Question

Describe the general structure of a virus, indicating what features all viruses have and what features are unique to certain viruses. What controls the tropism of a virus?

Answer 1

In general all viruses contain the following components:

• A viral genetic material that is nucleic acid genome (either RNA or DNA).
• An enclosing protein coat called the capsid protein. (The arrangement so called as the nucleocapsid).
• A lipid envelope that holds the virus in tact.

All viruses do have the nucleopcapsid that is made of repeating structural subunits in the form of symmetrical helix or icosahedron shape. These structures recognize the signals corresponding to the viral genome and differentiate between self and host genome.

The lipid layer in a virus consists of the viral proteins, including the glycoproteins and matrix proteins that link the lipid layer and the capsid. These glycoproteins are essential at the time of interaction with host and fuse with host cells thereby invading the host organism.

The genome of the virus may be an RNA or DNA (either single stranded or double stranded).

In general, viruses are non-living in the external enviroment. It is when they interact with and enter into a host, they get activated. The lipid glycoproteins interact with the cell surfaces fuse with them and release their genetic material into the host. During, the cellular replication processes, the host cells start replicating the viral DNA and new viral particles are produced. Slowly, the virus takes the control over the host.

Some RNA virus, a group called the retroviruses possess an enzyme in addition called the reverse transcriptase. The virus containing singled -stranded RNA uses its enzyme reverse transcriptase and the host DNA replication mechanism to produce a second strand containing its own genetic material. Such viruses, are difficult to be recognized by our immune response (tend to escape immune response). Since they produce their DNA after entering the host.

The viral tropism is controlled by the mutation rate of the virus. The tropism in general refers to the capability of virus to interact with different types of cells. Only if a virus has a higher degree of tropism can it succeeing in invading host, and cause infection.