Protein Metabolism
Dietary proteins are broken down into amino acids in the stomach & intestines: 1/3 is absorbed into the blood stream in the form of amino acids and 2/3 in the form of small peptides (peptide bonded amino acids).
About 1/4 of the amino acids released during protein breakdown are fully degraded. Thus, 3/4 are transported to various locations in the body where they are re-synthesized into the proteins required for muscle & connective tissue development, and enzyme & hormone formation, etc.
The majority of the body’s amino acid supply comes from breakdown (catabolism) of its own cells: 125-250g of body protein is broken down and re-synthesized each day. The average adult needs to consume 30-60g of protein/day to replace those amino acids that are normally metabolized.
Protein turnover is rapid (3-4 days) in some tissues, such as the liver and intestines, but slower (few months) for muscular proteins, bones and connective tissue.
Athletes require more proteins to compensate for more muscle protein synthesis, needed for the repair of any muscle damage from prolonged exercise.
Animals use nitrogen-containing amino acids from plant sources, as basic building blocks for the manufacture of proteins and nucleic acids.
Plant-feeding insects are dependent on nitrogen in their diet. The amount of nitrogen fertilizer applied to a plant can affect the reproduction rate of insects feeding on it.
