File Name: protein and amino acid requirements in human nutrition .zip
Protein is an important part of every diet. The amount of protein an individual needs depends on their age and sex. Protein is a part of every cell in the body. It helps the body to build and repair cells and tissues. Protein is a major component of the skin, muscle, bone, organs, hair, and nails.
An essential amino acid , or indispensable amino acid , is an amino acid that cannot be synthesized from scratch by the organism fast enough to supply its demand, and must therefore come from the diet. Of the 21 amino acids common to all life forms, the nine amino acids humans cannot synthesize are phenylalanine , valine , threonine , tryptophan , methionine , leucine , isoleucine , lysine , and histidine. Six other amino acids are considered conditionally essential in the human diet, meaning their synthesis can be limited under special pathophysiological conditions, such as prematurity in the infant or individuals in severe catabolic distress. Six amino acids are non-essential dispensable in humans, meaning they can be synthesized in sufficient quantities in the body. These six are alanine , aspartic acid , asparagine , glutamic acid , serine ,  and selenocysteine considered the 21st amino acid. Pyrrolysine , which is proteinogenic only in certain microorganisms, is not used by and therefore non-essential for most organisms, including humans.
NCBI Bookshelf. Recommended Dietary Allowances: 10th Edition. Both animal and plant proteins are made up of about 20 common amino acids. The proportion of these amino acids varies as a characteristic of a given protein, but all food proteins—with the exception of gelatin—contain some of each. Amino acids are required for the synthesis of body protein and other important nitrogen-containing compounds, such as creatine, peptide hormones, and some neurotransmitters. Although allowances are expressed as protein, a the biological requirement is for amino acids.
E-mail: g-wu tamu. A protein consists of amino acids AA linked by peptide bonds. Dietary protein is hydrolyzed by proteases and peptidases to generate AA, dipeptides, and tripeptides in the lumen of the gastrointestinal tract. These digestion products are utilized by bacteria in the small intestine or absorbed into enterocytes. AA that are not degraded by the small intestine enter the portal vein for protein synthesis in skeletal muscle and other tissues. AA are also used for cell-specific production of low-molecular-weight metabolites with enormous physiological importance.
Few issues in nutritional science have aroused such long-standing and deep-seated controversies as protein and amino acid requirements. Lusk wrote that both opinions were proper themes for psychoanalysis. Students of the history of science looking at the current debate about amino acid requirements might have the same response today. It is appropriate to consider these issues here, given the most recent article published in The Journal of Nutrition in support of the MIT amino acid scoring pattern McLarney et al.
Proteins , like carbohydrates and fats, contain carbon , hydrogen , and oxygen , but they also contain nitrogen , a component of the amino chemical group NH 2 , and in some cases sulfur. Proteins serve as the basic structural material of the body as well as being biochemical catalysts and regulators of genes. Aside from water , protein constitutes the major part of muscles, bones, internal organs, and the skin , nails , and hair. Protein is also an important part of cell membranes and blood e. Enzymes , which catalyze chemical reactions in the body, are also protein, as are antibodies , collagen in connective tissue , and many hormones, such as insulin. Tissue proteins are in a dynamic equilibrium with proteins in the blood, with input from proteins in the diet and losses through urine , feces , and skin.
Protein is an essential nutrient for whole body particularly growth and development. Dietary protein can be derived from both plant and animal sources which may have differences in protein quality. High quality protein is very important for support health in early and later life.
Skip to search form Skip to main content You are currently offline. Some features of the site may not work correctly. Corpus ID: Protein and amino acid requirements in human nutrition. The World Health Organization and the Food and Agriculture Organization have worked to quantify the energy and nutrient needs of populations since View on PubMed.