Structure and Function of Lipids in Plants and Animals

Structure and Function of Lipids in Plants and Animals

Lipids are the name given to a mixed group of organic compounds. The

elements Hydrogen, Oxygen and Carbon are always found in Lipids. The

difference between them and Carbohydrates is that they have a lower

proportion of Oxygen in the molecule. Lipids are insoluble in water,

but they are soluble in organic solvents, such as ether, acetone,

chloroform or benzene.

There are several parts in the group of Lipids:

o fats and oils,

o waxes,

o phospholipids,

o steroids (like cholesterol, oestrogen and testosterone), and some

other related compounds.

At room temperature, fats are solids and oils are liquids. Fats and

oils are typically found in animals and plants. Fats are of animal

origin, while oils tend to be found in plants. Fats and oils are made

up of a glycerol (a type of alcohol with a hydroxyl group on each of

its three carbons) and three fatty acids (an organic acid). Since

there are three fatty acids attached, these are known as triglycerides.

A condensation reaction produces a triglyceride and water molecule

when the glycerol and three fatty acids react together (see diagram

below). The fatty acid molecules are insoluble in water because of

their long hydrocarbon tails (the tails are referred to as hydrophobic

or “water-hating”). The head of the molecule is a carboxyl group which

is hydrophilic or “water-loving”.

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Fatty acids are the main component of soap, where their tails are

soluble in oily dirt and their heads are soluble in water to emulsify

and wash away the oily dirt. However, when the head end is attached to

glycerol to form a fat, that whole molecule is hydrophobic.

The digestion of triglycerides is catalysed by lipase enzymes which

are found, for example, in the digestive system of animals and in

germinating seeds, in the lysosomes inside cells and in the secretions

of saprophytic bacteria and fungi. Triglycerides are created in fat

storage depots, in such places as, in liver cells, in the adipose