Immunity/viruses

• Viruses are acellular because they lack a cell wall/membrane. They are inactive outside a host and can only reproduce when they are in a host. Viruses cannot carry out respiration
• Antibiotics are ineffective against viruses because; antibiotics breakdown the murein cell wall and cell membrane in bacteria which are both absent in viruses. Antibiotics also target bacterial enzymes and ribosomes which again viruses do not have.
• Structural features found in all virus include: attachment proteins, capsid, lipid envelope
• HIV replication

  1. Attachment proteins attaches to receptors on helper T cell
  2. Capsid un coats/releases genetic material (viral RNA)
  3. Reverse transcriptase converts viral RNA to (viral) DNA
  4. Viral DNA inserted into human DNA/ viral proteins produced/ viral enzymes
  5. Viral proteins assembled into new viruses which are released from cell (bud)
• Antigens are used by the immune system to identify:

  • pathogens
  • abnormal body cells(e.g. tumour cells)
  • toxins
  • cells from other individuals from the same species (e.g. transplant)