MICB Lecture 2

• Domain Bacteria

  Features

  • habitat: terrestrial and aquatic
  • reproduction: asexual (binary fission)
  • size: 0.3um-100um
• Provide genus name

  Genus: Thiomargarita

  one of the largest bacteria, >100um

  
• Coccus shaped cells

  Coccus: spherical

  • diplococcus: pairs
  • streptococcus: chains (twisted)
  • staphylococcus: grape-like clusters
  • tetrads: 4 cocci in one square
• Bacillus shaped cells

  Bacillus: rod

  • vibrio: curved rod
• Helical shapes

  spirillum: rigid helix

  • spirochete: flexible helix
• Pleomorphic shape

  variable
• Hyphae


  long filaments that some bacteria and many fungi form
• mycelium


  network of hyphae
• Shape of bacteria

  Grape-like clusters

  A) coccus- staphylococcus

  
• Shape of bacteria

  Rod

  A) Bacillus

  
• Shape of bacteria

  rigid helix

  A) spirillum

  
• Shape of bacteria

  chains (twisted)

  A) streptococcus

  
• Shape of bacteria

  curved rod

  A) vibrio

  
• shape of bacteria/ name

  flexible helix - Borella burgdoferi

  A) spirochete

  
• Shape of bacteria/ genus/ key feature

  genus: Mycoplasma

  key feature: plasma membrane but NO cell wall

  A) bacillus cells

  
• advantages to being small

  Advantages:

  • More efficient uptake of nutrients
  • faster growth
  • smaller cells have higher surface:volume ratio (rod has higher SV than coccus)
• Bacterial cell organization STRUCTURES

  cell envelope

  cytoplasm

  external structures
• Bacterial cell envelopeSTRUCTURES

  plasma membrane

  cell wall (outside of plasma membrane)

  layers outside of cell wall
• plasma membrane/cytoplasmic membrane

  innermost layer

  • selectively permeable barrier
  • main site of energy generation (via electron transport chains)
  • transport systems (bring nutrients in)
  • signal transduction system (sense and respond to environment)
• selectively permeable barrier

  allow particle molecules to pass in and out of cell, while preventing others
• Model name

  Structure of a phospholipid

  • lipid bilayer in which proteins float
  • flexible ester bonds
  • amphipathic

  A) hydrophilic

  B) hydrophobic tails

  
• amphipathic 


  polar ends are hydrophilic (like water), nonpolar tails are hydrophobic
• Structure of what

  Bacterial membrane

  A) phospholipid

  
• Bacterial cell wallFUNCTIONS

  Functions:

  • protection: toxic substances, osmotic lysis
  • bacteria often in hypotonic solutions
  • [solute] outside cell< [solutle] inside cell
  • rigid, compared to plasma membrane
• osmosis

  movement of water from lower to higher concentration (moves outward)
• Gram stain procedure

  gram positive stain purple

  gram negative stain pink

  color change is due to difference in cell walls
• Peptidoglycan

  Important component of cell wall in gram positive and negative bacteria

  • polysaccharide formed from alternating sugar subunits (NAM and NAG)
  • sugar chains cross-linked by peptides of alternating D and L amino acids
  • strand is helical
• Picture of..

  Peptidoglycan

  • 1,4 Bond - lysozyme enzyme can cut

  A) beta 1,4 glycosidic bond

  B) peptide

  
• transpeptidation

  rxn forming cross links, peptides are strong because of this
• Cross-links

  Direct: connecting carboxyl group of amino acid in one stem to amino group of an amino acid in another

  Indirect: short chain of amino acids linking the stem peptide of one peptidoglycan to another (uses peptide interbridges)

  • Gram positive tend to have more cross linking than gram negative

  A) direct

  B) indirect

  
• Which cell wall:

  Gram positive

  • thick peptidoglycan layer
  • small periplasmic space

  A) gram positive

  B) peptidoglycan

  C) plasma membrane

  D) cell wall

  E) Cytoplasm

  
• Which cell wall

  Gram negative

  • thin layer of peptidoglycan
  • large periplasmic space

  A) gram-negative

  B) cell wall

  C) outer membrane

  D) peptidoglycan

  E) plasma membrane

  F) periplasmic space

  G) cytoplasm

  
• Gram-positive cell walls

  Primary peptidoglycan

  • teichoic acids: polymers of glycerol or ribotol that provide stability
  • most bacteria belong to 2 phyla: firmicutes and actinobacteria
  • lipoteichoic acids: covalently connected to plasma membrane

  A) lipoteichoic acid

  B) teichoic acid

  C) cell wall

  D) peptidoglycan

  E) periplasmic space

  F) plasma membrane

  
• Gram negative cell walls

  Thin peptidoglycan surrounded by outer membrane of lipids, proteins and lipopolysaccharide (LPS)

  • no teichoic acids
  • porins: channels in outer membrane

  A) LPS

  B) porin

  C) peptidoglycan

  D) cell wall

  E) outer membrane

  F) plasma membrane

  
• LPS consists of

  O side chain, core polysaccharide, lipid A
• lipid A

  contains 2 glucosamine sugar derivatives, each with a fatty acid and phosphate attached
• core polysaccharide

  joined to lipid A and is constructed of 10 sugars
• O antigen

  polysaccharide chain extending outward from the core, can vary in composition between bacterial strains
• Importance of LPS

  Protection for host defenses

  O antigens vary, Escherichia coli: O157:H7

  Attachment

  Stability (outer membrane in particular)

  Lipid A can act as toxin

  endotoxin (fever, septic shock)
• Lysis

  burst of cell, without peptidoglycan layer of cell wall, pressure on plasma membrane would burst