (–CH3), ethyl (–C2H5), or a longer run of –CH2 groups, from 1 carbon up to 19 carbons.
Palmitic acid has 16 carbons including the carboxyl carbon. This is a common NEET fact, often paired with arachidonic acid (20 carbons including the carboxyl carbon).
Because it is a 3-carbon (propane) backbone carrying three hydroxyl (–OH) groups. These three –OH sites let it bind up to three fatty acids.
No. NCERT states lipids are generally water insoluble but are soluble in organic solvents. This water-insoluble nature is a frequently tested NEET point.
No. A triglyceride is an ester of three fatty acids with glycerol, not a chain of repeating monomer units, so lipids are not true polymers even though they can be large.
