Protein Turnover

 Protein Turnover

Protein turnover refers to the replacement of older proteins as they are broken down within the cell. Different types of proteins have very different turnover rates.

A balance between protein synthesis and protein degradation is required for good health and normal protein metabolism. More synthesis than breakdown indicates an anabolic state that builds lean tissues, more breakdown than synthesis indicates a catabolic state that burns lean tissues. According to D.S. Dunlop, protein turnover occurs in brain cells the same as any other eukaryotic cells. Protein turnover is believed to decrease with age in all senescent organisms including humans. This results in an increase in the amount of damaged protein within the body. Four weeks of aerobic exercise has been shown to increase skeletal muscle protein turnover in previously unfit individuals. A diet high in protein increases whole body turnover in endurance athletes.

Synthesis of proteins in the body- Human body can synthesize protein molecules from the amino acids absorbed from the intestine by the process of DNA Replication, Transcription and Translation through RNA molecules in the cells. Human body can synthesize certain amino acids, such as glycine, alanine, glutamic acid etc.

The body cannot synthesize certain amino acids known as essential amino acids. Experimentally it has been shown that amino acids can be synthesized by perfusing isolated liver tissue with ammonia and corresponding ketonic or hydroxy acids. These acids may come from the non-nitrogenous part of amino acids as well as from the breakdown products of carbohydrates and fats. The amino acids, keto acids and hydroxy acids are interconvertible in the body, the intermediate link being a keto acid,