Viruses are infective organism that infect living cells in order to reproduce and live. The word virus is derived from a Latin word which translates as “Poison” or “Toxin”. Viruses typically consist of a nucleic acid molecule in a protein coat and are alive only inside the body of a host. Alone, they are rather inert. For about 100 years, the scientific community has repeatedly changed its collective mind over what viruses are. First seen as poisons, then as life-forms, then biological chemicals, viruses today are thought of as being in a gray area between living and nonliving: they cannot replicate on their own but can do so in living cells and can also affect the behavior of their hosts profoundly.
Among the various types of viruses, HIV is a retrovirus. Retrovirus is a family of incased viruses that replicate in a host cell through the process of reverse transcription. A retrovirus is a single-stranded RNA virus that stores its nucleic acid in the form of an mRNA genome and targets a host cell as an obligate parasite. The virus uses an enzyme reverse transcriptase to make DNA from its RNA strand as it enters the host cell. The newly formed virus DNA is incorporated in the host’s DNA using an enzyme called integrase. After it is inserted in the host’s genome, it is called a provirus. The cell then unknowingly transcribes the virus’ DNA and translated proteins necessary for the virus. The virus is difficult to detect until it affects the human cell.
An interesting thing about HIV is that while other viruses contain the gene for the enzymes they require within their nucleic acids, HIV directly has the enzyme RNA Transcriptase. The activity of the enzyme enables the genetic information of HIV to become integrated permanently into the genome (chromosomes) of a host cell.
Viruses are only active inside the body of the host. They are otherwise considered dead. The above figure shows a spherical retrovirus with all the viral structures.
HIV stands for Human Immunodeficiency Virus. The virus is spherical in shape with an average diameter of around 120 nm. The outer coat of the virus- the viral envelope, is composed of two layers of lipids, taken from the membrane of a human cell when a newly formed virus particle buds from the cell. Embedded throughout the viral envelope are proteins from the host cell, as well as 72 copies (on average) of a complex HIV protein known as Env. These Env copies protrude or spike through the surface of the virus particle (called a “virion”). Env consists of a cap made of three molecules called glycoprotein 120 (gp120), and a stem consisting of three molecules called gyclycoprotein 41 (gp41) that anchor the structure in the viral envelope. Much of the research to develop a vaccine to prevent HIV infection has focused on these envelope proteins.
The outer coat of protein that surrounds the virus is the capsid. It surrounds the two single strands of HIV RNA which codes for all...