Lecture 1B: Cell Locomotion Flashcards
What allows prokaryotic cells to move in their environments?
Motility devices that allow them to swim or crawl
What are the two major types of prokaryotic cell movement? (2)
Swimming and gliding
What is the phenomenon called when motile cells move toward or away from stimuli?
Taxis
What structure do many Bacteria use for swimming motility?
Flagellum
What is the analogous structure to flagella found in many Archaea?
Archaellum (pl. archaella)
- Tiny rotating machines that push or pull the cell through a liquid
- long, thin, appendages
flagella
What is the typical width of the appendages of bacterial flagella?
15–20 nm
How can flagella be observed under a microscope? (2)
- light microscopy
- electron microscopy
Different arrangements of flagella (4)
- polar
- lophotrichous
- amphitrichous
- peritrichous
Flagella are attached at one or both ends of a cell.
flagellation
polar flagellation
What is a group of many flagella (tuft) called?
flagellation
Lophotrichous flagellation
Tufts of flagella emerge from both poles of the cell
flagellation
amphitrichous flagellation
flagella located inserted around the cell surface
flagellation
peritrichous flagellation
The strength of the proton motive force affects the __ of flagella.
rotational speed
What is the maximum rotational speed of flagella?
Up to 1000 revolutions per second
What swimming speed can bacteria achieve relative to their size?
Up to 60 cell-lengths/sec
How do the swimming motions of peritrichously flagellated organisms differ from polarly flagellated organisms?
- Peritrichously flagellated organisms move slowly in a straight line
- Polarly flagellated organisms move more rapidly and continuously
True or False: Flagella rotate at a constant speed.
False
What is the significance of motility for prokaryotic cells?
Allows cells to reach different parts of their environment for resources or protection.
Flagellar structure and activity:
- __ in shape
- consists of several components
- filament composed of __
- __ rotating machine
- helical
- flagellin
- reversible
What is the main part of the bacterial flagellum called?
Filament
The filament is composed of many copies of a protein called flagellin.
What protein is the filament of the bacterial flagellum primarily composed of?
Flagellin
The amino acid sequence of flagellin is highly conserved in Bacteria.
What does the hook connect in the structure of the flagellum?
The filament to the flagellum motor in the basal body
The hook consists of a single type of protein.
In bacterial flagella, which rings are found in the basal body? (4)
L ring, P ring, MS ring, C ring
The L ring is embedded in the LPS, P ring in peptidoglycan, MS ring in the cytoplasmic membrane, and C ring in the cytoplasm.
What function do Mot proteins serve in the flagella?
They function as the flagellar motor (stator)
Mot proteins are embedded within the cytoplasmic membrane and peptidoglycan.
True or False: The flagellar motor is a reversible rotating machine.
True
It is composed of more than 25 proteins and is anchored in the cytoplasmic membrane and cell wall.
What is the main energy source for the rotation of the flagellum?
Proton motive force
Rotation is thought to be caused by a ‘proton turbine’ process.
Fill in the blank: The rotor of the flagellar motor consists of the central rod and the _______.
L, P, C, and MS rings
What role do protons play in the function of the flagellar motor?
They flow through the Mot proteins, exerting electrostatic forces that cause rotation
About 1200 protons are translocated by each rotation of the flagellum.
What two main components make up the flagellum motor?
Rotor and stator
The rotor includes the central rod and various rings, while the stator is comprised of Mot proteins.
How does the rotational speed of the flagellum relate to proton flow?
It is set by the proton flow rate through the Mot proteins
The flow rate is a function of the intensity of the proton motive force.
What structural adaptations can microbes make to their flagellar motors?
Adding or subtracting subunits from the stator and C ring
This changes the ‘gear ratio’ of the motor.
What are the components of the flagellar motor that help generate torque?
torque - a measure of the force that can cause an object to rotate about an axis
Mot proteins
These surround the rotor and function to generate torque.
What is a unique feature of the flagellar motor in gram-positive bacteria?
Only the inner pair of rings is present
Gram-positive bacteria lack an outer membrane. Only MS and C rings are present
What role do genes play in flagellar synthesis in Bacteria?
Several genes encode the motility apparatus, with over 50 genes linked to motility in Escherichia and Salmonella species
These genes encode structural proteins, export proteins, and regulatory proteins.
How does the flagellar filament grow?
from its tip, not its base
This is different from the growth of animal hair.
What is the first component synthesized in flagellar assembly?
The MS ring is synthesized first and inserted into the cytoplasmic membrane
Following the MS ring, other anchoring proteins, the hook, and the cap are synthesized.
What is the role of the export apparatus in flagellar synthesis?
