Viruses and HIV

Viruses

• Viruses are acellular (not cells) and are non-living
• Viruses have a very simple structure - 
  • a capsid (protein coat) surrounding genetic material (DNA or RNA)
  • attachment proteins (to allow entry into host cells)
• Viruses are only capable of reproducing inside a host cell
• By injecting their nucleic acid into the host cell, incorporating their DNA into the host cell DNA and then taking over protein synthesis
• This allows more new virus particles to be made
• These then leave the cell to infect new host cells (often killing them)
• Some viruses take a layer of host cell membrane around them as they leave, these are called enveloped viruses
• Viruses that affect bacteria are called bacteriophages

Replication inside a Host Cell:

• Stage one - 
  • attachment to specific receptor proteins on T helper cells
  • capsid enters T helper cell
  • capsid releases RNA and reverse transcriptase into cell
• Stage two - 
  • reverse transcriptase makes a single stranded DNA copy from the viral RNA 
  • then a double stranded DNA copy is made
  • DNA polymerase is used
  • viral DNA is inserted into host DNA in the nucleus
• Stage three -
  • cell enzymes and organelles are used to make…