p24(Core Protein):Protein that surrounds the inner core of
the virion. The core contains the virion nucleic acid (RNA) in
addition to enzymes that are necessary for the virion life cycle.
These include: reverse transcriptase (copies RNA to DNA),
intergrase ( inserts viral DNA into the genome[DNA] of the host
cell, and protease (necessary for the maturation of the virion
after budding from the host cell).
The size of the HIV genome is 9.2KB (9200 nucleic acid
base pairs).
- Structural Genes: a) GAG (matrix protein, core
protein, and nucleocapsid protein); b) POL (reverse
transcriptase, integrase, and protease); ENV (surface and
transmenbrane proteins.)
- Regulatory Genes: vif, vpr, vpu, rev, tat, and nef
- The LTR'S: Long Terminal Repeats of sequencies at both ends
of the virion nucleic acid that are nesessary for virion nucleic
acid replication.
Like all viruses, HIV is a genetic parasite. It uses the
host genome for it's own survival and perpetuation. The main
target cell (host cell) for HIV is a T4 Lymphocyte. This is a
white blood cell that is essential for the proper function of the
immune system. HIV inters this cell by binding to receptors that
are located on the surface of the T4 Lymphocyte. The receptors involved
are the CD4 molecule and, usually, a second receptor called a chemokine
receptor.
Once inside the host cell, HIV uses it's own enzyme (reverse
transcriptase) to copy it's RNA to DNA. This viral DNA moves into
the nucleus where it inserts or intergrates within the DNA of the
host cell. The viral DNA within the host DNA is called a
provirus.
When an infected T4 Lymphocyte is activated and begins
to divide or replicate itself, the virus replicates as well;
making copies of itself within the cell. These progeny virions
bud off from the infected cell taking a part of the cell
membrane. The host cell membrane (lipid and protein) becomes a
component of the outer structure of the virion that is called the
envelope. HIV inserts it's own proteins (gp120/gp40) within this
envelope. It is gp120/gp40 that is used by the virus to bind to
and infect other T4 Lymphocytes.
During the course of HIV infection, there is usually a
progressive decline in the number of T4 Lymphocytes. The
mechanism for this decline is not known. However, when infected
and noninfected cells are studied in culture, some of the cells
stick together and fuse forming giant multinucleated cells called
syncytia. These are abnornal cells. You can see what syncytia look like by clicking here.
Since the T4 Lymphocyte is necessary for immune system
function, an HIV infected individual that experiences a
continuous decline in the number of T4 Lymphocytes usually
becomes more suceptable to infection and disease.