The Human Immunodeficiency Virus (HIV) is an enveloped RNA retrovirus.Each virion contains the enzymes reverse transcriptase, protease and integrase and two copies of single-stranded RNA genome 9750 nucleotides long enclosed in a protein capsid. The capsid is surrounded by a lipid envelope which is of host-cell plasma membrane origin containing viral envelope proteins. The virus uses these attachment proteins (gp120) to gain entry into the host cell by binding to CD4 receptors on T-helper cells and fusing its outer envelope with the host cell plasma membrane.The capsid enters the host cell and is digested to release the viral RNA and the viral enzymes into the host cell.