Lecture 2 Flashcards
Properties of Prokaryotic Bacterial cells
- unicellular
- lacks a membrane-bound nucleus and membrane-bound organelles
- multiply by binary fission
Major cell morphologies
Coccus- spherical
Strepto/Staphylo- ovoid
Rod/Bacillus- cylindrical
Spirilla- spiral
Pleomorphic
Assuming several different shapes
Hypha and Stalk functions
Hypha- indicates directionality of growth
Stalk- straw for nutrients
Coccus naming
diplococci (2) streptococci (line) tetrads (4) sarcinae (2x2 box) staphylococci (grape bundle)
Bacillus naming
bacillus diplobacilli (2) streptobacilli (line) palisade (group) v-shape
Cytoplasmic membrane
- thin structure that surrounds the cell found in all life forms
- separates cytoplasm from environment
- highly selective permeability
Functions of the cytoplasmic membrane
Permeability barrier- prevents leakage and functions as a gateway for transport of nutrients into and out of the cell
Protein Anchor- site of many proteins involved in transport, bioenergetics, and chemotaxis
Energy Conservation- stie of generation and use of the proton motive force
Peptidoglycan
rigid layer that provides strength to cell wall
- composed of G and M sugars linked by peptide bridges
- Lysine or DAP
Bacterial cell wall
- semi-rigid structure for cell shape
- protects cell from rupture (osmotic stress)
- composed of peptidoglycan (PG)
Gram positive cell wall
- G and M sugars
- peptide bonds
- glycosidic bonds
- interbridge (Gly) between the peptide bridge
Gram negative cell wall
- G and M sugars
- peptide bonds
- glycosidic bonds
Glycan tetrapeptide
Fundamental unit of peptidoglycan
- G and M sugars
- B(1, 4) bond
- L-alanine
- D-glutamic acid
- DAP
- D-alanine
Gram-positive cell walls
- up to 90% peptidoglycan
- very thin periplasmic space
- common to have teichoic acids
Teichoic acid
Negatively charged acidic substances that attracts Na+, Ca2+, Mg2+ embedded in the cell wall
- Lipoteichoic: covalently bound to membrane lipids (into the lipid bilayer
- provide rigidity to the cell-wall
- play a role in biofilm formation
Gram-negative outer membrane
- 10% peptidoglycan
- most of cell wall composed of LPS layer
- porins
- periplasm
LPS
Lipopolysaccharide
- functions as protection (very hard layer)
- lipid A (lodges into outer membrane)
- core polysaccharide
- O-polysaccharide (allows for subtyping)
Endotoxin
Toxic component of LPS (lipid A)
2 ways of release into the bloodstream:
- bacterial replication (lipid A falls out)
- bacterial death (lipid A is liberated)
Porins
channels for movement of hydrophilic low molecular-weight substances
Periplasm
space located between cytoplasmic and outer membrane
- houses many proteins, especially ones involved w/ transportation of nutrients and structures
Capsules and Slime layers
- polysaccharide layers
- assist in attachment to surfaces
- aid in evasion of immune system
- resist desiccation
Fimbriae
filamentous protein structures
- enable organisms to stick to surfaces or form pellicles
Pilli
filamentous protein structure
- typically longer than fimbriae
- assist in surface attachment
- facilitate genetic exchange between cells (may increase survivability)
- type IV involved in twitching motility
Gram Stain procedure
Developed by Hans Gram in 1844
- Bacterial suspension air dried on glass slide
- crystal violet stain for 1 minute
- Iodine for 1 minute- forms a complex with crystal violet which sticks into the PG layer
- 05% alcohol or acetone for 10 seconds- dehydrates/dissolves the lipid membrane
- Safranin 30 seconds- works as a counterstain, must be a different colour than crystal violet
Gram-positive cell
crystal violet stays in cell and is sealed by the ethanol
- wall is too thick to allow uptake of decolourizing agent and remains violet
Gram-negative cell
10% peptidoglycan layer allows the crystal violet to escape
- lipid layer is dissolved
- de-colurizer diffuses through cell-wall and decolourizes crystal violet
What is the essence of gram stain?
The ability of bacteria to retain the crystal dye
G+ examples
- mostly cocci
- some bacilli
G- examples
- mostly bacilli
- some cocci
