PROKARYOTIC CELLS AND VIRUSES

• What are features of prokaryotic cells?

  Flagella for movement,

  plasmid (small circular DNA, usually contain genes for antibiotic resistance),

  long loop of chromosomal DNA found in nucleoid region,

  murein cell wall,

  capsule (mucus that protects the cell from its environment/ immune system of host),

  plasma membrane (cell surface membrane),

  ribosomes (70s),

  may contain chlorophyll and/or enzymes for respiration embedded in the membrane
• What are features of viruses?

  Genetic material (DNA/RNA), capsid protein encapsulates DNA,

  Matrix (mesh of fibres),

  lipid envelope (helps enter host cells, not in all viruses),

  attachment proteins that attach to receptors on host cell to gain access
• What does a virus need to survive?

  It is acellular (non living) needs a host to survive
• What is the size of a virus?

  It is smaller than bacteria, 20-300nm
• What is the size of a prokaryote?

  0.1-10um
• PROKARYOTIC CELL

  
• VIRUS

  
• Why is a virus non-living?

  They can only replicate/reproduce inside a host cell, cannot carry out metabolic processes without a host
• Why can viruses not be destroyed by antibiotics?

  as they do not have:

  • cell walls
  • ribosomes
  • enzymes

  so there is nothing for the antibiotics to act on
• Virus replication

  • attachment proteins bind to complementary receptors on host cell surface
  • viral DNA/RNA is injected into host cell
  • host cell uses its own ribosomes to synthesise viral proteins and nucleic acids
  • host ER synthesises lipids for lipid envelope (HIV)
  • new viral particles are assembled
  • viruses released by:
  • cell lysis (bursting)
  • budding (takes host membrane, forms virus envelope)
• How does HIV replicate?

  • infects helper T cells and uses machinery of cell to replicate
  • viral RNA enters cell
  • viral reverse transcriptase produces DNA copy of viral RNA
  • DNA copy inserted into chromosomes of cell
  • each time cell divides it copies viral DNA
  • HIV proteins produced from viral DNA, used to build new HIV particles
  • thousands produced, killing helper T cell, new particles go on to infect other T-helper cells
• What does HIV do to the immune system?

  • reduces number of T cells in immune system, so:
  • B cells no longer activated
  • no antibodies produced
  • decreases body's ability to fight off infections, leading to AIDS