The most abundant macromolecules found in the living cells are the proteins. They are present in all parts of the cell and in all the cells. There are various kinds of proteins, found in a single cell and these different proteins exhibit different biological functions. Proteins are the most important end products I most of the cycles and pathways. They can be considered as the molecular instruments through which genetic traits are expressed. The name protein is derived from the Greek word ‘protos’, which means ‘first’. americansciencelabs.com/melanotan-mt-2 talks about peptides and amino acids. You can find related information about amino acids, proteins and peptides at https://www2.chemistry.msu.edu/faculty/reusch/virttxtjml/proteins.htm
All proteins are made of ubiquitous set of 20 amino acids; from ancient bacteria to very complex life forms, all the proteins present are made of the 20 amino acids, linked through linear sequences. Their side chains determine the characteristic of the protein as even a slight change in the side chain could bring about changes in the chemical properties.
Amino acid chains form a protein and these amino acids are linked together by specific covalent bonds. By combining the 20 amino acids in different forms, a number of diverse proteins like antibodies, spider web, hormones, mushroom poison etc can be produced by cells.
Proteins can be broken down into amino acids by various methods. Asparagine was the first amino acid to be discovered in 1806. Threonine was the last amino acid among the 20 to be found, which wasn’t identified until1938. Amino acids were named after the sources from which they were first discovered. For example, asparagine was found in asparagus.
Structural features of amino acid
All the amino acids have a carboxyl group and an amino acid group is bound to the same carbon atom. Amino acids differ from each other by their side chains or R groups; these side chains vary in size, structure and they determine the electric charge and solubility of the amino acid in water. The amino acids that form the protein are referred to as primary, normal or standard amino acids to distinguish them from other amino acids that are modified after protein synthesis or from amino acids that are present in the body naturally but are not in any proteins.
The standard amino acids have been assigned one letter symbols and three letter abbreviations to indicate composition of sequence in amino acids. All standard amino acids except glycine have α carbon that is asymmetric and is bound to four substitute groups; an amino group, R group, carboxyl group and hydrogen atom. The α-carbon atom determines the chiral character of the amino acid. As the bonding orbital is found in a tetrahedral arrangement around the α-carbon, the four substituent groups could occupy two different arrangements which form non super imposable mirror images. The forms are called stereoisomer or enantiomer. The molecules with a chiral centre are called optically active as they can rotate plane polarized light.
The naming and classification of amino acids are based on the configuration of their four substituent groups. A reference compound will be chosen and all the optically active compared to this reference compound.