This is an old revision of this page, as edited by 209.234.79.205 (talk) at 02:34, 7 July 2002. The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.
Revision as of 02:34, 7 July 2002 by 209.234.79.205 (talk)(diff) ← Previous revision | Latest revision (diff) | Newer revision → (diff)Proteins (originally meaning first thing when discovered in 1838 by Berzelius) are one of the basic classes of substances studied in biochemistry.
Proteins are biopolymers consisting of one or more strings of amino acid residues joined head-to-tail via peptide bonds. Each string folds into a 3-dimensional structures. The two most regular structural motifs in proteins are alpha helices and beta sheets, which are stabilized by hydrogen bonds between the C=O and N-H groups of different peptide bonds. The string is folded further into larger 3-dimensional structures that are held together by hydrogen bonds, hydrophobic interactions, and/or disulfide bonds, etc. Many proteins consist of two or more subunits, which are each a continuous string of amino acids.
Proteins are generally large molecules, sometimes having molecular masses of up to 100,000. Such long chains of amino acids are almost universally referred to as proteins, but shorter strings of amino acids are referred to as "polypeptides" and "oligopeptides". The dividing line is somewhat undefined, although a polypeptide may be less likely to have tertiary structure and may be more likely to act as a hormone (like insulin) rather than as an enzyme or structural element.
Nearly all the biological catalysts known as enzymes are proteins. (Some RNA was shown in the late 20th century to have catalytic properties as well.) Immunoglobulins, membrane-bound receptors, and trans-membrane transporters are also proteins. Finally, protein also makes up much of the structure of animals: collagen and keratin are components of skin, hair, and cartilage; and muscles are composed largely of proteins.
During the 1980s scientists started developing a technology known as protein engineering which can alter the structure of a protein and hence its properties. (Genetic engineering is another technique, which modifies a protein at an earlier stage of its production in vivo, by modifying the gene that codes for it.)
Protein deficiency is often discussed in relation to starvation and malnourishment in Third World Countries. It may be an overlooked health factor even in developed countries such as the United States, where diets may rely heavily on carbohydrates and there is societal pressure to be thin. Protein deficiency can lead to sympotoms such as fatigue, insulin resistance, hair loss, loss of hair pigment (hair that should be black becomes reddish), loss of muscle mass, low body temperature, and hormonal irregularities. Severe protein deficiency is fatal.
Excess protein can cause problems as well, such as foundering (foot problems) in horses.
See also: