Flagella and Motility
Flagella and Motility
- Most motiles move by use of flagella (flagellum) thread like locomotor appendages extending outward from the plasma membrane and cell wall.
- They are slender, rigid structures, about 20 nm across and up to 15 or 20 pm long.
- Flagella are so thin they cannot be observed directly with a bright-field microscope, but must be stained with special techniques designed to increase their thickness.
- The detailed structure of a flagellum can only be seen in the electron microscope.
- Bacterial species often differ distinctively in their patterns of flagella distribution.
- Monotrichous bacteria (trichous means hair) have one flagellum; if it is located at an end, it is said to be a polar flagellum.
- Amphitrichous bacteria (amphi mean “on both sides”) have a single flagellum at each pole.
- In contrast, lophotrichous bacteria (lopho means tuft) have a cluster of flagella at one or both ends.
- Flagella are spread fairly evenly over the whole surface of peritrichours (peri means “around”) bacteria.
- Flagellation patterns are very useful in identifying bacteria.
Flagellar Ultra structure : –
- Transmission electron microscope studies have shown that the bacterial flagellum is composed of three parts.
- (1) The longest and most obvious portion is the filament, which extends from the cell surface to the tip.
- (2) A basal body is embedded in the cell; and
- (3) a short, curved segment, the hook, links the filament to its basal body and acts as a flexible coupling.
- The filament is a hollow, rigid cylinder constructed of a single protein celled flagellin, which ranges in molecular weight from 30,000 to 60,000.
- The filament ends with a capping protein.
- Some bacteria have sheaths surrounding their flagella.
- For example Vibrio cholerae has a lipopolysaccharide sheath.
- The hook and basal body are quite different from the filament of different protein subunits.
- The basal body is the most complex part of a flagellum.
- In E.coli and most gram-negative bacteria, the body has four rings connected to a central rod.
- The outer L and P rings associate with the lipopolysaccharide and peptidoglycan layers, respectively.
- The inner M ring contacts the plasma membrane.
- Gram-positive bacteria have only two basal body rings, an inner ring connected to the plasma membrane and an outer one probably attached to the peptidoglycan.
Flagellar Synthesis
- The synthesis of flagella is a complex process involving at least 20 to 30 genes.
- Besides the gene for flagellin, 10 or more genes code for hook and basal body proteins ;
- other genes are concerned with the control of flagellar construction or function. It is not known how the cell regulates or determines the exact location of flagella.
The Mechanism of Flagellar Movement
- Procaryotic flagella operate differently from eukaryotic flagella.
- The filament is in the shape of a rigid helix, and the bacterium moves when this helix rotates.
- Considerable evidence shows that flagella act just like propellers on a boat.
- Bacterial mutants with straight flagella or abnormally long hook regions (polyhook mutants) cannot swim.
- When bacteria are tethered to a glass slide using antibodies to filament or hook proteins, the cell body rotates rapidly about the stationary flagellum.
- If polystyrene-latex beads are attached to flagella, the beads spin about the flagellar axis due to flagellar rotation.
- The flagellar motor can rotate very rapidly.
- The E. coli motor rotates 270 revolutions per second ; Vibrio alginolyticus averages 1,100 rps.
- The direction of flagellar rotation determines the nature of bacterial movement.
- Monotrichous, polar flagella rotate slowly clockwise.
- The rotating helical flagellar filament thrusts the cell forward in a run with the flagellum trailing behind.
- Monotrichous bacteria stop and tumble randomly by reversing the direction of flagellar rotation.
- Peritrichously flagellated bacteria operate in a somewhat similar way to move forward, the flagella rotate counterclockwise.
- As they do so, they bend at their hooks to form a rotating bundle that propels them forward.
- Clockwise rotation of the flagella disrupts the bundle and the cell tumbles.
- Because bacteria swim though rotation of their rigid flagella, there must be some sort of motor at the base.
