Lipids and Fats

Lipid:

Lipid molecules are all hydrophobic since they contain fewer polar O-H bonds and more nonpolar C-H bonds. Lipids are used for storing energy and building membranes.

Fats:

Fats are formed by excess carbohydrate and store energy in both animals and plants. The most common fat is called triacylglycerol or triglyceride, which combined with a glycerol molecule and three fatty acids.

*Glycerol – three carbon alcohol.

*Fatty acid – long hydrocarbon chain containing a single carboxyl group.

Fatty acid can be either saturated or unsaturated. Saturated fatty acids only contain single bonds and make these fatty acids fit more closely together. (Like lard and butter.) Unsaturated fatty acids contain double bonds between carbon atoms, and make the fats in a form of liquid. (Like olive oil and sunflower oil.)

When a glycerol molecule reacts with three fatty acids, three –H atoms from the hydroxyl groups combined with three –OH from the carboxyl groups, and form three water molecules. The bonds between a glycerol and fatty acids are called ester bonds.

Phospholipids:

Phospholipids are made of one glycerol molecule, two fatty acids and a polar phosphate group. Since the phospholipids have both polar and nonpolar parts, they can form a bilayer and act as the main components in cell membrane. The hydrophilic head (polar phosphate group) can mix with water whereas the hydrophobic tails (nonpolar fatty acids) only can mix with each other in the center of bilayer.

Sterols:

Sterols contain four fused hydrocarbon rings and few different functional groups. Cholesterol is an important steroid component of cell membranes. Cholesterol is often converted into vitamin D and bile salts.

Waxes:

Waxes are another lipid containing long-chain fatty acids attached to alcohols or carbon rings.

Waxes are usually used to form waterproof coatings

on plants or animals.