Chap 27

• Characteristics of Prokaryotes

  Unicellularity (Most are single-celled)

  Cell size (Most are less than 1 μm in diameter)

  Nucleoid (Chromosome is single circular double-stranded DNA)

  Cell division (Most divide by binary fission)
• Prokaryotes fall into two domains: Bacteria and Archaea.
• Characteristics of Prokaryotes

  Genetic recombination (Exchange genetic material extensively through horizontal gene transfer; not a form of reproduction)

  Internal compartmentalization (No membrane-bounded organelles)

  Flagella (Simple in structure.)

  Metabolic diversity(Oxygenic and anoxygenic photosynthesis)
• Bacteria and archaea differ in four key areas:

  1. Plasma membranes (Prokaryotes have one)
  2. Cell walls (All prokaryotes have cell walls but Bacteria have peptidoglycan)
  3. DNA replication
  4. Gene expression
• Bacteria vs. Archaea

  Cell wall - Bacteria have peptidoglycan but Archaea lack peptidoglycan.

  DNA replication - Both have single replication origin but nature of origin and proteins used are different. Archaeal DNA replication is more similar to that of eukaryotes.

  Gene Expression - Archaeal transcription and translation are more similar to those of eukaryotes
• Prokaryotic Cell Structure 3 basic shapes

  1. Bacillus-Rod-shaped.

  2. Coccus-Spherical.

  3. Spirillum-Helical-shape
• Endospores will develop a thick wall around their genome and some of the cytoplasm when exposed to environmental stress.
• Prokaryotic cell walls

  Gram positive bacteria - Thick, complex network of peptidoglycan and contains lipoteichoic and teichoic acid.

  
  

  Gram negative bacteria • Thin layer of peptidoglycan, Second outer membrane with lipopolysaccharide and Resistant to many antibiotics

  
  

  S-layer - Rigid paracrystalline layer found in some bacteria and archaea. Outside of peptidoglycan or outer membrane layers in gram-negative and gram-positive bacteria. Diverse functions – often involves adhesion.

  
  

  Capsule - Gelatinous layer found in some bacteria. Aids in attachment. Protects from the immune system.
• Prokaryotic cell organization

  Nucleoid region - Contains the single, circular chromosome and contain plasmids.

  Ribosomes - Smaller than those of eukaryotes, Differ in protein and RNA content and Targeted by some antibiotics.
• Prokaryotes do not reproduce sexually 3 types of horizontal gene transfer

  Transformation —from the environment.

  Transduction —by viruses.

  Conjugation —cell to cell contact.
• Transformation

  Natural transformation - DNA that is released from a dead cell is picked up by another live cell

  Artificial transformation - Some species do not naturally undergo transformation so it's accomplished in the lab
• Transduction

  Generalized transduction - Virtually any gene can be transferred.

  Specialized transduction - Imprecise excision of prophage DNA.
• Conjugation

  Plasmids may encode functions not necessary to the organism, but may provide a selective advantage.
• F plasmid transfer F + cell produces F pilus that connects it to F− cell. Transfer of F plasmid occurs through conjugation bridge F plasmid copied through rolling circle replication. The end result is two F+ cells
• Prokaryotic Metabolism

  Acquisition of carbon

  
  

  Autotrophs – from inorganic CO2

  Photoautotrophs – energy from Sun.

  Chemolithoautotrophs – energy from oxidizing inorganic substances

  
  

  Heterotrophs – from organic molecules.

  Photoheterotrophs – light as energy source but obtain organic carbon made by other organisms.

  Chemoheterotroph – both carbon atoms and energy from organic molecules.
• Bacteria are used for bioremediation

  Remove pollutants from water, air, and soil.

  Biostimulation – adds nutrients to encourage growth of naturally occurring microbes

  Halorespiration – bacteria remove halogenated compounds from toxic waste.
• Syphilis has four distinct stages

  1. Chancre – highly infectious

  2. Rash – infectious

  3. Latency – no longer infectious but attacking internal organs

  4. Damage now evident – heart disease, mental deficiency, nerve damage
• Early Classification Characteristics

  1. Photosynthetic or non-photosynthetic
  2. Motile or non-motile
  3. Unicellular, colony-forming, or filamentous
  4. Formation of spores or division by transverse binary fission
  5. Importance as human pathogens or not.
• Prokaryote Molecular Classification

  1. Amino acid sequences of key proteins

  2. Percent guanine–cytosine content

  3. Nucleic acid hybridization

  4. Gene and RNA sequencing

  5. Whole-genome sequencing
• A bacteriophage is a virus that infects a bacterium.
• Phages are usually extremely host specific and can only infect a single bacterial species.
• Bacteria that form spores are capable of survival under adverse environmental conditions.
• In 1982, researchers discovered that a major cause of human ulcers was due to infection with the following bacterium Helicobacter pylori.
• Tetraethers are more thermally stable.
• When bacteria take up DNA from the environment, it is called transformation.
• A process known as transduction involves viruses as a means of bacterial DNA exchange.
• Many bacteria exchange genetic material through a mating process called conjugation.
• A special kind of pilus called a conjugation bridge allows transfer of the F plasmid.
• Recipient cells become donor cells after conjugation because they have received genes that allow them to produce a sex pilus.
• Proteins released by bacterial pathogens in humans help avoid the immune system and invade tissues.
• Bacteria are on a separate branch of the tree of life than Archaea and Eukarya.
• Common in all Prokaryotes - Nucleoid, Binary Fission, and circular chromosome.

  Uncommon in all Prokaryotes - Endospores, Capsules, Flagella's, S Layer and cell wall.