Question

Comment on the quaternary structure of proteins.

Answer 1

Quaternary structure:

1. Some proteins have two or more distinct subunits, or polypeptide chains, that might be the same or different.
2. A quaternary structure is created by how these protein subunits are arranged in three-dimensional complexes.

Types of proteins:

1. Proteins are classified into two main categories on the basis of higher levels of structure:
2. Fibrous proteins, which have polypeptide chains arranged in long strands or sheets,
3. And globular proteins, which have polypeptide chains folded into a spherical or globular shape.
4. Globular proteins frequently contain multiple types of secondary structure, whereas fibrous proteins typically consist mostly of one type of secondary structure.

Fibrous proteins:

1. Examples of fibrous proteins include keratin, collagen, and silk fibroin.
2. The structures in which fibrous proteins are present are made stronger or more flexible.
3. All fibrous proteins are insoluble in water because they contain a lot of hydrophobic amino acid residues both inside the protein and on its surface.

Globular proteins:

1. Different polypeptide chain segments (or several polypeptide chain segments) fold back on each other to form a globular protein, which has a spherical shape.
2. Enzymes, transport proteins, motor proteins, regulatory proteins, immunoglobulins, and proteins with several additional activities are examples of globular proteins.
3. They are water-soluble.
4. Example: Albumin, insulin, etc.