Prokaryotes and viruses

• Cell wall

  • Made up of murein
  • Physical barrier that excludes certain substances and protects against damage and osmotic lysis
• Capsule

  • Layer of slime
  • Protects bacteria from other cells and helps groups of bacteria stick together
• Cell-surface membrane

  Acts as a different permeable layer which controls entry and exit of chemicals
• Circular DNA

  Possesses genetic information for replication of bacterial cells
• Plasmid

  • Small circular pieces of DNA
  • Possesses genes that aid the survival of bacteria, e.g. by producing enzymes that break down antibiotics
• Prokaryotic cells

  • No nucleus
  • DNA not associated with proteins
  • Some DNA in form of circular strands called plasmids
  • No membrane-bound organelles
  • Smaller ribosomes (70S)
  • Cell wall made up of murein
  • May have slime layer called capsule
• Eukaryotic cells

  • Distinct nucleus with nuclear envelope
  • DNA associated with proteins called histones
  • No plasmid and DNA is linear
  • Has membrane-bound organelles, such as mitochondria
  • Chloroplasts presents in plants and in algae
  • Larger ribosomes (80S)
  • Cell wall made up of cellulose (chitin in fungi)
  • No capsule
• Viruses

  • Acellular, non-living particles
  • Smaller than bacteria
  • Contain nucleic acids such as DNA or RNA - enclosed within capsid
  • Can only multiply inside living host cells
  • Lipid envelope - present in some viruses (like HIV) - has attachment proteins used to identify and attach to host cells