Prokaryotic and eukaryotic cells

• Prokaryotic cells


  May have been among the earliest forms of life on Earth
• Early prokaryotic cells


  • Adapted to living in extremes of salinity, pH and temperature
• Extremophiles


  Organisms that can survive in extreme environments
• Environments where extremophiles can be found

  • Hydrothermal vents
  • Salt lakes
• Extremophiles are usually of the domain Archaea and more recently they have been found in more hospitable environments such as soil and the human digestive system
• Prokaryotic organisms


  • Always unicellular with a relatively simple structure
  • DNA is not contained within a nucleus
  • Few organelles and the organelles they do have are not membrane-bound
• DNA in prokaryotes


  Fundamentally the same as in eukaryotes but packaged differently
• Prokaryotic DNA


  • Generally only have one molecule of DNA, a chromosome, which is supercoiled to make it more compact
  • Genes on the chromosome are often grouped into operons, meaning a number of genes are switched on or off at the same time
• Ribosomes in prokaryotic cells


  Smaller than those in eukaryotic cells
• Eukaryotic ribosomes


  Designated 80S
• Prokaryotic ribosomes


  Designated 70S
• Both 80S and 70S ribosomes are necessary for protein synthesis, although the larger 80S ribosomes are involved in the formation of more complex proteins
• Cell wall of prokaryotic cells

  Made from peptidoglycan, also known as murein, which is a complex polymer formed from amino acids and sugars
• unicellular organisms can be classed into 2 evolutionary domains 


  Archae and Bacteria
• Nucleus


  • Present in eukaryotic cells
  • Not present in prokaryotic cells
• DNA


  • Linear in eukaryotic cells
  • Circular in prokaryotic cells
• DNA organisation


  • Associated with proteins called histones in eukaryotic cells
  • Proteins fold and condense DNA in prokaryotic cells
• Plasmids


  • Circular DNA present in prokaryotic cells
  • Extra-chromosomal DNA
• Organelles

  • Membrane-bound and non-membrane bound in eukaryotic cells
  • Non-membrane bound in prokaryotic cells
• Cell wall


  • Present in prokaryotic cells and some eukaryotic cells (fungi, plants)
  • Not present in animal cells
• Ribosomes


  • Smaller, 70S in prokaryotic cells
  • Larger, 80S in eukaryotic cells
• Cytoskeleton


  • Present in prokaryotic cells
  • More complex in eukaryotic cells
• Reproduction


  • Binary fission in prokaryotic cells
  • Asexual or sexual in eukaryotic cells
• Cell type


  • Unicellular in prokaryotic cells
  • Unicellular and multicellular in eukaryotic cells
• Cell-surface membrane


  • Present in both prokaryotic and eukaryotic cells
• Peptidoglycan


  • Present in prokaryotic cell walls