Revision - Main characteristic of Viruses.

NB this is my own revision and I cannot promise accuracy - do research.

Question:
a)  Discuss in depth the main characteristics of viruses

Viruses are not classed as living things as they cannot replicate without a host.  They do not have a metabolism.
Viruses spread using cells.
They have a protein coat called a capsid.
Viruses are very small, much smaller than bacteria.
They are difficult to treat.

b) Give a detailed account of the main events involved in a typical virus life cycle

A virus enters the body and locates a host cell.  As it fuses, it uses the protein coat to enter the cell.  Here,  it enters either a lytic cycle or a lysogenic cycle .  Nucleic acid will be used to reform DNA/RNA and change the genetic material of the cell.
The lytic cycle then sees the cell erupt making copies of the other cells.  Leaving holes in the cell membrane gives ease to apoptosis of the cell as it cannot survive without the membrane.
The lysogenic cycle uses DNA to hide in cells until immune comprimisation occurs.

c)  List factors contributing to viral pathogenicity and to the nature and severity of viral diseases.

Pathogenicity refers to the ability of an organism to cause disease (i.e. harm the host).  This ability represents a genetic component of the pathogen and the damage done to the host is a property of the host-pathogen reactions.

Natural killer cells are lymphocytes, they recognise this virus and kill.
The severity of viral diseases is dictated by the immune response. In several immune deficiency diseases including AIDS NK cell function is abnormal.
NK cells binds to cell and releases toxins which produces holes int he target cells membrane creating apoptosis.
NK cells may also contribute to immunoregulation by recreating high levels of influential lymphokines.