Microbial movement – crawling, gliding and swimming Flashcards
In order to utilise nutrients
microorganisms need means of locomotion
examples of locomotion
1) e.g. Chlamydomonas moving towards light – phototaxis
2) Dictyostelium cells aggregating – chemotaxis
3) Bacteria and eukaryotic cells migrating towards food sources - chemotaxis
There are several models of how chemotaxis works (the same models hold for phototaxis as this like chemotaxis depends upon signal perception)
1) temporal model
2) spatial model
3) pseudospatial
whats the temporal model?
assumes that a cell ‘remembers’ a concentration of signal at T0
whats the spatial model?
assumes cells can determine the difference in concentration around themselves
whats the pseudospatial model?
similar but depends upon the cell actively probing the environment e.g. with pseudopodia
How does movement take place (crawling) in Dictyostelium ?
Movement takes place by successive elongation of the leading edge by extension of pseudopodia, combined with adhesion to a substrate surface
Motion in Dictyostelium depends on…
Motion depends upon the combined effects of a pull from the front and a push from behind.
Describe crawling in Dictyostelium
1) protrusion
2) adhesion
3) traction
4) de-adhesion/tail retraction
5) protrusion
Describe the dynamic system of motility in dictyostelium
Actin reversibly polymerises so cytoskeleton is continuously formed and broken down
Myosin also associates with …
… both the leading and lagging edges of the cell providing the force to move the cell
An alternative model is that …
… cell movement is due to growth of membrane – but in the case of Dictyostelium this cannot account for speed of cells
how is invasion of erythrocytes by Plasmodium accomplished ?
Both invasion of erythrocytes and movement along the matrix of cells in Plasmodium is accomplished by use of the actomyosin motor.
Conformational change in …
… actin ratchets against actin filaments causing a force which provides forward movement
Many bacteria move by …
… a ‘gliding’ motion.
Many bacteria move by a ‘gliding’ motion
According to some research, how does this work?
Some research suggests attachment and contraction of Type IV pili is important in gliding in certain bacteria including Myxococcus and Clostridium
Describe gliding movement
- extension and attachment of type IV pilus
- contraction moving cell towards attachment point
- release of pilus and re-extension
Eukaryotic cilia and flagella have …
…have an identical structure.
Eukaryotic cilia and flagella have an identical structure. However, they…
…differ in their length.
flagella and cilia consist of…
… an axoneme (2 microtubules) in the centre and 9 pairs of microtubules around the periphery (9+2 structure).
Connections between the axoneme and the outer microtubules are by…
… nexins and dynein.
Eukaryotic cilia and flagella consist primarily of …
… microtubules
Movement of eukaryotic flagella and cilia is generated by …
… the slippage of one microtubule against another
Movement of eukaryotic flagella and cilia is generated by the slippage of one microtubule against another.
as the microtubules are connected this results in …
… bending of the microtubule creating a ‘whiplash’ like motion.
Slippage is caused by movement of …
… dynein arms – on hydrolysis of ATP (energy)
Slippage is caused by movement of dynein arms – on hydrolysis of ATP (energy)
the dynein …
… head moves towards the minus end of the microtubule causing a shift of one microtubule against another – so the energy dependent movement of the dynein head causes bending.
the bacterial flagellum is made of…
… multiple molecules of flagellin.
The flagellum is …
… sinusoid and movement comes from the force imparted by it against liquid molecules in the media
Each species has a …
… characteristic wavelength
The drive for the movement of the rotary motor associated with the bacterial flagellum is provided by…
… the flux of protons over a gradient.
In Gram negative bacteria protons move from …
… high concentration in the periplasmic space to low concentration
what complex do protons move through in driving the rotary motor of bacterial flagella?
the Mot complex
The movement of protons through the Mot complex (surrounding the basal body of the flagellum) …
… drives rotation
where is the Mot complex?
surrounding the basal body of the flagellum
chemical energy is converted to …
… kinetic energy
for swimming bacteria, chemical energy is converted to kinetic energy via…
hydrolysis of ATP to ADP
for bacterial flagella using a proton motive force, chemical energy is converted to kinetic energy by…
… the movement of protons
Dead wood is a …
… huge potential nutritional resource for animals
Dead wood is a huge potential nutritional resource for animals – however animals lack the enzymes able to break down cellulose
Termites accomplish this by …
… utilising a protozoan called Mixotricha.
Mixotricha itself is a …
… eukaryote and also cannot produce cellulase
Endosymbiosis with cellulase digesting bacteria enable …
… Mixotricha to accomplish this, so providing the termite with food
Myxotricha has other endosymbionts, including …
… a mitochondrion and rod shaped bacteria adhered to its outside.
Myxotricha also has an…
… ectosymbiont
Myxotricha also has an ectosymbiont! What is embedded in its cell periphery ?
Thousands of spirochaete bacteria are embedded in its cell periphery.
These spirochaetes have …
… rotating flagella which provide the motive force by which Myxotricha moves around.
