31.2 Morphology

 

Retroviruses are spherical and approximately 100 nm in size. The virion contains cone shaped nucleocapsid that encapsidates two copies of single stranded RNA about 10 Kb in size. In addition, capsid also contains three enzymes namely reverse transcriptase, proteases, and integrase. The nucleocapsid is covered by matrix protein which in turn is covered by an envelope containing two transmembrane glycoprotein called gp120 and gp 41.

 

Figure 31.1 Schematic representation of human immuno deficiency virus (HIV):

 

 

31.3 Virus entry

HIV enters the host cell by infecting the T- helper cells and macrophages which contain CD4 receptor. The viral gp120 binds to CD4 receptor to initiate the entry process. Coreceptors such as chemokine receptors (CCR5 and CXCR4) also assist in entry process. Different HIV serotypes use different coreceptors. Following the binding, the virus and cell membrane fuses releasing the nucleocapsid inside the cell.