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Key People:James phường AllisonCarl SaganDorothy Maud WrinchCharles Yanofsky...(Show more)Related Topics:creatineglutamic acidtryptophanalanineglutamine...(Show more)
An amino acid is an organic molecule that is made up of a basic amino group (−NH2), an acidic carboxyl group (−COOH), and an organic R group (or side chain) that is chất lượng to each amino acid.
Nine of these amino acids are considered essential—they must be consumed in the diet—while five are considered nonessential in that they can be made by the human body. The remaining six protein-building amino acids are conditional, being essential only at certain life stages or in certain disease states.Some authorities recognize a 21st amino acid, selenocysteine, which is derived from serine during protein biosynthesis.
Amino acids typically are classified as standard or nonstandard, based on the polarity, or distribution of electric charge, of the R group (side chain).
In addition khổng lồ their role as protein building blocks in living organisms, amino acids are used industrially in numerous ways. The first report of the commercial production of an amino acid was in 1908. It was then that the flavouring agent monosodium glutamate (MSG) was prepared from a type of large seaweed. This led lớn the commercial production of MSG, which is now produced using a bacterial fermentation process with starch và molasses as carbon sources. Glycine, cysteine, & D,L-alanine are also used as food additives, and mixtures of amino acids serve as flavour enhancers in the food industry.
Amino acids are used therapeutically for nutritional and pharmaceutical purposes. For example, treatments with single amino acids are part of the medical approach lớn control certain disease states. Examples include L-dihydroxyphenylalanine (L-dopa) for Parkinson disease; glutamine & histidine to treat peptic ulcers; and arginine, citrulline, and ornithine to treat liver diseases.
Read more below: Some common uses
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amino acids
The structure & function of amino acids.
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amino acid, any of a group of organic molecules that consist of a basic amino group (―NH2), an acidic carboxyl group (―COOH), & an organic R group (or side chain) that is unique to each amino acid. The term amino acid is short for α-amino
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The amino acids differ from each other in the particular chemical structure of the R group.
Building blocks of proteins
Proteins are of primary importance khổng lồ the continuing functioning of life on Earth. Proteins catalyze the vast majority of chemical reactions that occur in the cell. They provide many of the structural elements of a cell, & they help to bind cells together into tissues. Some proteins act as contractile elements lớn make movement possible. Others are responsible for the transport of vital materials from the outside of the cell (“extracellular”) khổng lồ its inside (“intracellular”). Proteins, in the form of antibodies, protect animals from disease and, in the size of interferon, mount an intracellular attack against viruses that have eluded destruction by the antibodies and other immune system defenses. Many hormones are proteins. Last but certainly not least, proteins control the activity of genes (“gene expression”).
This plethora of vital tasks is reflected in the incredible spectrum of known proteins that vary markedly in their overall size, shape, và charge. By the end of the 19th century, scientists appreciated that, although there exist many different kinds of proteins in nature, all proteins upon their hydrolysis yield a class of simpler compounds, the building blocks of proteins, called amino acids. The simplest amino acid is called glycine, named for its sweet taste (glyco, “sugar”). It was one of the first amino acids khổng lồ be identified, having been isolated from the protein gelatin in 1820. In the mid-1950s scientists involved in elucidating the relationship between proteins & genes agreed that 20 amino acids (called standard or common amino acids) were khổng lồ be considered the essential building blocks of all proteins. The last of these lớn be discovered, threonine, had been identified in 1935.
Chirality
All the amino acids but glycine are chiral molecules. That is, they exist in two optically active asymmetric forms (called enantiomers) that are the mirror images of each other. (This property is conceptually similar to the spatial relationship of the left hand khổng lồ the right hand.) One enantiomer is designated d và the other l. It is important to note that the amino acids found in proteins almost always possess only the l-configuration. This reflects the fact that the enzymes responsible for protein synthesis have evolved to lớn utilize only the l-enantiomers. Reflecting this near universality, the prefix l is usually omitted. Some d-amino acids are found in microorganisms, particularly in the cell walls of bacteria & in several of the antibiotics. However, these are not synthesized in the ribosome.
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Acid-base properties
Another important feature of không lấy phí amino acids is the existence of both a basic & an acidic group at the α-carbon. Compounds such as amino acids that can act as either an acid or a base are called amphoteric. The basic amino group typically has a pKa between 9 and 10, while the acidic α-carboxyl group has a pKa that is usually close to 2 (a very low value for carboxyls). The pKa of a group is the pH value at which the concentration of the protonated group equals that of the unprotonated group. Thus, at physiological pH (about 7–7.4), the miễn phí amino acids exist largely as dipolar ions or “zwitterions” (German for “hybrid ions”; a zwitterion carries an equal number of positively và negatively charged groups). Any không tính tiền amino acid and likewise any protein will, at some specific pH, exist in the khung of a zwitterion. That is, all amino acids and all proteins, when subjected lớn changes in pH, pass through a state at which there is an equal number of positive & negative charges on the molecule. The pH at which this occurs is known as the isoelectric point (or isoelectric pH) and is denoted as pI. When dissolved in water, all amino acids & all proteins are present predominantly in their isoelectric form. Stated another way, there is a pH (the isoelectric point) at which the molecule has a net zero charge (equal number of positive and negative charges), but there is no pH at which the molecule has an absolute zero charge (complete absence of positive and negative charges). That is, amino acids & proteins are always in the form of ions; they always carry charged groups. This fact is vitally important in considering further the biochemistry of amino acids và proteins.