Taxonomy

• A domain is the highest taxonomic rank and three are recognised: Bacteria, Archaea (group of prokaryotes) and eukarya
• Bacteria - Group of single-celled prokaryotes
• Bacteria features:

  • No membrane-bound organelles
  • Unicellular
  • Ribosomes smaller than in eukaryotic cells
  • Single loop of DNA made up of nucleic acids but no histones
• Archaea - A group of single-celled prokaryotes that were originally classified as bacteria which they resemble in appearance
• Archaea differ from bacteria because:

  • Their genes and protein synthesis are more similar to eukaryotes
  • Membranes contain fatty acid chains attached to glycerol by ether linkages
  • No murein in cell walls
  • More complex form of RNA polymerase
• Eukarya - A group of organisms made up of one or more eukaryotic cells
• Eukarya features:

  • Membrane-bound organelles
  • Membranes containing fatty acid chains attached to glycerol by ester linkages
  • If cells have cell wall, does not contain murein
  • Ribosomes are larger than in Bacteria and Archaea
• Eukarya domain is divided into four kingdoms:

  • Protocista
  • Fungi
  • Plantae
  • Animalia