Akaryotes

• Viruses are acellular- they are not cells as they are non-living.
• Viruses consist of nucleic acid (genetic material)  surrounded by protein. They do not contain any organelles.
• • The genetic material can be DNA or RNA.
  • It is used within the host cell to make the proteins needed to produce more of the virus.
• • The attachment proteins are made out of proteins.
  • They have a specific complementary shape to receptors and are used to attach to host cell receptors.
• • The capsid is made out of protein.
  • It protects the nucleic acid.
• Viruses contain an enzyme called reverse transcriptase.
• As they are not alive, viruses do not undergo cell division. Instead they inject their DNA or RNA into the host cell. The host cell then produces the viral components which are assembled into new viruses.
• • In order to inject their DNA/RNA, viruses first have to attach to the host cell surface.
  • To do this they use their attachment proteins to bind to complementary receptor proteins on the cell surface membrane of the host cell.
  • Different viruses have different attachment proteins and therefore bind to different receptor proteins on host cells. As a result some viruses can only infect one type of cell, while others can infect lots of different cells (e.g. influenza) 
• 1. Virus attaches itself to host cell receptor proteins.
  2. Genetic material is released into the host cell.
  3. Genetic material and proteins are replicated by host cell 'machinery'.
  4. The viral components assemble.
  5. The replicated viruses are released from the host cell.
• An example of how a virus replicates after it has inserted itself into a host cell.

  1. Viral RNA is converted into viral DNA using the enzyme reverse transcriptase.
  2. The viral DNA is inserted into the host DNA.
  3. The DNA is transcribed into viral mRNA
  4. Viral mRNA translated into new viral proteins.
  5. These proteins are assembled into new viral particles.
  6. These 'bud off' the cell membrane of the host cell, exit the cell and enter the surrounding fluid.