Microbiology Chap 4 Flashcards
Prokaryote characteristics
One circular chromosome not in membrane
No histones or membrane enclosed organelles
Peptidoglycan cell walls if Bacteria & pseudomurein cell walls if Archaea
Divide by binary fission
Eukaryote
Paired chromosomes, in nuclear membrane
Have histones & membrane enclosed organelles
Polysaccharide cell walls
Cell division by mitosis
Prokaryotes cell shape
Most bacteria are monomorphic (one shape); few are pleomorphic (many shapes)
- Bacillus (rod-shaped)
- Coccus (spherical)
- Spiral
Cocci
Can be round, oval, elongated or flattened on one side
Can be found in
Pairs: diplococci
Chains: streptococci
Scientific name: Bacillus
Shape: Bacillus
Can be single, pairs (diplobacilli), chain (streptobacilli) or oval-like (coccobacillus)
Spirals
- Have one or more twists & are never straight
- Vibrio: curved rod
- Spirillum: helical shape like corkscrew; have rigid bodies
- Spirochete: helical shape & flexible bodies
Prokaryotes structures External to Cell Wall
- Glycocalyx
- flagella
- axial filaments
- fimbriae
- pili
Glycocalyx
Sticky layer of polysaccharides outside of cell wall
Two types of Glycocalyx
Capsule: neatly organized and firmly attached
Slime layer: unorganized & loose
Capsules attribute to virulence by
Allowing cell to attach
Preventing phagocytosis
Atrichous
no flagella
Peritrichous
flagella all over the cell
Polar:
flagella on 1 side
Monotrichous:
1 flagellum
Amphitrichous
flagella on both sides
Lophotrichous
tuft of flagella coming from 1 side
Chemotaxis
chemical
Phototaxis
light
Flagella proteins
are H antigens distinguish among serovars
EXAM
Axial Filaments
- Also called endoflagella; found in spirochetes
- Bundles of fibrils that arise at end of cell beneath outer sheath, spiral around; anchored at one end of cell
Axial filament rotation
Rotation causes cell to move like corkscrew
protein pilin
is arranged in helical structure
Fimbriae
: hairlike appendages that allow for attachment
Pili
- Involved in motitly & DNA transfer between cells
- Gliding motility: smooth gliding movement
- Twitching motility: pilus extends by addition of more pilin, makes contact & retracts as disassembled
- Conjunction (sex) pilus: F+ cells connects to receptors on another cell & DNA from F+ cell is transferred
Cell Wall
Prevents lysis when water pressure inside cell is greater then outside
Helps maintain shape, anchor flagella & contributes to virulence
Gram-positive Cell Walls
- Thick peptidoglycan
- Teichoic acids (2 types)
- Lipoteichoic acid links to plasma membrane
- Wall teichoic acid links to peptidoglycan
- May regulate movement of cations & attribute to antigen specificity
- Polysaccharides & teichoic acids provide antigenic specificity
Gram-Negative Cell Wall
- Thin peptidoglycan (bonded to lipoproteins) & outer membrane
- Periplasmic space filled with periplasm (gel-like fluid); high concentration of degradative enzymes & transport proteins
- More prone to mechanical breakage; sensitive to tetracycline
Gram-Negative Cell Wall stuff
Outer membrane: consists of lipopolysaccharides (LPS), lipoproteins & phospholipids; protection from phagocytes, complement (lysing cells & phagocytosis) & antibiotics
LPS consists of
O polysaccharide antigen: useful in identifying gram-negative, ex. E. coli O157:H7
Core polysaccharide: provides stability
Lipid A is endotoxin; causes fever, dilation of blood vessels, shock & blood clotting
Gram-stain
Crystal violet-iodine crystals form in cell, which are too large to leave
Gram-positive (alcohol)
Alcohol dehydrates peptidoglycan making it more impermeable & CV-I crystals do not leave
Gram-negative (alcohol)
Alcohol dissolves outer membrane & leaves holes in peptidoglycan letting CV-I wash out
Safranin dyes
both pink but only visible in Gram-negative
Gram-positive cell walls
- 2-rings in basal body of flagella
- Produce exotoxins
- High susceptibility to penicillin
- Disrupted by lysozyme
Gram-negative cell walls
- 4-rings in basal body of flagella
- Produce endotoxins & exotoxins
- Low susceptibility to penicillin
Acid-fast cell walls
Like gram-positive Waxy lipid (mycolic acid) bound to peptidoglycan
Mycoplasmas
- Lack cell walls
- Sterols in plasma membrane
Archaea
Wall-less or walls of pseudomurein (lack NAM & D-amino acids)
Cell envelope layers
Outer membrane
Cell wall
Plasma membrane
Cell envelope
-Gram-negative All 3 -Gram-positive -Missing the outer membrane -Mycoplasma Only have the plasma membrane
Damage to Cell Wall
- Lysozyme digests disaccharide in peptidoglycan
- Found in sweat, tears & saliva
- Penicillin inhibits peptide bridges in peptidoglycan
- Protoplast is wall-less cell
- Spheroplast is wall-less gram-positive cell
- Protoplasts & spheroplasts are susceptible to osmotic lysis
- L forms are wall-less cells that swell into irregular shapes
