prokaryotes

• Prokaryotes


  Bacteria and Archaea
• Describe common features of prokaryotes that make them so successful
• Understand how bacteria are important for other organisms, including humans
• Prokaryotes


  • Unicellular
  • Small (0.5–5 µm)
  • Rapid generation time
  • Incredible genetic diversity
  • Horizontal gene transfer
• Cell wall


  Maintains cell shape, protects the cell, mitigate changes in osmotic pressure
• Bacterial cell walls


  Contain peptidoglycan, a network of polysaccharides cross-linked by polypeptides

  
• Archaea cell walls


  Contain polysaccharides and proteins but is structurally different than peptidoglycan
• Taxis


  The ability to move toward or away from a stimulus
• Chemotaxis


  Movement toward or away from a chemical stimulus
• Phototaxis

  Movement toward or away from light
• Prokaryotic cells usually lack compartmentalization
• Some prokaryotes possess specialized membranes for metabolic functions
• Prokaryotic genomes (DNA)


  Consists of a circular chromosome, some bacteria also have plasmids, small circular pieces of DNA
• Binary fission

  Prokaryotes reproduce quickly (~1-3 hours) by this process
• Factors contributing to genetic diversity in prokaryotes

  • Rapid reproduction
  • Mutation
  • Genetic recombination
  • Transformation
  • Transduction
  • Conjugation
• Transformation


  Prokaryotic cell takes up and incorporates foreign DNA from the environment
• Transduction


  Movement of genes between bacteria by bacteriophages (viruses that infect bacteria)
• Conjugation


  Genetic material is transferred between prokaryotic cells, DNA transfer is one way, donor cell attaches to a recipient by a sex pilus, pulls it closer, and transfers DNA
• Prokaryotic metabolism

  • Phototrophs: obtain energy from light
  • Chemotrophs: obtain energy from chemicals and organic molecules
• Prokaryotic carbon sources

  • Autotrophs: require CO2
  • Heterotrophs: require organic nutrients to make organic compounds
• Prokaryotic oxygen requirements

  • Obligate aerobes: require O2
  • Obligate anaerobes: poisoned by O2
  • Facultative anaerobes: can survive with or without O2, but grow best with O2
  • Aerotolerant: can survive with or without O2, and show no difference in growth with or without O2
• Prokaryotic phylogeny is constantly changing
• Archaea


  Many are found in extreme environments and are known as extremophiles, including halophiles, thermophiles, and methanogens
• Bacteria


  Bacteria include the vast majority of prokaryotes of which people are aware, bacterial species are often distinguishable by genomic sequence and morphology, bacterial species concept: genomic and phenotypic consistency
• Bacterial cell wall types

  • Gram-positive: have simpler cell walls with a large amount of peptidoglycan
  • Gram-negative: have less peptidoglycan
• Bacterial shapes

  • cocci
  • bacili
  • spirilli

  
• Symbiosis

  Ecological relationship in which two species live in close contact, a larger host and smaller symbiont
• Types of symbiosis

  • Mutualism: both symbiotic organisms benefit
  • Commensalism: one organism benefits while neither harming nor helping the other
  • Parasitism: one organism (the parasite) harms its host
• Many prokaryotes function as decomposers, contributing to chemical recycling within ecosystems
• Cyanobacteria perform photosynthesis in aquatic ecosystems
• Nitrogen fixing bacteria live in symbiosis with plants (root nodules)
• Microbiome in animal guts contains symbiotic prokaryotes
• Prokaryotes cause about half of all human diseases
• Human intestines are home to about 500–1000 species of bacteria, many of which are mutualistic and break down food that is undigested by our intestines
• Bacteria are used as "chemical factories", in bioremediation, and for biofuels