General description of protein

Protein is one of the nutrients along with carbohydrate, fat, vitamins, minerals, and water.

Proteins are single, unbranched chains of amino acid monomers. Amino acids are the building blocks of proteins. There are 20 different naturally occurring amino acids. The amino acid side chains in a peptide can become modified, extending the functional repertoire of amino acids to more than hundred different amino acids. A protein’s amino acid sequence determines its three-dimensional structure.

To make a protein, these amino acids are joined together in a polypeptide chain through the formation of a peptide bond.

Chains that are less than 40-50 amino acids or residues are often referred to as polypeptide chains since they are too small to form a functional domain. Larger than this size, they are called proteins.

Humans can synthesize 12 (nutritionally nonessential) of the 20 common amino acids from the amphibolic intermediates of glycolysis and of the citric acid cycle. Of the 12 nutritionally nonessential amino acids, nine are formed from amphibolic intermediates and three (cysteine, tyrosine and hydroxylysine) from nutritionally essential amino acids. Protein is an essential nutrient. There is no life without protein.

Protein is contained in every part of human body, the skin, muscles, hair, blood, body organs, eyes, even fingernails and bone. Next to water, protein is the most plentiful substance in human body.

Protein has a critical physiological function. Protein is primarily used in the body to build, maintain, and repair body tissues. In the event that protein intake is greater than that required by the body for this primary function, excessive protein is converted to energy for immediate use or stored in the body as fat.
General description of protein

General structure of an amino acid