The amino acid is an organic acid in which one or more hydrogen atoms are replaced by NH2 group. It is one of the organic compounds, which represent the end product of the protein breakdown. All proteins are made up of amino acids. An amino acid contains a carbon atom, a free among group (containing nitrogen-NH2) and a carboxyl group (COOH). Amino acids are amphoteric in reaction and form salts with both acids and bases. The amino acids in the body are derivatives of saturated fatty acids. Amino acids are colourless, crystalline substance, soluble in water, easily diffusible and (except glycine) optically active. When the amino and carboxyl groups of amino acids combine acid residues. A peptide thus consists of 2 or more amino acid residues linked by peptide bonds. Read more about amino acid derivatives list
The metabolism of protein is meant by metabolism of amino acids. There is constant exchange of amino acid from tissue to blood and other body fluids and reversely from body flui to the tissue. The size of amino acid pool represents the balance between the removal and additions of amino acids are in two groups depending on the form in which amino acids are used.
I. Functions served by intact amino acid
- Synthesis of cell protoplasm. Amino acids are necessary to build up living cells, since proteins are main and essential constituents of them.
- Taking up wear and tear. Amino acids repair the damaged parts when tissue proteins break down during metabolism.
- Storage of protein. In adult/elderly people, protein breakdown exceeds protein synthesis; proteins cannot be stored when nitrogen equilibrium is established. But they can be stored in active/growing age, when protein synthesis exceeds protein breakdowns.
- Essential amino acids: There are some amino acids, which cannot be synthesized in the body, but are essential for growth and maintenance of life.
- Other synthesis process. Amino acids help in synthesis of bile acids, plasma proteins, haemoglobin, hormones, enzymes, milk proteins in lactating mothers, glutathione and cytochrome, purine and phyrimidine, melanin, antibodies, and formation of rhodypsin and urea. When the above functions are served by the amino acids in tact form, to the required stage, the surplus amounts of amino acids break down and undergo the following next group of functions.
II. Functions of Amino acids while breaking down
- Supply of energy. Amino acids liberate energy on break down at the rate of 4.3 Calories per gram of protein.
- Dynamic action. Amino Acids while breaking down, excret a specific stimulating action to the extent of about 30% on tissue metabolism.
- Deamination. During deamination under the influence of certain enzymes, the amino acid losses its radicle, into nitrogenous part and non-nitrogenous part, each of which perform separate function.
The nitrogenous part, ammonia, a large part (80%) of it is converted to Urea, and the smaller part combines with acids to form ammonium salts. It is also utilized for the synthesis of simple amino acids like glycine, alanine, glutamic acid; and some nitrogenous substances like creation, purine, uric acid, pyrimidine, lecithin etc.
The non-nitrogenous residues are utilized as carbohydrates, and some also get broken down as fatty acids in the body. It suphur and phosphorus components get converted into their compounds before excretion.