Structure, classification and
nomenclature of amino acids
Amino acid refers to any compound containing an amino
group and a carboxyl group. Amino acids are the basic
structural units of proteins. They contain an amino
group and a carboxyl group. Chiral carbon has four
different types of atoms or groups attached to it. Most
proteins are formed of 20 amino acids. Glycine is the
simplest amino acid. Usually, amino acids are coded with
three letters. Ex: Alanine is coded as Ala. Amino acids
are classified into three categories: Aliphatic,
aromatic and heterocyclic. Aliphatic amino acids are
further classified into monoamino-monocarboxylic,
monoamino-dicarboxylic, diamino-monocarboxylic, sulphur
containing carboxylic acids. In neutral solution, amino
acids are zwitterionic, with a positive charge on the
nitrogen atom and a negative on the carboxyl group. All
amino acids have the same general structure except
proline.
Formation and classification of peptides
Peptide bond is formed by dehydration. Two amino acid molecules can
be covalently joined through a peptide bond to yield a dipeptide.
Peptide chain can be formed by the process of peptide bond formation
between joining amino acids. When there are a few amino acids in a
chain, usually 10-20, its called an oligopeptide. When there are
more than 20, it is called a polypeptide.
Structure and function of proteins
Proteins are among the fundamental molecules of biology and are
responsible for most of the complex functions that make life
possible. The amino acid sequence of a protein determines its 3D
structure. There are 4 classes of structure: Primary, secondary,
tertiary and quaternary. Primary structure of proteins refers to
linear number and order of the amino acids present. The ordered
array of amino acids in a protein confers regular conformational
forms upon that protein. These conformations constitute the
secondary structures of proteins. β- Sheets are either parallel or
anti parallel. α- helices and β sheet regions are connected by loop
regions. Tertiary structure describes the relationship of different
domains to one another within a protein. Quaternary structure
describes about proteins containing several distinct polypeptide
chains along with the non protein groups.
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