4. Name the four different types of interactions responsible for creating tertiary structures in proteins and elaborate the same.
answer :
TERTIARY STRUCTURE :
A protein’s distinctive three-dimensional shape, or tertiary
structure, results from interactions between residues that
are brought together as the chain bends and folds in space.
The residues that interact with one another are often far apart
in the linear sequence. In contrast to secondary structures,
which involve only hydrogen bonds between backbone components, tertiary structures form using a variety of bonds and
interactions between R-groups or between R-groups and the
backbone.
Five types of interactions involving R-groups are particularly
important:
1. Hydrogen bonding : Hydrogen bonds form between polar
side chains and opposite partial charges either in the peptide
backbone or other R-groups.
2. Hydrophobic interactions: In an aqueous solution, water
molecules interact with the hydrophilic polar side chains of a
polypeptide, forcing the hydrophobic nonpolar side chains to
coalesce into globular masses. When these non polar R-groups
come together, the surrounding water molecules form more
hydrogen bonds with each other and the polar residues on
the surface of the protein, increasing the stability of their
own interactions and the disorder of the aqueous solution.
3. van der Waals interactions: Once hydrophobic side chains
are close to one another, their association is further stabilized by electrical attractions known as van der Waals
interactions. These weak attractions occur because the
constant motion of electrons gives molecules a tiny asymmetry in charge that changes with time. If nonpolar molecules get extremely close to each other, the minute partial
charge on one molecule induces an opposite partial charge in
the nearby molecule and causes an attraction. Although the
interaction is very weak relative to covalent bonds or even hydrogen bonds, a large number of van der Waals interactions can significantly increase the stability of the structure.
4. Covalent bonding: Covalent bonds can form between the
side chains of two cysteines through a reaction between the
sulfhydryl groups. These disulfide (“two-sulfur”) bonds
are frequently referred to as bridges, because they create
strong links between distinct regions of the same polypeptide
or two separate polypeptides.
5. Ionic bonding:Ionic bonds may form between groups that
have full and opposing charges, such as the ionized acidic and
basic side chains highlighted on the right
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