Motility Flashcards
What are external structures?
- extend beyond the cell envelope in bacteria and archaeons
- function in protection, attachment to surfaces, horizontal gene transfer, and cell movement
- ex: fimbriae, pili, and flagella
What is are sex pili?
- similar to fimbriae except longer, thicker, and less numerous (1-10/cell)
- genes for formation are found on a plasmid (called fertility plasmid)
- required for conjugation
- one bacteria sends the fertility plasmid to another bacteria via the sex pilus
What are fimbriae and pili?
- short, thin, hair-like proteinaceous appendages (up to 1,000 per cell)
- mediate attachment to surfaces
- some (type IV pili) required for motility or DNA uptake
How are sex pili seen under the microscope?
- use a virus as a mordant
- makes the pilus appear thicker so it can be viewed under the microscope
What are flagella?
- thread-like appendages extending outward from the plasma membrane and cell wall
- functions in motility and swarming behavior and attachment to surfaces
- may be a virulence factor because the flagella allows the bacteria to burrow themselves into tissues
monotrichous
one flagellum
polar flagellum
flagellum/flagella at the end of the cell
amphitricous
one flagellum at each end of the cell
lophotricous
cluster of flagella at one or both ends
peritrichous
flagella spread over entire surface of cell
What are the three parts of the flagella?
- filament
- hook
- basal body (motor)
What provides the energy for rotation of the flagellum?
proton motive force
What is the mechanism of flagellar movement?
- the flagellum is a motor that produces torque
- the rotor is a C ring and an MS ring that turn and interact with the stator
- the stator is made of Mot A and Mot B proteins that H+ ions flow through in order to move the C and MS rings
What is the biosynthesis of the flagella?
- MS/C ring
- Mot proteins
- P ring
- L ring
- early hook
- late hook (with cap)
- filament and hook-filament junction
How does the filament grow?
from tip to base
What is the difference between gram positive and gram negative flagella?
- gram negative flagella have 4 rings (L,P,MS, and C)
- gram positive flagella have 2 rings (MS and C)
- L and P ring offer stability to gram negative bacteria that have a thin layer of peptidoglycan
What happens when the flagella rotates counterclockwise?
forward motion (run)
What happens when the flagella rotates clockwise?
- disrupts run causing cell to stop and tumble
- tumbles allow the cell to change direction (but the new direction is random)
How do spirochetes move?
- spirochetes have multiple flagella (endoflagella) that form an axial fibril that winds around the cell
- the flagella remain in the periplasmic space inside the outer sheath
- exhibits flexing and spinning movements
- good for pathogens because they can burrow into tissues
What is twitching motility?
- pili at the ends of cell
- short, intermittent, jerky motions
- cells are in contact with each other and the surface
What is gliding motility?
- smooth movements
- often involves slime
- usually social
- glide proteins pull the bacteria forward
What is chemotaxis?
- movement toward a chemical attractant or away from a chemical repellant
- concentrations of chemoattractants and chemorepellants detected by chemoreceptors on surfaces of cells
- complex but rapid
- responses occur in less than 20 milliseconds
- 2-over 60 cell lengths/sec
What is positive chemotaxis?
- going toward an attractant
- runs are longer
- tumbles are less frequent
What is negative chemotaxis?
- going toward a repellant (trying to move away)
- runs are shorter
- tumbles are more frequent
