Eukaryotes

• Bacteria and Archaea

  are the two main

  branches of

  prokaryotic evolution
• Three common shapes of bacteria:

  cocci

  bacilli

  spirochete
• cocci – spherical cells
• Streptococci – cocci in chains
• Staphylococci – cocci in clusters
• bacilli – rod shaped prokaryotes
• External Features of Prokaryotes:

  • Cell Shape
  • Cell Wall
  • Capsule
  • Projections
• Cell Wall ▫ Most (but not all) prokaryotic cells

  have a cell wall, but the makeup of this

  cell wall varies
• The composition of the cell wall differs

  significantly between the domains

  Bacteria and Archaea.
• eukaryotic cell walls

  found in plants (cellulose)
• eukaryotic cell walls

  found in fungi and

  insects (chitin).
• Cell Wall: Function

  The cytoplasm of prokaryotic cells has a high concentration of

  dissolved solutes. Therefore, the osmotic pressure within the cell is

  relatively high.
• high concentration of dissolved solute is directly proportional to the osmotic pressure within the cell
• Cell Wall: Function

  The cell wall provides physical protection and prevents the cell

  from bursting in a hypotonic environment
• Bacterial cell walls contain peptidoglycan composed of polysaccharide

  chains that are cross-linked by unusual peptides
• Bacteria are divided into two major groups: gram-positive and gram-

  negative, based on their reaction to gram staining
• Both groups have a cell wall composed of

  peptidoglycan: in gram-positive bacteria,

  the wall is thick, whereas in gram-negative

  bacteria, the wall is thin.
• In gram-negative bacteria, the cell wall is

  surrounded by an outer membrane that

  contains lipopolysaccharides and

  lipoproteins.
• In medicine, Gram stains are often used to detect

  the presence of bacteria and indicate the type of

  antibiotic to prescribe.
• Capsule

  ▫ Outside the cell wall
• The capsule found in some species

  enables the organism to attach to

  surfaces, protects it from dehydration

  and attack by phagocytic cells, and

  increases its resistance to our immune

  responses
• The capsule surrounding the

  Streptococcus bacterium enables it to

  attach to cells that line the

  human respiratory tract—a tonsil cell.
• Some prokaryotes have flagella

  (singular, flagellum) used for

  locomotion
• a prokaryote can

  move toward nutrients or other

  members of its species or away

  from a toxic substance, because of it's flagella
• Flagella may be scattered over

  the entire cell surface or

  concentrated at one or both ends

  of the cell.
• Unlike the flagellum of eukaryotic

  cells the prokaryotic flagellum is a

  naked protein structure that lacks

  microtubules.
• Fimbriae

  ▫ Hairlike projections that enable

  some prokaryotes to stick to a

  surface or to one another -

  attachment
• Fimbriae allow many pathogenic

  bacteria to latch onto the host cells

  they colonize.
• Neisseria gonorrhoeae, which causes the sexually

  transmitted infection gonorrhea, uses fimbriae to attach to

  cells in the reproductive tract.
• Prokaryotic cells do not have

  chloroplasts, but some prokaryotes

  have thylakoid membranes where

  photosynthesis takes place
• Photoheterotrophs obtain energy from sunlight but get

  their carbon atoms from organic

  sources
• Because they don’t depend on

  sunlight, chemoautotrophs can

  thrive in conditions that seem

  totally inhospitable to life (ex.

  Hydrothermal vents
• CHEMOHETEROTROPHS by far the largest and most diverse

  group of prokaryotes. Almost any

  organic molecule is food for some

  species of chemoheterotrophic

  prokaryote
• Reproduction in prokaryotes is

  asexual and usually takes place by

  binary fission.
• Binary fission does not provide an opportunity for genetic

  recombination or genetic diversity, but prokaryotes can share

  genes by three other mechanisms:

  1. Transformation
  2. Tranduction
  3. Conjugation
• prokaryote takes in DNA found in its environment that is shed by other prokaryotes, alive or dead

  Transformation
• If a nonpathogenic bacterium takes up

  DNA for a toxin gene from a pathogen

  and incorporates the new DNA into its

  own chromosome, it, too, may become

  pathogenic.
• Transduction

  results in a recombinant organism.
• In transduction, bacteriophages

  sometimes also move short pieces of

  chromosomal DNA from one

  bacterium to another.
• bacteriophages -the viruses that infect bacteria