- A rod or shaft extends from the hook and ends in the M ring, which can rotate freely in the plasma membrane.
- It is believed that the S ring is attached to the cell wall in gram positive cells and does not rotate .
- The P and L rings of gram negative bacteria would act as bearings for the rotating rod.
- There is some evidence that the basal body is a passive structure and rotates within a membrane embedded protein.
- The relationship of flagellar rotation to bacterial movement.
- The rotor is like an electrical motor turns in the center of a ring of electromagnets (the stator).
- The exact mechanism that drives basal drives basal body rotation still is not clear provides a more detailed depiction of the basal body in gram negative bacteria.
- The rotor portion of the motor seems to be made primarily of a rod, the M ring, and C ring joined to it on the cytoplasmic side of the basal body.
- These two rings are made of several proteins.
- The two most important proteins in the stator part of the motor are Mot A and Mot B.
- These form a proton channel thought the plasma membrane, and Mot B also anchors the Mot complex to cell wall peptidoglycan.
- There is some evidence that Mot A and G directly interact during flagellar rotation.
- This rotation is driven by proton or sodium gradients in prokaryotes, not directly by ATP as is the case with eukaryotic flagella.
- Bacteria can move by mechanisms other than falgellar rotations.
- Spriochetes are helical bacteria that travel through viscous substances such as mucus or mud by flexing and spinning movements caused by a special axial filament composed of periplasmic flagella.
- A very different type of motility, gliding motility, is employed by many bacteria : cyanobacteria .
1. What is the average diameter of bacterial flagella?
a) 2 nm
b) 10 nm
c) 20 nm
d) 50 nm
Answer: c) 20 nm
2. Which type of bacteria has a single flagellum at each pole?
a) Monotrichous
b) Amphitrichous
c) Lophotrichous
d) Peritrichous
Answer: b) Amphitrichous
3. The hook of a bacterial flagellum functions to:
a) Synthesize flagellin
b) Anchor the flagellum in the cell wall
c) Act as a flexible coupling between filament and basal body
d) Rotate the cell body
Answer: c) Act as a flexible coupling between filament and basal body
4. Which of the following components of the basal body is associated with the peptidoglycan layer in gram-negative bacteria?
a) L ring
b) P ring
c) M ring
d) C ring
Answer: b) P ring
5. In peritrichously flagellated bacteria, forward movement occurs when:
a) Flagella rotate clockwise
b) Flagella rotate counterclockwise
c) Flagella are stationary
d) Flagella vibrate
Answer: b) Flagella rotate counterclockwise
6. Which protein forms the filament of bacterial flagella?
a) Myosin
b) Tubulin
c) Actin
d) Flagellin
Answer: d) Flagellin
7. Which proteins form the proton channel in the flagellar motor of prokaryotes?
a) Mot A and Mot B
b) FtsZ and MreB
c) L and P rings
d) C and S rings
Answer: a) Mot A and Mot B
8. Which type of bacteria move through viscous substances using periplasmic flagella?
a) Cyanobacteria
b) Spirilla
c) Spirochetes
d) Cocci
Answer: c) Spirochetes
9. Gliding motility is commonly found in which of the following?
a) Vibrio cholerae
b) Escherichia coli
c) Cyanobacteria
d) Bacillus subtilis
Answer: c) Cyanobacteria
10. What powers the rotation of the bacterial flagellar motor?
a) ATP hydrolysis
b) Light energy
c) Proton or sodium gradient
d) GTP binding
Answer: c) Proton or sodium gradient
11. The flagellar motor of E. coli can rotate up to:
a) 90 revolutions/sec
b) 180 revolutions/sec
c) 270 revolutions/sec
d) 360 revolutions/sec
Answer: c) 270 revolutions/sec
12. The component of the bacterial flagellum that connects the filament to the basal body is:
a) Rotor
b) Shaft
c) Hook
d) Cap
Answer: c) Hook
13. Which structure in gram-positive bacteria is not present in the flagellar basal body as compared to gram-negative bacteria?
