Question

1. Movement of viruses inside the cell (for example, transport to the nucleus) is typically mediated by what cellular structures?
2. Movement of viruses and viral genomes into the nucleusoccurs through what cellular structures?

Answer 1

Viruses are not proper cells. They are called 'particles' and consist of nuclear material [ DNA or RNA ] enclosed within a protein envelop which does not have any outer envelope. They enter the host cell through endocytosis. When a virus comes in contact with a host cell, it attaches to specific receptors on the host cell membrane. The virus particles are then endocytosed and enter the endosomes. The viral genetic material is injected into the cytoplasm. The viral genetic material enters the host nucleus and incorporates itself into the host genetic material and induces it to replicate the viral genome.

Viral entry into the host cell can be by the three ways mentioned below-

1. Membrane fusion- in this the cell membrane of the host is punctured and made to further connect with the unfolding viral envelope.

2. Endocytosis- the host cell takes in the viral particle through the process of endocytosis, engulfing the virus like it would a food particle.

3. Viral penetration- the viral capsid or genome is injected into the host cell's cytoplasm.

When the virus are endocytosed they are enclosed within vesicles called endosomes. The endosomes transport the virus through the cell and ensure that no trace of the virus is left on the surface, so that the immune system is not activated.

So, endosomes are the cellular vesicles which transport the viral genome into the nucleus.