Cells move to find food, shelter and safety.
| Flagellated | Flagella are polar, bipolar, lophotrichous (bunch at 1 end), monotrichous, amphitricious and petrichous (E. coli). To view with high contrast, use die, electric microscope, or dark field. Help w/ attachment.
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| Random Walk | Cells move toward attractants (c-source), from repellent (organo acid) and indifferently to control (media). Requirements are (a) sense external signal, (b) respond to signal (internal signal), (c) modify behavior and (d) scalable response. E. coli: Tumble, run, tumble. Tumble every 10th sec, run 10 secs, T req of both 13 /sec. Random walk. The random walk is biased. As concentration of attractant goes up, the tumble frequency goes down. E. coli run ccw (bundle) and then unbundle and go cw to tumble. When the attractant concentration is high, the cw frequency goes down, unbundled is less likely to occur, and running (ccw) happens more often. Is the propellor or the whip model correct? Howeder saw that flagellum spin ccw, stop, cw, stop, ccw, etc. Algae is a good model organism for studying motility. Cilia are on protozoans (paramecium). Microtubule-based, extend from basal body, surrounded by cell membrane, mechanism=sliding & bending of microtubules. Running is more often in presence of attractant. |
| Ameboid Motion | Extend pseudopod…mechanism: actin, controlled polymerization of actin filaments at leading edge pseudopod….used by entamoeba protozoan for dyssentary, slime molds. |
| Gliding Motility | Smooth gliding with no apparent change in cell morphology. Example: toxoplamsagondii (very important)…malaria plasmoduan. Gliding motility somehow involves actin. Demonstrate via mutation to actin. |
| Length | # Per Cell | Motion | |
| Flagella | Long; > 5µm | 1-2/cell | Whiplike |
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| Cilia | Short; <5µm | 100s/cell | Breast stroke |
Axoneme (9+2 structure, MT bundle) is 9 pairs of microtubules around central pair. Microtubules are made of a- and B-tubulin). Surrounded by cell membrane. Dynein, ATP-dependent molecular motor, attached to tubulin. Whip-like motion. Cilia are structurally the same.
1) Isolate intact flagellum
2) Remove membrane with detergent
3) Left with flagellic cytoskeleton.
4) Flagella still moves (sliding filament model)
Mutagenize wildtype cells so they cannot move. You can find the tightest colonies, or you can put them in a solution and find which ones sink to the bottom. Isolate a mutant, grow it up, and then grow up the ones from the bottom yet again. Transfer bottoms to fresh flask, and if they are motility mutants then all should settle. You then study those under a microscope. The mot(-) cells sometimes had no, stubby or rigid flagella. The ones with rigid flagella lacked radial spokes, so those are required for flagellic motility.
To determine which flagellar component was most important, the following experiment was performed.
There is another experiment possible, although it is not as reliable, where you screen for small colonies after transposon tagging.
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