The export apparatus shuttles flagellin molecules into a 3-nm channel through the basal body and hollow flagellar filament
This process facilitates the export of flagellin synthesized in the cytoplasm.
How many flagellin protein molecules are needed to make one filament?
Approximately 20,000 flagellin protein molecules
This large number indicates the complexity of flagellar structure.
Fill in the blank: Cap proteins assist flagellin molecules to assemble in the proper fashion at the _______.
flagellum tip
What happens to broken flagella?
Broken flagella still rotate and can be repaired with new flagellin units
New units are passed through the filament channel to replace lost ones.
True or False: The flagellum grows continuously until it reaches its final length.
True
What are the main components synthesized during flagellar assembly? (5)
The main components are:
* MS ring
* C rings
* Hook
* Cap
* Flagellin subunits
These components work together to form the complete flagellum.
Protein in the flagellar structure responsible for proton motive force
Mot protein (stator)
Protein in the flagellar structure that acts as a motor switch (counter-clockwise and clockwise)
FliF proteins
These two (2) proteins in the flagellar structure act as the motor (the engine of the flagellum).
- FliF protein
- Mot protein
- Composed of the FliF protein.
- Provides a scaffold for the assembly of other flagellar components, such as the C ring (cytoplasmic ring), motor proteins (MotA/MotB), and the export apparatus.
- a supramolecular complex embedded in the cytoplasmic membrane.
- membrane/supra membrane (MS) ring
MS ring
Ring in the flagellar structure the secures that rod on the periplasmic space/peptidoglycan.
P ring
Regulates the expression of the two outer-membrane porins OmpF and OmpC in response to changes in osmolarity.
Domain Organization of Histidine-Aspartate-Phosphorelay (HAP) Systems in Escherichia coli
EnvZ/OmpR pathway
This pathway involves a membrane-bound histidine protein kinase (HPK) EnvZ and a response regulator (RR) OmpR.
Senses changes in the redox state of components of the respiratory electron-transport chain
Domain Organization of Histidine-Aspartate-Phosphorelay (HAP) Systems in Escherichia coli
ArcB–ArcA HAP system
The HPK ArcB contains a PAS domain that plays a crucial role in this sensing mechanism.
Phosphoryl group transfer in the ArcB–ArcA system:
From a conserved His in the __ domain to a fused __ domain, then to a fused __ domain, and finally to DNA-binding __ __
What does this process regulate?; Domain Organization of Histidine-Aspartate-Phosphorelay (HAP) Systems in Escherichia coli
- ArcB kinase
- RR
- histidine-containing phosphotransfer (HPt)
- RR ArcA
This process results in the regulation of microaerophilic gene expression by ArcA.
What are the domains of the soluble HPK CheA in the chemosensory pathway of E. coli?
Domain Organization of Histidine-Aspartate-Phosphorelay (HAP) Systems in Escherichia coli
Five domains designated P1–P5 from the N terminus to the C terminus
CheA senses changes through transmembrane chemoreceptors, which induce trans-autophosphorylation.
- What are the two response regulators that compete for the phosphoryl group in the chemosensory pathway? (2)
- A motor-binding protein controlling flagellar motor switching.
- Controls the adaptation of the chemoreceptors.
Domain Organization of Histidine-Aspartate-Phosphorelay (HAP) Systems in Escherichia coli
1.1 CheY
1.2 CheB
2. CheY
3. CheB
Sporulation regulation of Bacillus subtilis:
- A single-domain RR regulated by two HPKs, KinB and KinA
- indirectly phosphorylates a DNA-binding RR, __, via a His residue in __.
Domain Organization of Histidine-Aspartate-Phosphorelay (HAP) Systems in Escherichia coli
SpoOF
- Spo0A
- Spo0B
Sporulation regulation:
HPK __ have numerous transmembrane domains. __, the other HPK, is soluble and has numerous PAS domains.
Domain Organization of Histidine-Aspartate-Phosphorelay (HAP) Systems in Escherichia coli
- KinB
- KinA
In the context of histidine–aspartate phosphorelay systems, what does the acronym HAMP stand for?
Function of HAMP?; Domain Organization of Histidine-Aspartate-Phosphorelay (HAP) Systems in Escherichia coli
Histidine kinases, adenylyl cyclases, methyl-binding proteins, and phosphatases
The HAMP domain serves as a linker domain in these systems.
True or False: HPKs are shown as dimers for simplicity in the figure.
False
Despite being dimeric in nature, HPKs are depicted as monomers in the figure.
What does the light-green rectangle represent in the figure?
Conserved, phosphorylatable His residues
This visual representation helps identify key residues involved in phosphorylation.
Fill in the blank: The phosphoryl group in the ArcB–ArcA system is passed to a DNA-binding RR called _______.
