While there is free rotation around a single bond rotation, around a peptide bond is constrained. Although drawn as a single bond, the peptide bond behaves more like double bond. The peptide bond has a number of characteristics that are critical in determining how polypeptides behave. This generates an unbranched, linear polymer. When a polypeptide chain is being synthesized, new amino acid subunits are attached to the C- or carboxy terminus of the existing chain. Two molecules become one and water is released. The formation of a peptide bond involves a condensation / dehydration reaction. This is a complex polymer, composed of 20 different possible monomers that can, in theory, be linked together in any imaginable order. Two amino acids, joined together by a peptide bond, are known as a dipeptide.Īn amino acid polymer is known as a polypeptide. The bond between two amino acids is known as a peptide bond. Polymers are chains of subunits, monomers, linked together by chemical bonds. The different R-groups provide proteins with a range of chemical properties. Some of these R-groups are highly hydrophobic, some are hydrophilic, some are positively or negatively charged. These amino acids differ in their R-groups. They are found in biomolecules, such as the antibiotic gramicidin, which is composed of alternating L-and D-type amino acids.Įven though there are hundreds of different amino acids known, only 19 amino acids and one imino acid, proline, are found in proteins. O nly L-type amino acids are found in proteins, even though there is no theoretical reason that proteins cannot be made of both types of amino acids.ĭ-type amino acids do occur in nature. These enantiomers are mirror images of one another and are termed the L- and D- forms. If the four groups are different from one another, as they are in all amino acids except glycine, there are two possible stereoisomers, which are known as enantiomers. The four groups attached to the -carbon are arranged at the vertices of a tetrahedron. Proteins are composed of -amino acids linked together by peptide bonds into polypeptide chains.Īn amino acid is characterized by an amino group ( -NH 2) and a carboxylic acid group ( -COOH) linked to a carbon, known as the -carbon.Īlso attached to the -carbon is a H and various ' R-groups' or ' side-chains'. They can be motors, responsible for movements within cells, the movement of cells, tissues and the organism as a whole. They can be structural components, determining both the shape and mechanical properties of cells and tissues. They control the expression of genes, how genes respond to internal and external signals, and the replication of the genetic material. Proteins can act as catalysts and regulators of chemical reactions. The name acknowledges the many different functions and properties of proteins. Proteins derive their name from the ancient, but minor, Greek sea-god Proteus who, like your typical sea-god, could change shape. We have already mentioned proteins, since there is almost no biological process that does not rely on them.
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