What is the Difference Between Capsid and Envelope?

The capsid and envelope are two structural components of a virus that play crucial roles in its survival and infection process. The main differences between them are:

Composition: The capsid is a coat made up of proteins, while the envelope is a membrane made up of lipids.
Function: The capsid protects the viral genome, which can be RNA or DNA, while the envelope covers the nucleocapsid (viral genome + capsid) and protects it during its life cycle when traveling between host cells.
Presence: The capsid is present in all viruses, while the envelope is present only in some viruses, known as enveloped viruses.
Stability and Resistance: Both structures determine the method of viral entry into and exit from host cells, as well as the stability and resistance of the virus.

In summary, the capsid is a protein coat that protects the viral genome, while the envelope is a lipid membrane that covers the nucleocapsid and protects it during its life cycle when traveling between host cells. Not all viruses have an envelope, and only enveloped viruses possess one.