ArcA
What is the flagella analog in Archaea?
Archaellum
How does the archaellum impart movement to the cell?
Rotation
How does the archaellum compare in size to bacterial flagella?
Half the diameter
What is the approximate width of an archaellum?
10–13 nm
How do the filament proteins of archaella differ from bacterial flagellin?
Multiple proteins, no sequence homology
How many genes typically encode the major proteins of the archaellum?
7–12 genes
Name an archaeon known for its salt-loving nature and archaella studies.
Halobacterium
Name a heat- and acid-loving archaeon with well-studied archaella.
Sulfolobus
Name a methane-producing archaeon known for fast swimming.
Methanocaldococcus
What is the fastest known organism on Earth?
How fast?
Methanocaldococcus
500 cell lengths per second; 50 times faster than Halobacterium; 10 times faster than E. coli
What is one hypothesis for why archaella may generate less torque than flagella?
Smaller diameter
What bacterial structure is the archaellum structurally related to?
Type IV pili
- What energy source drives archaella rotation?
- What energy source powers the archaellum?
- ATP
- ATP hydrolysis
How does the archaellum rotate?
Clockwise and counterclockwise
What energy source powers bacterial flagella?
Proton motive force
How do archaella and flagella differ in energy mechanisms?
ATP vs. proton motive force
What does the difference in energy mechanisms suggest about motility evolution?
Independent evolution in Bacteria and Archaea
Around how many billion years ago did Bacteria and Archaea diverge?
3.5 billion years ago
What type of motility do bacteria use if they lack flagella?
Gliding motility
How does gliding motility compare to flagellar motility?
Slower and smoother
What cell shape is typical of gliding bacteria?
Filamentous or rod-shaped
What is required for gliding motility to occur?
Solid surface contact
Name a cyanobacterium that exhibits gliding motility.
Oscillatoria
What gram-negative bacteria use gliding motility? (3)
- Myxococcus
- Cytophaga
- Flavobacterium
Are there any known gliding Archaea?
No
How do cyanobacteria achieve gliding motility?
Slime secretion
What is the role of type IV pili in gliding motility?
Extension and retraction drag the cell
Which bacterium uses both type IV pili and an adhesion complex for gliding?
Myxococcus xanthus
What is unique about Flavobacterium gliding motility?
No slime or pili; uses protein ratcheting
What energy source drives Flavobacterium gliding?
Proton motive force
How does gliding motility help bacteria ecologically?
Resource exploitation and cell interaction
What is the directed movement of a microorganism in response to a stimulus called?
Taxis
What is the movement of bacteria toward or away from chemicals?
Chemotaxis
What type of taxis is a response to light?
Phototaxis
Why is taxis important for bacteria?
Resource access, avoidance of harm
What are the two types of movements in peritrichously flagellated bacteria?
Runs and tumbles
| clockwise and counterclockwise: If the flagellum is rotating counterclockwise, it pushes the bacterium forward (run). When it rotates clockwise, it pulls the bacterium backward (tumble).
In which direction do flagella rotate during a run?
Counterclockwise
What happens when the flagella rotate clockwise?
Tumble
How do bacteria determine the direction of movement?
Temporal sensing
What proteins detect attractants and repellents?
Chemoreceptors
What happens to runs in the presence of an attractant?
Longer, fewer tumbles
What movement pattern do bacteria follow in the absence of a gradient?
Random
What happens when a bacterium moves toward a repellent?
More frequent tumbles
What type of flagella arrangement does E. coli have?
Peritrichous
What type of movement do polarly flagellated bacteria like Pseudomonas use instead of tumbling?
Reversal
What bacterial genus uses flagellar stopping and Brownian motion for reorientation?
Rhodobacter
What is the method used to measure chemotaxis with a small tube?
Capillary tube assay
In a capillary tube assay, what happens when an attractant is inside the tube?
Bacteria accumulate
What form of taxis leads bacteria toward oxygen?
Aerotaxis
What part of a bacterial cell transmits sensory signals for movement?
Flagellar motor
If a repellent is inside the capillary, what happens to the bacterial count?
Capillary tube assay
Decreases
What do bacteria typically follow in natural environments?
Nutrient gradients
What microbial byproducts often attract bacteria?
Organic compounds, oxygen
What bacterial pigments absorb light for phototaxis? (2)
- Bacteriochlorophylls
- carotenoids
What is the name of light-induced taxis where cells tumble upon entering darkness?
Scotophobotaxis
What sensor initiates phototaxis?
Photoreceptor
What is the bacterial movement toward oxygen called?
Aerotaxis
What taxis involves movement toward or away from high ionic strength?
Osmotaxis
What taxis allows cyanobacteria to move toward water?
Hydrotaxis
