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Protein sequence is typically notated as a string of letters, listing the amino acids starting at the amino-terminal end through to the carboxyl-terminal end. Either a three letter code or single letter code can be used to represent the 22 naturally encoded amino acids, as well as mixtures or ambiguous amino acids (similar to nucleic acid ...
Proteins form by amino acids undergoing condensation reactions, in which the amino acids lose one water molecule per reaction in order to attach to one another with a peptide bond. By convention, a chain under 30 amino acids is often identified as a peptide, rather than a protein. [1]
The common natural forms of amino acids have a zwitterionic structure, with −NH + 3 (−NH + 2 − in the case of proline) and −CO − 2 functional groups attached to the same C atom, and are thus α-amino acids, and are the only ones found in proteins during translation in the ribosome.
The side chains of the standard amino acids have a variety of chemical structures and properties, and it is the combined effect of all amino acids that determines its three-dimensional structure and chemical reactivity. [35] The amino acids in a polypeptide chain are linked by peptide bonds between amino and carboxyl
At the top level are all alpha proteins (domains consisting of alpha helices), all beta proteins (domains consisting of beta sheets), and mixed alpha helix/beta sheet proteins. While most proteins adopt a single stable fold, a few proteins can rapidly interconvert between one or more folds. These are referred to as metamorphic proteins. [5]
Peptides and proteins are often described by the number of amino acids in their chain, e.g. a protein with 158 amino acids may be described as a "158 amino-acid-long protein". Peptides of specific shorter lengths are named using IUPAC numerical multiplier prefixes:
Ribbon diagram of a protease (TEV protease) complexed with its peptide substrate in black with catalytic residues in red.(. A protease (also called a peptidase, proteinase, or proteolytic enzyme) [1] is an enzyme that catalyzes proteolysis, breaking down proteins into smaller polypeptides or single amino acids, and spurring the formation of new protein products. [2]
The amino acids that make up a particular helix can be plotted on a helical wheel, a representation that illustrates the orientations of the constituent amino acids (see the article for leucine zipper for such a diagram). Often in globular proteins, as well as in specialized structures such as coiled-coils and leucine zippers, an α-helix will ...