Proteins play a vital role in the nutrition of an organism. They are necessary for carrying out a number of essential body functions that have already been discussed in the earlier chapter.
The end product of protein break-down, amino acids, is absorbed by the blood. A regular supply of essential amino acids is the basic requirement for the well-being of an individual, while nonessential amino acids can be obtained from-
i. Dietary intake
ii. Synthesis form amino acids present in tissues
iii. Synthesis of amino acids from organic acids.
Amino acids are the building blocks for synthesis of cellular, sub-cellular and other organic substances. All amino acids are joined together in different sequences and in varying numbers thereby giving rise to several thousand proteins. Tissues vary in their chemical composition because of the presence of different amino acids. The brain is an organ that has a higher percentage of glutamine, glutamic acid and other non-essential amino acids than other tissues.
Essential substances like lipo-proteins, albumen, globulin and hemoglobin are synthesised from amino acids. Nucleo-protein is a conjugated protein and behaves as genes in the chromosomes. It is responsible for cell production and division and provides hereditary information.
Hormones and enzymes synthesised from amino acids regulate body functions and control the rate of biological reactions.
The tissues can hold only a small amount of free amino acids. Excess amino acids are de-aminised by the liver. The ammonia released is converted into urea and excreted as urine and the energy is utilized for the body activities. Some amino acids can be converted into glucose that may be utilised or stored. These are known as glucogenic amino acids that encourage gluconeogenesis. Those which can be converted to fatty acids are called ketogenic amino acids. These give rise to acetoacetic acid and other ketone bodies.
Deficiency or improper utilisation of amino acids leads to serious consequences like low resistance, low plasma protein level and insufficient hormonal secretions. During this period the body is in negative balance and draws upon ‘labile proteins’ (plasma proteins and liver proteins). When the losses of nitrogen equal the intake, the body is said to be in nitrogen equilibrium. Normal adults are in nitrogen balance. During childhood, convalascence and pregnancy the losses are less than the intake and the body is said to be in positive nitrogen balance.