Question

What determines quaternary structure?

Answer 1

Levels of protein structure:

There are mainly four types of protein structure-

1. The primary structure is the chain of amino acids held together by covalent and peptide bonds.
2. Almost all known genetic disorders (sickle cell anaemia, cystic fibrosis, etc) are caused by mutations that initially alter the primary protein structures.
3. This further leads to secondary, tertiary, & quaternary structure changes.
4. Secondary structure refers to local folded structures that form within a polypeptide due to interactions between atoms (mostly amine and the carboxyl group of the peptide link) of the backbone.
5. They occur in the form of α – helix or β – pleated sheets.
6. Tertiary structure is formed by further folding of the secondary structure of the protein.
7. Such folding is stabilized via hydrogen bonds, disulfide bonds, electrostatic forces, and van der Waals forces.
8. This structure arises from further folding of the secondary structure of the protein, giving rise to fibrous and globular shapes.
9. Quaternary structure is the spatial arrangement of various tertiary structures.
10. Proteins like hemoglobin, DNA polymerase, and ribosomes are composed of two or more polypeptide chains(called sub-units).
11. The spatial arrangement of these subunits with respect to each other is known as quaternary structure.
12. The stability of the quaternary structure is determined by non-covalent forces.

Non-covalent forces/bonds:

1. These are found mostly between macromolecules.
2. In this type of interactions, there is no sharing of electron pairs and it is mostly used to bond large molecules (proteins and nucleic acids).
3. They are weaker than covalent bonds.
4. Example- Hydrogen bonds, Ionic forces, Van der Waals interactions, etc.