a) M ring
b) C ring
c) L and P rings
d) Shaft
Answer: c) L and P rings
14. What is the function of the Mot B protein in bacterial flagella?
a) Connects hook to filament
b) Forms part of the rotor
c) Anchors Mot complex to peptidoglycan
d) Synthesizes flagellin
Answer: c) Anchors Mot complex to peptidoglycan
15. Which bacteria has a lipopolysaccharide sheath around its flagella?
a) Escherichia coli
b) Vibrio cholerae
c) Bacillus subtilis
d) Streptococcus pneumoniae
Answer: b) Vibrio cholerae
16. The flagellar filament is composed of how many different types of protein subunits?
a) One
b) Two
c) Three
d) Multiple
Answer: a) One (flagellin)
17. Which bacterial flagellar mutants cannot swim?
a) Polyflagellin mutants
b) Polyhook mutants
c) Polysheath mutants
d) Motile mutants
Answer: b) Polyhook mutants
18. Bacteria change direction (tumble) when the flagella:
a) Stop rotating
b) Rotate faster clockwise
c) Reverse the direction of rotation
d) Lengthen the filament
Answer: c) Reverse the direction of rotation
19. In tethered cell experiments, when the flagellum is attached to a slide, what rotates?
a) The hook
b) The entire flagellum
c) The cell body
d) The basal body only
Answer: c) The cell body
20. What is the main difference between prokaryotic and eukaryotic flagellar movement?
a) Prokaryotic flagella whip back and forth
b) Eukaryotic flagella rotate like a propeller
c) Prokaryotic flagella rotate
d) Eukaryotic flagella are composed of flagellin
Answer: c) Prokaryotic flagella rotate
21. The primary protein forming the filament of bacterial flagella is:
a) Tubulin
b) Actin
c) Flagellin
d) Myosin
Answer: c) Flagellin
22. Which component of the flagellar basal body acts as a rotor in E. coli?
a) L ring
b) Hook
c) M and C rings
d) S ring
Answer: c) M and C rings
23. Which type of flagellar arrangement involves flagella all around the cell surface?
a) Monotrichous
b) Lophotrichous
c) Amphitrichous
d) Peritrichous
Answer: d) Peritrichous
24. Which of the following rings is embedded in the outer membrane of gram-negative bacteria?
a) M ring
b) C ring
c) L ring
d) S ring
Answer: c) L ring
25. The direction of rotation that leads to a “tumbling” movement in peritrichous bacteria is:
a) Clockwise
b) Counter-clockwise
c) Random rotation
d) Static rotation
Answer: a) Clockwise
26. In Vibrio alginolyticus, the flagella rotate at approximately:
a) 270 rps
b) 500 rps
c) 800 rps
d) 1100 rps
Answer: d) 1100 rps
27. The Mot A and Mot B proteins are involved in:
a) Flagellin synthesis
b) ATP-driven movement
c) Proton-driven motor function
d) Filament anchoring
Answer: c) Proton-driven motor function
28. The energy source for flagellar movement in bacteria is usually:
a) ATP hydrolysis
b) Sodium-potassium pump
c) Proton or sodium gradient
d) Glucose metabolism
Answer: c) Proton or sodium gradient
29. Bacteria such as spirochetes move using:
a) External flagella
b) Gliding motility
c) Periplasmic flagella
d) Pili and fimbriae
Answer: c) Periplasmic flagella
30. The hook of the flagellum serves the purpose of:
a) Anchoring the flagellum to the peptidoglycan
b) Generating rotational energy
c) Linking filament to the basal body and providing flexibility
d) Synthesizing flagellin
Answer: c) Linking filament to the basal body and providing flexibility
31. In Gram-positive bacteria, how many rings are present in the basal body of a flagellum?
a) 4
b) 3
c) 2
d) 1
Answer: c) 2
