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| Box: Terminologies |
- Enantiomers: The dextro and leavo rotatory forms of a given amino acid, which are non-super-imposable mirror images of each other.
- Amino group: This consists of an NH2 group covalently bonded to the central carbon atom. Depending upon the pH of the surrounding medium, it either exists as NH2 or NH3+. Except for proline, which has a secondary amino group, all amino acids have only primary amino groups.
- Carboxyl group: A COOH group covalently bound to the central alpha carbon atom, which exists as either COOH or COO- depending on the pH of the surrounding medium.
- Peptide bond: Also known as the amide bond and is responsible for holding two amino acids together. In one bond, the carboxyl group of one amino acid is bound to the amino group of the other amino acid by means of a covalent bond, the formation of which involves loss of a water molecule.
- Psi) and Phi angles: Angle of rotation about the bond between the a-carbon atom and carboxyl and amino groups respectively. These angles determine which protein conformations will be favourable.
- Hydrogen bonds: Interaction between electropositive and electronegative atoms. They can be formed within a polypeptide chain or between different polypeptide chains.
- Electrostatic interactions: Attractive forces existing between oppositely charged groups/atoms, which can stabilize the protein structure.
- Hydrophobic interactions: Non-specific interactions between non-polar amino acid side chains, which acts to bury these hydrophobic residues away from a polar environment.
- Van der Waals forces: Weak attractive or repulsive forces caused due to changes in polarization.
- Disulphide bridges: Specific interaction and oxidation of thiol groups of cysteine residues in different regions of the polypeptide chain(s), which leads to formation of disulphide (S-S) bonds.
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