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Proteins are the molecular workhorses of all known biological systems. Among other functions, they are the motors that cause muscle contraction, the catalysts that drive life-sustaining chemical processes, and the molecules that hold cells together to form tissues and organs.
The following is a list of a few of the diverse biological processes mediated by proteins:
The estimate of the number of genes in the human genome has been changing dramatically since it was annotated (the latest gene count estimates can be found in this Wikipedia article on the human genome ). Each gene encodes one or more distinct proteins. The total number of distinct proteins in the human body is larger than the number of genes due to alternate splicing . Of those, only a small fraction have been isolated and studied to the point that their purpose and mechanism of activity is well understood. If the functions and relationships between every protein were fully understood, we would most likely have a much better understanding of how our bodies work and what goes wrong in diseases such as cancer, amyotrophic lateral sclerosis, Parkinson's, heart disease and many others. As a result, protein science is a very active field. As the field has progressed, computer-aided modeling and simulation of proteins have found their place among the methods available to researchers.
An amino acid is a simple organic molecule consisting of a basic (hydrogen-accepting), amine group bound to an acidic (hydrogen-donating) carboxyl group via a single intermediate carbon atom: During the translation of a gene into a protein, the protein is formed by the sequential joining of amino acids end-to-end to form a long chain-like molecule, or polymer . A polymer of amino acids is often referred to as a polypeptide . The genome is capable of coding for 20 different amino acids whose chemical properties depend on the composition of their side chains ("R" in the above figure). Thus, to a first approximation, a protein is nothing more than a sequence of these amino acids (or, more properly, amino acid residues , because both the amine and acid groups lose their acid/base properties when they are part of a polypeptide). This sequence is called the primary structure of the protein. The Wikipedia entry on amino acids provides a more detailed background, including the structure, properties, abbreviations, and genetic codes for each of the 20 common amino acids.
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