32. The L and P rings of the bacterial flagellum are associated with which structures, respectively?
a) Plasma membrane and cytoplasm
b) Peptidoglycan and capsule
c) Outer membrane and peptidoglycan
d) Cytoplasm and plasma membrane
Answer: c) Outer membrane and peptidoglycan
33. Which structure functions like a flexible joint between the flagellar filament and the basal body?
a) Rotor
b) Shaft
c) Hook
d) Cap protein
Answer: c) Hook
34. Flagella that are located at both poles of a bacterial cell are referred to as:
a) Amphitrichous
b) Lophotrichous
c) Peritrichous
d) Monotrichous
Answer: a) Amphitrichous
35. In bacterial cells, what is the role of the Mot B protein?
a) Synthesizes flagellin
b) Forms a part of the rotor
c) Anchors Mot complex to peptidoglycan
d) Provides flexibility to the hook
Answer: c) Anchors Mot complex to peptidoglycan
36. The “run and tumble” movement in bacteria is primarily associated with:
a) Cell division
b) Flagellar repair
c) Chemotaxis
d) Biofilm formation
Answer: c) Chemotaxis
37. A lipopolysaccharide sheath surrounding the flagellum is a feature of which bacterium?
a) Escherichia coli
b) Vibrio cholerae
c) Salmonella typhi
d) Staphylococcus aureus
Answer: b) Vibrio cholerae
38. The average rotational speed of E. coli flagellar motor is:
a) 150 rps
b) 270 rps
c) 900 rps
d) 1100 rps
Answer: b) 270 rps
39. Gliding motility is commonly observed in:
a) Spirochetes
b) Vibrio species
c) Cyanobacteria
d) Mycoplasma
Answer: c) Cyanobacteria
40. What happens when peritrichous bacteria rotate their flagella counterclockwise?
a) They tumble randomly
b) They move forward in a run
c) They stop moving
d) The filament detaches
Answer: b) They move forward in a run
41. Which of the following terms describes bacteria with a tuft of flagella at one end?
a) Monotrichous
b) Lophotrichous
c) Amphitrichous
d) Peritrichous
Answer: b) Lophotrichous
42. The protein that makes up the filament of bacterial flagella is:
a) Tubulin
b) Actin
c) Myosin
d) Flagellin
Answer: d) Flagellin
43. The part of the flagellum that acts as a motor in bacteria is located in:
a) The filament
b) The hook
c) The basal body
d) The cap
Answer: c) The basal body
44. Which rings are missing in the flagellar structure of Gram-positive bacteria?
a) M and S rings
b) L and P rings
c) M and C rings
d) C and S rings
Answer: b) L and P rings
45. What energy source drives the rotation of bacterial flagella?
a) ATP
b) Light
c) Proton motive force
d) Sodium-potassium pump
Answer: c) Proton motive force
46. What is the function of Mot A and Mot B proteins in the flagellum?
a) Structural support
b) Flagellin synthesis
c) Formation of the hook
d) Formation of the stator complex and proton channel
Answer: d) Formation of the stator complex and proton channel
47. Which flagellar component is directly connected to the filament and aids in flexibility?
a) Rotor
b) C ring
c) Hook
d) L ring
Answer: c) Hook
48. The “tumble” behavior in motile bacteria is caused by:
a) Clockwise rotation of flagella
b) Counterclockwise rotation of flagella
c) Cessation of flagella movement
d) Reversal of proton flow
Answer: a) Clockwise rotation of flagella
49. The structure responsible for rotation and anchoring of flagella in E. coli is:
a) C ring
b) S ring
c) L ring
d) M ring
Answer: d) M ring
50. Spirochetes move using:
a) External flagella
b) Pseudopodia
c) Periplasmic flagella (axial filament)
d) Gliding proteins
Answer: c) Periplasmic flagella (axial filament)