Homologous Series

Proteins

Proteins contain nitrogen in addition to carbon, hydrogen and oxygen. They are the main body-building substance necessary for building new cells and replacing old ones. They are also essential for the formation of enzymes and hormones. Meat (flesh), milk and eggs are rich in problems.

All proteins are macromolecules made of smaller units called amino acids. There are twenty-five types of amino acids. in each protein, some or all the amino acid are present in different numbers and order so that each protein is unique. Proteins have to be digested to amino acids before they can be absorbed into the bodies of animals. The breakdown of proteins takes place in steps shown bellow.

Proteins are large complex molecules, characterized by high nitrogen content. Proteins are characteristics for each form of life and for each tissue that composes an organism. The development of an egg into a complex differentiated animal involves the formation of an enormous number of proteins that are specific for each tissue and organ. Proteins are composed of 20 commonly occurring amino acids. Nearly all of the 20 amino acid are usually present in every protein. Since the amino acids can be, and are arranged in all possible combination, it is easy to see how an almost infinite variety of protein can be produced.

Proteins are made up of poly-peptide chains. Some proteins, like myoglobin, consist of only one poly-peptide chain. Others may consist of more than one like or unlike poly-peptide chains. For example, hemoglobin is made up of four chains, two of one kind and two of another. The amino acid sequence in the poly-peptide chains of a protein is specified genes. This sequence is important since it determines the three dimensional structure of the protein and hence its biological function.

                               STRUCTURE AND SHAPE OF PROTEIN.

Proteins have well defined structures. The primary structure of a protein refers to the way in which the atoms of the protein molecules are joined to one another by covalent bonds to form chains and cross-linkages between chains.

AMINO ACIDS

AMINO ACIDS

Each of the 20 amino acids contain one amino group (-NH₂) and one carboxyl group (COOH) attached to the same carbon atom. The remainder of the molecule is unique for each amino acid. The general formula for amino acid is as follows:

The carbon atom of the amino acid to which the functional groups are attached is known as the α-carbon. In neutral solution, amino acids are mainly in the form of dipolar ions called Zwitterions.

There are twenty naturally occurring amino acids of biological importance. All proteins found in living organism are combinations of these amino acids. Some of these amino acids are known as essential amino acids because they cannot be synthesized in our body. Thus, these amino acids must be present in our dietary proteins. Some examples of amino acids are as follows: