Question

what is the capsid of a virus, and what is its function; how are the two types of capsids constructed?

Answer 1

A capsid is the protein shell of a virus. It consists of several oligomeric structural subunits made of protein. The capsid encloses the genetic material of viruses.

The capsid has three functions:

1. protects the nucleic acid from digestion by enzymes
2. contains special sites on its surface that allow the virion to attach to a host cell
3. provides proteins that enable the virion to penetrate the host cell

The two major types of capsid:

1. Helical - Helical capsids are usually formed from one protein that interlocks to form a helix-like structure around the viral genome.
2. Icosahedral - Many animal viruses have an icosahedral structure. They are often formed by either one to three repeating subunits of capsid proteins.