Provide information regarding the structure of lipids.

(N/A) $\Rightarrow$ Lipids are generally water-insoluble. They could be simple fatty acids.
$\Rightarrow$ $A$ fatty acid has a carboxyl group attached to an $R$ group.
$\Rightarrow$ The $R$ group could be a methyl $(-CH_{3})$,or ethyl $(-C_{2}H_{5})$ or higher number of $-CH_{2}$ groups ($1$ carbon to $19$ carbons). For example,palmitic acid has $16$ carbons including the carboxyl carbon. Arachidonic acid has $20$ carbon atoms including the carboxyl carbon.
$\Rightarrow$ Fatty acids could be saturated (without double bond) or unsaturated (with one or more $C=C$ double bonds).
$\Rightarrow$ Another simple lipid is glycerol,which is trihydroxy propane.
$\Rightarrow$ Many lipids have both glycerol and fatty acids. Here,the fatty acids are esterified with glycerol. They can be monoglycerides,diglycerides,and triglycerides. These are also called fats and oils based on their melting point.
$\Rightarrow$ Oils have a lower melting point (e.g.,gingelly oil) and hence remain as oil in winters.
$\Rightarrow$ Some lipids have phosphorus and a phosphorylated organic compound in them. These are phospholipids. They are found in the cell membrane. Lecithin is one example. Some tissues,especially neural tissues,have lipids with more complex structures.