lecture 1

• Origin of Earth


  4.6 billion years
• Eons (eras) of geologic time

  • Archaean
  • Proterozoic
  • Phanerozoic
• Prokaryotes were the Earth's only inhabitants from 3.5 billion years ago to 2 billion years ago
• Evidence of prokaryotes comes from fossils (photosynthetic prokaryotes)
• Prokaryotes changed the biosphere and caused the 'oxygen revolution'
• Some prokaryotes that could use oxygen started the evolution of 'cellular respiration'
• The first single celled eukaryotic cells appeared

  About 2.1 billion years ago
• Larger eukaryotic cells evolved from smaller prokaryotic cells

  
• Multicellular organisms formed from lots of unicellular eukaryotic forms
• Plants and fungi colonized land about 500 million years ago
• The most widespread and diverse land animals are insects, spiders and vertebrates
• Humans diverged from other primates around 6-7 million years ago
• Eukaryotes evolved from prokaryotes living inside one another
• Even today, a prokaryote can live in the eukaryote cell (called the endosymbiotic bacteria)
• New organisms are being discovered every day and taxonomy provides a tool for clarifying the evolution of organisms
• Fossils provide evidence of what was around millions of years ago
• Raul Cano (1995) found growing Bacillus sphaericus and other unidentified microorganisms embedded in fossilized plants for millions of years
• The 'All Species Inventory' project aims to identify every species on the planet within 25 years
• There are over 1.5 million different organisms but could be over 7-100 million
• Carolus Linnaeus (1735) introduced a class system of just two kingdoms (Plants and Animals)
• Ernst Haeckel (1866) proposed the Protista kingdom which the bacteria, protozoa, algae and fungi were classed
• DNA sequencing discovered that the fungus's DNA was actually closer to animals than it was to plants
• In 1959, the Fungi Kingdom was established
• In 1937, the definition of 'Prokaryotes' was given where the nuclear material is not surrounded by a nuclear membrane
• In 1968, Robert Murray proposed the 'Prokaryotae or Monera' Kingdom
• The five kingdoms founded by 1969


  • Animals (eukaryote)
  • Plants (eukaryote)
  • Fungi (eukaryote)
  • Protists (eukaryote e.g. protozoa and algae)
  • Prokaryotae or Monera (prokaryote e.g. bacteria)
• In 1978, Carl Woese proposed having another classification level ABOVE kingdom and called it 'domain'
• Woese believed that the two prokaryote types called the 'bacteria and archaea' should have their own domains

  
• The three domains proposed by Carl Woese

  • Bacteria
  • Archaea
  • Eukarya

  
• Bacteria


  Prokaryotes that have peptidoglycan in their cell walls
• Archaea


  Prokaryotes that DO NOT have peptidoglycan in their cell walls, live in extreme environments, have DNA sequence different from bacteria and eukaryotes
• Three groups of Archaea

  • Methanogens
  • Extreme Halophiles
  • Hyperthermophiles
• The four kingdoms of Eukaryotes

  • Plants
  • Animals
  • Fungi
  • Protists
• The hierarchy for classifying Eukaryotes is Domain -> Kingdom -> Phylum -> Class -> Orders -> Families -> Genera -> Species

  
• The hierarchy for classifying Prokaryotes is Domain -> Phylum -> Class -> Orders -> Families -> Genera -> Species

  
• Taxonomy is still an evolving discipline, with systems of classification that change over the years as new information is discovered
• The classification scheme currently favored by most microbiologists is the three-domain system based on rRNA sequence data

  
• Scientific nomenclature (names)


  Every organism is assigned two names, one genus name and one specific name, in a binomial nomenclature (Latin names) so all scientists around the world will understand each other
• After the first use, scientific names can be shortened with the first letter of the genus and the 'specific epithet'
• Humans are Homo sapiens meaning Man and wise