Bacteria and Archea

• Prokaryotes thrive almost everywhere, including places too acidic, salty, cold, or hot for most other organisms.
• • Prokaryotes are divided into two domains

  Bacteria and Archea
• • Most prokaryotes are unicellular, although some species form colonies.
• • Prokaryotic cells three most common shapes are

  spheres (cocci), rods (bacilli), and spirals.
• • An important feature of nearly all prokaryotic cells is their cell wall, which maintains cell shape, provides physical protection, and prevents the cell from bursting in a hypotonic environment.
• • Eukaryote cell walls are made of cellulose or chitin.
• • Bacterial cell walls contain peptidoglycan, a network of sugar polymers cross-linked by polypeptides.
• • Gram-negative bacteria have less peptidoglycan and an outer membrane that can be toxic, and they are more likely to be antibiotic resistant.
• How does antibiotics work?

  Many antibiotics target peptidoglycan and damage bacterial cell walls... (often causing cell lysis).
• • A polysaccharide or protein layer called a capsule covers many prokaryotes.
• • Some prokaryotes have fimbriae (also called attachment pili), which allow them to stick to their substrate or other individuals in a colony
• Sex pili are longer than fimbriae and allow prokaryotes to exchange DNA by conjugation.
• • Most motile bacteria propel themselves by flagella that are structurally and functionally different from eukaryotic flagella.
• Many bacteria exhibit taxis, the ability to move toward or away from certain stimuli.
• • Prokaryotic cells usually lack complex compartmentalization.
• • Most of the genome consists of a circular chromosome.
• • Some species of bacteria also have smaller rings of DNA called plasmids.
• • The typical prokaryotic genome is a ring of DNA that is not surrounded by a membrane and that is located in a nucleoid region.
• Prokaryotes reproduce asexually quickly by binary fission and can clone / divide every 1–3 hours.
• Endospores are adaptation to survive dormant in harsh environment
• Three factors contribute to this genetic diversity:

  Rapid Reproduction, Mutation, Genetic Recombination
• • Mutation rates during binary fission are low, but because of rapid reproduction, mutations can accumulate rapidly in a population.
• • High diversity from mutations allows for rapid evolution.
• • A prokaryotic cell can take up and incorporate foreign DNA from the surrounding environment in a process called transformation.
• • Transduction is the movement of genes between bacteria by bacteriophages
• viruses that infect bacteria

  Bacteriophage
• • Conjugation is the process where genetic material is transferred between bacterial cells.
• • Sex pili allow cells to connect and pull together for DNA transfer.
• • A piece of DNA called the F factor is required for the production of sex pili.
• R plasmids carry genes for antibiotic resistance.
• metabolic adaptations

  Autotroph, Heterotrophs
• • Phototrophs obtain energy from light
• Chemotrophs obtain energy from chemicals.
• • Autotrophs require CO2 as a carbonsource.
• • Heterotrophs require an organic nutrientto make organic compounds.
• four major modes of nutrition

  Photoautotrophy, Chemoautotrophy, Photoheterotrophy, Chemoheterotrophy
• Obligate aerobes require O2 for cellular

  respiration.
• Obligate anaerobes are poisoned by O2 and use fermentation or anaerobic respiration.
• Facultative anaerobes can survive with or without O2.
• • In nitrogen fixation, some prokaryotes convert atmospheric nitrogen (N2) to ammonia (NH3).