HIV Structure – Life Cycle, Genome & Functions in PPT / PDF

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 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.

This enzyme integrates the DNA produced by reverse transcriptase into the host's genome.

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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