Natalie Taylor
A-level Biology
Viruses: HIV
HIV stands for human immunodeficiency virus, this is a type of virus, known as a
retrovirus, that damages the cells in your immune system, specifically T helper cells,
that then weaken an individual's ability to fight everyday infections and viruses. The
people infected with HIV usually experience a short flu-like illness, the main
symptoms include: raised temperature, sore throat or body rashes, that can last
between two to six weeks once a person has a HIV infection. The structure of this
virus is a spherical shape that has an envelope made from lipids and glycoproteins.
Inside the virus there is a cone-shaped capsid that contains strands of RNA and an
enzyme called reverse transcriptase.
HIV spreads when bodily fluids mix from an infected person to another. This can
happen either during sexual intercourse, when a blood transfusion is given from the
infected person into an uninfected person, when a drug user shares a needle with an
infected person or from an infected mother to her unborn baby through the placenta.
Once one of these ways has occurred, it then allows HIV to get into the body and
enter the bloodstream. When in the bloodstream, it will infect a certain type of T cell
known as a T helper cell. HIV only infects T helper cells because the receptor
proteins in the cell surface membrane of T helper cells have a complementary fit to
the proteins on HIV. So once HIV is attached to the surface of the T helper cell, the
viral RNA enters the cell, and the viral reverse transcriptase enzyme makes a DNA
copy of the viral RNA. This DNA copy is then inserted into the T helper cell’s DNA
and everytime the T helper cell divides copies of the viral DNA inserted do as well
but during this time the cell remains normal as the HIV is inactive. During this stage
an individual is said to be HIV-positive as they are infected with the virus and have
antibodies against it in their blood. However, antibodies cannot work against HIV
because HIV mutates rapidly so by the time a B cell learns to produce antibodies to
fight against one version of the virus, a new viral mutant will have most likely already
taken over; making the antibody ineffective. Also, the receptors on the surface of the
visus are coated with a thick sugary substance that antibodies cannot penetrate, this
then allows the virus to escape being neutralised.
For a long while, which could be many years, the viral DNA can be inactive for but
eventually the viral DNA will become active. When this happens it takes over any of
the T helper cells that it has already infected and causes them to make many more
HIV particles. This activation results in the T helper cells dying that causes them to
release thousands of new HIV particles that then go one to infect new T helper cells,
meaning gradually this virus will destroy many T helper cells in the body. T helper
cells are important for an individual to have as they are used during the body’s
immune response to a pathogen or its antigens that may have entered an their body.
T helper cells stimulate T cytotoxic cells to be produced as well as cause B cells to
A-level Biology
Viruses: HIV
HIV stands for human immunodeficiency virus, this is a type of virus, known as a
retrovirus, that damages the cells in your immune system, specifically T helper cells,
that then weaken an individual's ability to fight everyday infections and viruses. The
people infected with HIV usually experience a short flu-like illness, the main
symptoms include: raised temperature, sore throat or body rashes, that can last
between two to six weeks once a person has a HIV infection. The structure of this
virus is a spherical shape that has an envelope made from lipids and glycoproteins.
Inside the virus there is a cone-shaped capsid that contains strands of RNA and an
enzyme called reverse transcriptase.
HIV spreads when bodily fluids mix from an infected person to another. This can
happen either during sexual intercourse, when a blood transfusion is given from the
infected person into an uninfected person, when a drug user shares a needle with an
infected person or from an infected mother to her unborn baby through the placenta.
Once one of these ways has occurred, it then allows HIV to get into the body and
enter the bloodstream. When in the bloodstream, it will infect a certain type of T cell
known as a T helper cell. HIV only infects T helper cells because the receptor
proteins in the cell surface membrane of T helper cells have a complementary fit to
the proteins on HIV. So once HIV is attached to the surface of the T helper cell, the
viral RNA enters the cell, and the viral reverse transcriptase enzyme makes a DNA
copy of the viral RNA. This DNA copy is then inserted into the T helper cell’s DNA
and everytime the T helper cell divides copies of the viral DNA inserted do as well
but during this time the cell remains normal as the HIV is inactive. During this stage
an individual is said to be HIV-positive as they are infected with the virus and have
antibodies against it in their blood. However, antibodies cannot work against HIV
because HIV mutates rapidly so by the time a B cell learns to produce antibodies to
fight against one version of the virus, a new viral mutant will have most likely already
taken over; making the antibody ineffective. Also, the receptors on the surface of the
visus are coated with a thick sugary substance that antibodies cannot penetrate, this
then allows the virus to escape being neutralised.
For a long while, which could be many years, the viral DNA can be inactive for but
eventually the viral DNA will become active. When this happens it takes over any of
the T helper cells that it has already infected and causes them to make many more
HIV particles. This activation results in the T helper cells dying that causes them to
release thousands of new HIV particles that then go one to infect new T helper cells,
meaning gradually this virus will destroy many T helper cells in the body. T helper
cells are important for an individual to have as they are used during the body’s
immune response to a pathogen or its antigens that may have entered an their body.
T helper cells stimulate T cytotoxic cells to be produced as well as cause B cells to
