Theme XV: Proteins

Definition and characteristics of proteins. Functions. Presence in nature. Methods of extraction and isolation.

Proteins are one of the primary compounds in the formation of life and are present in all organisms of the animal and plant kingdom.

These compounds play important roles in cell function and the processes of tissue formation.

In contrast to fats and carbohydrates, which also have a decisive role in vital functions as the main sources of energy, proteins vary in composition both between species and within the same body in different tissues and various cellular fluids.

For example, such as albumin composition varies depending on its obtaining source and the human proteins have different characteristics depending of the tissue: epithelial, muscle, brain, kidneys, etc.

These differences in composition also established physical and chemical differences in all life processes in which proteins are involved.

Proteins in nature

Proteins are present in all living matter, although with significant variation in their distribution.

In plants, which functional structures are essentially simple and complex carbohydrates, the protein present in the seed is significantly higher than elsewhere in the plant, since it is the responsible of retaining the genetic code for the reproduction of the specie.

This remarkable difference is not presented in the same way in animals, however there are variations in the composition of the different tissues.

Extraction and isolation of proteins

Proteins can be isolated by various methods:

• precipitation with solvent changes

• specific enzymatic reactions

• extraction by dialysis processes

• precipitation with saline solutions

• by lyophilization techniques

The first extractions are generally mixtures, which are subjected to complex purification methods including chromatographic techniques using ion exchange resins and cellulose derivatives.

see also

Proteins structure

Classification of proteins

Amino acids in proteins

Carbohydrates

Fixed oils and fats

Seed

Definition of Lipids. Classification according to chemical structure. Fixed oils and fats, waxes, sterols, phospholipids and glycolipids.