Topic 4 - Prokaryotic Cell Morphology Part 2 Flashcards
Functions of external structures in bacteria and archaea
- Protection
- Attachment to surfaces
- Horizontal gene transfer
- Cell movement
Some structures that extend beyond the cell envelope in bacteria and archaea
- Fimbriae
- Pili
- Flagella
Short, thin, hairlike, proteinaceous appendages (up to 1,000/cell)
Fimbriae (s. fimbria)
What is the job of fimbriae?
- Mediate attachment to surfaces
- Some (type IV fimbriae) required for motility or DNA uptake)
- Longer, thicker, and less numerous then fimbriae
Sex pili (pl, pilus)
Functions of sex pili
- Genes for formation found on plasmids
- Required for conjugation
Threadlike, locomotor appendages extending outward from plasma membrane and cell wall
Flagella
Functions of flagella
- Motility and swarming behavior
- Attachment to surfaces
- May be virulence factors
- Thin, rigid protein structures that cannot be observed with bright-field microscope unless specially stained
- Pattern of flagellation varies
Domain Bacteria flagella
One flagellum
Monotrichous
Flagellum at end of cell
Polar flagellum
One flagellum at each end of cell
Amphitrichous
Cluster of flagella at one or both ends
Lopchotrichous
Flagella spread over entire surface of cell
Peritrichous
Three parts of a flagellum
- Filament
- Hook
- Basal body
- Extends from surface to the tip of flagellum
- Hollow, rigid cylinder
- Composed of the protein flagellin
- Some bacteria have a sheath around filament
Filament
The protein that composes the flagellum filament
Flagellin
- In the flagellum
- Links filament to basal body; made of protein
Hook
- Series of rings that drive flagellar motor
Basal body
Explain flagellar synthesis
- Complex process involving many genes and proteins
- New flagellin molecules transported through the hollow filament to tip
- Filament subunits self-assemble with help of filament cap at tip, not base
Motility in domain Bacteria and Archaea
- Flagellar movement
- Spirochete motility
- Twitching motility
- Gliding motility
Directed cell movement in response to some stimulus
Taxis
Move toward chemical attractants such as nutrients, away from harmful substances
Chemotaxis
Bacteria and Archaea can also move in response to what?
Temperature, light, oxygen, osmotic pressure, and gravity
Changing concentrations of chemical attractants and chemical repellents does what?
Binds chemoreceptors of chemosensing system
- Flagellum rotates like a propeller
- Very rapid rotation up to 1100 revolutions/sec
Bacterial flagellar movement