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Introduction, Classification, Chemical Nature and Biological Role of Amino Acids and Proteins

Molecularly, amino acids are recognized as a separate group of neutral compounds, primarily due to their ampholytic properties, but also biochemically

Amino acids


Molecularly, amino acids are recognized as a separate group of neutral compounds, primarily due to their ampholytic properties, but also biochemically, as they are components of proteins. A carboxylic acid with an aliphatic primary amino group positioned in the α position with a characteristic stereochemistry is an amino acid. The biosynthesis of proteins is controlled by a gene-control system. Proteins are made up of amino acids. The number of amino acids in the world is greater than 300, but only 20 of them are encoded by genes and found in standard forms in proteins. Amino acids are also found in substances other than proteins. The posttranslational modification of some residues occurs after proteins have been synthesized; the non-translational modification of others can occur in any living cell.


Based on the R group
  • Nonpolar and aliphatic amino acids: Nonpolar and hydrophobic R groups are present in these amino acids. These amino acids are glycine, leucine, alanine, isoleucine, methyl, valine, and proline.
  • Aromatic amino acids - There are a few aromatic amino acids, which are relatively nonpolar (hydrophobic). These include phenylalanine, tyrosine, and tryptophan. These amino acids can interact with hydrophobic molecules.
  • Polar, uncharged amino acids - Unlike nonpolar amino acids, these amino acids contain more hydrophilic R groups or are more soluble in water, because they make hydrogen bonds with water. Asparagine, cysteine, threonine, cysteine, and glutamine all belong to this class of amino acids.
  • Acidic amino acids - Acidic or negatively charged amino acid R groups are characteristic of these acids. Aspartic acid and glutamic acid are examples.
  • Basic amino acids - Those that carry positive charges or have a basic R-group. Arginine, histidine, lysine are some of the common examples.

Chemical nature

There are 20 alpha-amino acids among the common amino acids. Besides a carboxyl group and an amino group, they also have a side chain (an R group) attached to the α-carbon.

There are some exceptions, however:
  • amino acids without side chains, such as glycine. There are two hydrogens on its α -carbon.
  • Proline contains nitrogen in a ring form.
  • Aside from the distinctive side chain, each amino acid also has an amine and an acid group at one end, and a side chain between them. Although all amino acids have the same backbone, each has a different side chain.
  • In all but one amino acid, the α-carbon is an asymmetric carbon, so all but one amino acid is an amino acid of the L-configuration. A glycine molecule is neither optically active nor L because it contains no asymmetric carbon atom.

Biological role

1. 20 amino acids are particularly important because they contain peptides and proteins and are regarded as the building blocks of all living things.
2. Proteins' three-dimensional structure is determined by the linear sequence of amino acid residues, and their functions by their structure.
3. For the body to maintain health, amino acids are necessary. These acids contribute to:
  • Synthesis of hormones
  • Muscle structure
  • Healthy functioning of the nervous system
  • Organ health
  • The normal cellular structure
4. Proteins and nitrogen-containing compounds (e.g., purines, heme, creatine, and epinephrine) are synthesized from amino acids by various tissues. Or, amino acids are oxidized in the body to create energy.
5. Nitrogen-containing substrates and carbon skeletons are formed during the breakdown of dietary and tissue proteins.
6. A nitrogen-containing substrate is used to biosynthesize purines, pyrimidines, neurotransmitters, hormones, porphyrins, and non-essential amino acids.
7. The carbon skeleton is a fuel source for citric acid metabolism, gluconeogenesis, or the synthesis of fatty acids.
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Ankur Choudhary is India's first professional pharmaceutical blogger, author and founder of, a widely-read pharmaceutical blog since 2008. Sign-up for the free email updates for your daily dose of pharmaceutical tips.
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