Lipids

Lipids comprise a rather heterogeneous class of compounds which are sparingly soluble in water, but show considerable solubility in organic solvents like ether, cholorform, benzene, hot alcohol and petroleum ether. These physical properties indicate the hydrophobic nature of the hydrocarbon structure, although lipids may also contain some hydrophilic groups.

Lipids have several biological functions.

(1) Certain lipids, e.g. triglycerides, are storage compounds for the reserve energy of the body, e.g. lipids of the fat body and subcutaneous fat.

(2) Lipids are important components of cell membranes. The plasma membrane of eukaryote cells is composed primarily of lipids and proteins, along with carbohydrates in some cases.

(3) In nerve fibers the myelin sheath contains lipids which act as electrical insulators.

(4) As components of subcutaneous tissue lipids are important for insulation of heat.

(5) Some hormones, e.g. steroids, are lipids.

(6) Some lipids are important as vitamins.

(7) Lipids also occur as components of some enzyme systems.