Presentation Notes on Human Immunodeficiency Virus Cell Structure
with Image / Diagram in Word Format
HIV
Structure/ MORPHOLOGY OF HIV/ How does HIV look like?
It is around 120 nm in diameter (120 billionths of a meter;
around 60 times smaller than a red blood cell) and roughly spherical. HIV
consists of a cylindrically shaped nucleoid and the surrounding proteins. They are both enclosed a lipid, fatty, envelope.
The nucleoid is composed of two proteins known as Nucleoid Core Protein (p24)
and Matrix Core Protein (p17). Inside the nucleoid are Viral Genomic RNA and
the associate enzyme called reverse transcriptase (RT).
Outside the envelope attaches two proteins known as
Transmembrance Glycoprotein (gp41) and Envelope Glycoprotein (gp120).The
function of these two outer layer proteins is to enable HIV to bind and fuse
with another target cell. The individual particles (virions) of human
immunodeficiency virus (HIV) are spherical in shape and approximately one
ten-thousandth of a millimeter in diameter. Their envelope consists of a
bilayer of fat molecules (lipids) derived from the external membrane of the
host cell and contains proteins with carbohydrate side-chains (viral envelope
glycoproteins, gp).
One of the components of these mushroom-shaped envelope
proteins is the glycoprotein gp41 (transmembrane glycoprotein), which is
located in the viral membrane, and another is the gp120 "spike",
which projects out from the membrane like a cap. The envelope surrounds a viral
core that includes the outer protein structure p18 and the inner protein p24.
Within this capsid shell and surrounded by p7 and p9
proteins is the viral RNA (ribonucleic
acid). This consists essentially of three genes: env for the viral envelope
protein, gag for the RNA-containing core, and pol for the viral enzymes
protease, reverse transcriptase, and RNase H. Other genes code for small
proteins that are involved in the regulation of gene expression.
The genetic material of HIV, a retrovirus, takes the form of
RNA rather than the DNA (deoxyribonucleic acid) of human cells. In order for
HIV to replicate, its enzyme reverse transcriptase, which consists of
polymerase and ribonuclease, must first produce a DNA version using the RNA as
a template. In this stepwise process the polymerase transcribes the viral
genome into DNA, the ribonuclease digests the original RNA strand, and the
polymerase produces a complementary strand of DNA. The viral DNA produced in
this way now migrates to the nucleus of the host cell and is inserted into the
human genome with the aid of the enzyme integrase. Subsequently it is
replicated with each cell division.
If you were to look at a HIV virus particle under a
microscope, it would look something like this:
The size of the particle is around 0.0001mm. There are two main parts, essentially:
The size of the particle is around 0.0001mm. There are two main parts, essentially:
the inner core (the "pill-shaped" section in the
diagram), and the viral membrane.
The viral membrane encloses the particle, and has about nine
or ten gp160 spikes embedded in it which are involved in binding and membrane
fusion when the virus particle attaches to a cell. The inner core is the
"payload" of the virus, containing the viral RNA and some enzymes (reverse
transcriptase, protease, integrase).
Reverse
transcriptase
Common to all retroviruses, this enzyme transcribes the
viral RNA into double-stranded DNA.
Integrase
This enzyme integrates the DNA produced by reverse transcriptase
into the host's genome.
Protease
A protease is any enzyme that cuts proteins into segments.
HIV's gag and pol genes do not produce their proteins in their final form, but
as larger combination proteins; the specific protease used by HIV cleaves these
into separate functional units. Protease inhibitor drugs block this step.
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