Exam 2 Bacterial Structures 10/5 Flashcards
How can bacteria avoid antibiotic treatment
Find a way for bacteria to go into dormancy
Producing more enzyme so that the antibiotic cant keep up inhibiting the enzymes at a rate that slows or stops their work
Beta-lactam antibiotic resistance
Efflux pumps
Mutations in pore proteins
Beta lactamases
The cell envelope:
Gram-positive cells
-Thick outer layer of peptidoglycan
-Very narrow periplasmic space
-Teichoic acids in the peptidoglycan
The cell envelope:
Gram-negative cells
-A varying width periplasmic space
-Very thin layer of peptidoglycan
-An outer membrane composed of Lipopolysaccharide (LPS)
LPS
Lipid A
Core polysaccharide
O-antigen
Importance of LPS
contributes to negative charge on cell surface
helps stabilize outer membrane structure
may contribute to attachment to surfaces and biofilm formation
creates a permeability barrier
protection from host defenses
can act as an endotoxin
Porin Proteins in E. coli
more permeable than plasma membrane due to presence of porin proteins and transporter proteins
The cell wall:
Gram-positive
peptidoglycan layer has large pores throughout its matrix.
The cell wall:
Gram-negative
cell has
porin and TonB proteins in its
outer membrane to transfer
molecules into the periplasmic
space.
The cell envelope:
Some move from the periplasm to outside directly (these are known as autotransporters and are rare).
Some use single-step (never entering the periplasm) transport systems.
The bacterial cell surface:
Motility from flagella: spiral, hollow, rigid filaments extending from the cell surface
Locations and number vary from species to species.
Patterns of Flagella Distribution
*know for exam
monotrichous – one flagellum
polar flagellum – flagellum at end of cell
amphitrichous – one flagellum at each end of cell
lophotrichous – cluster of flagella at one or both ends
peritrichous – spread over entire surface of cell
Three Parts of Bacterial Flagella
Motility from flagella
Composed of three basic pieces:
-Filament
-Hook protein
-Basal body
Bacterial Flagellar Movement
flagellum rotates like a propeller
very rapid rotation up to
1100 revolutions/sec
counterclockwise (CCW) rotation causes forward motion (run)
clockwise rotation (CW) disrupts run causing cell to stop and tumble
Chemotaxis
movement toward a chemical attractant or away from a chemical repellent
changing concentrations of chemical attractants and chemical repellents bind chemoreceptors of chemosensing system
Motility by flagella
By using chemoreceptor proteins to sense changes in concentrations of attractants or repellents, cells can produce more runs to move in a particular direction.
Mechanism of Flagellar Movement
flagellum is 2 part motor producing torque
rotor
- C (FliG protein) ring and MS ring turn and interact with stator
stator (electromagnet)- Mot A and Mot B proteins
Archaea-have a push me-pull me alternation with no tumbles
The bacterial cell surface:
Motility from flagella
- Not all cells have EXTERNAL flagella!
- Some spirochetes have flagella in the periplasm.
The bacterial cell surface:
Nonflagellar motility
- Gliding motility: smooth sliding over a surface
(myxobacteria, cyanobacteria) - Twitching motility: slow, jerky process using (pili) (N.meningitidis, P. aeruginosa)
The bacterial cell surface:
Polymerization of actin-for propulsion of bacteria into adjacent cells (Shigella dysenteriae, Listeria monocytogenes)
Adherence molecules to stick to surfaces
Cell surface
- Mediated by pili, fibers of pilin protein possess other proteins on their tips for sticking.
- A sex pilus is a different structure used for conjugation.
- Some scientists prefer to use “pili” only for conjugation structures and “fimbriae” (s. fimbria) for adherence.
- Some microbes (Caulobacter, Hyphomonas) use an extension of the cell envelope tipped by a “holdfast” of polysaccharides.
Components Outside of the Cell Wall
outermost layer in the cell envelope
glycocalyx
- capsules and slime layers
- aid in attachment to solid surfaces
- e.g., biofilms in plants and animals
S-layers
Capsules
composed of polysaccharides
well organized and not easily removed from cell
visible in light
microscope
protective
advantages
