Q.Explain the composition of triglyceride.

A triglyceride is a simple lipid built from two kinds of component:

• Glycerol — a small molecule which is trihydroxy propane (a three-carbon backbone carrying three hydroxyl groups).
• Three fatty acids — each a carboxyl group attached to an R group, which may be a methyl group, an ethyl group, or a longer chain of CH2 groups. …

Among the lipids, the simplest are fatty acids, and one of the simplest ways they are put to use is by combining with glycerol. A triglyceride is exactly such a combination, and its composition has two parts.

The glycerol. Glycerol is a small molecule, chemically trihydroxy propane — a three-carbon chain that carries three hydroxyl groups. These three hydroxyl positions are the sites where fatty acids can be attached.

The three fatty acids. A fatty acid is a carboxyl group attached to an R group. That R group can be a methyl group (CH3), an ethyl group (C2H5), or a longer chain of CH2 groups running up to about nineteen carbons. Fatty acids may be saturated, with no carbon-to-carbon double bonds, or unsaturated, with one or more such double bonds — for example, palmitic acid has sixteen carbons and arachidonic acid has twenty. …

Method: Breaking a Composite Molecule into Its Building Blocks and Linkage

Any "explain the composition of X" question about a compound molecule is best tackled in three separate steps: identify the building-block components, identify the chemistry that joins them, and identify what varies to produce related but distinct molecules in the same family.

For a triglyceride, the two components to name are glycerol (a small three-carbon molecule with three hydroxyl groups) and fatty acids (a carboxyl group attached to a hydrocarbon chain of varying length and saturation). The linking chemistry is esterification — each fatty acid's carboxyl group reacts with one of glycerol's three hydroxyl groups to form an ester bond, releasing water. Naming the reaction type (esterification) and the resulting bond (ester bond) together, rather than just saying "they join," is what separates a complete answer from a partial one. …