A virus particle lacks cellular machinery necessary for its
replication and hence can only replicate inside a living particle
by hijacking its cellular machinery. It introduces its viral
material into the host cell and forces it to make copies of the
virus. A few mechanisms used by viruses to gain entry into the host
cell are listed below:
- Via membrane
fusion: The virus capsid has viral proteins that binds to
specific receptors expressed on the surface of host cells. This
mediates the attachment of viral particle to the host cell followed
by fusion of the viral envelope with the host cell membrane and the
contents are released into the cell.
- Via
Endocytosis: Endocytosis is the natural process through
which extracellular substances are engulfed by cells. Viruses binds
to specific receptors (Such as CD4 receptor which is bound by HIV)
on the host cells and the receptor (alongwith the virus) is
internalized and transported to the lysosomes. The acidic contents
of the lysosome opens up the viral capsid releasing out its genetic
contents. Thus viruses use this natural phenomenon of receptor
mediated endocytosis to gain access into the cell.