Viruses

Viruses are non-living particles made up of nucleic acid (RNA or DNA) enclosed in a protein coat or capsid.Some viruses such as the human immunodeficiency (HIV) virus also have a lipid envelope.There are attachment proteins on the surface of the virus which allow the virus to identify, attach and gain entry into specific cells.For example the HIV gp120 attachment glycoproteins attach to CD4 molecules on the surface of T-helper cells and gain entry into T-helper cells.Viruses infect all cells including bacteria. Viruses that infect bacteria are called bacteriophages.Viruses are much smaller than bacterial cells. They are about 20-300nm in diameter.HIV virus infects human T-helper cells.1. Attachment proteins attach to receptors on helper T cell2. Nucleic acid/RNA enters cell.3. Reverse transcriptase converts RNA to DNA.4. Viral protein for the capsid and enzymes are produced.5. Virus particles are assembled and released from the cell.