Prokaryote Cytoskeleton and Movement : BIOL 107

Lec 17 and lec 18

Cytoskeleton structure

biological fibers

Composition 1

chains of round (globular) proteins

Composition 2

bundles of thin (fibrous) proteins

Function 1

gives shape

Function 2

move things during cell reproduction

MreB structure

chains of round proteins

MreB function

makes cell rod shaped —> helps them to swim

give MreB example

E. coli

What happens if the cell can’t synthesize MreB?

They become round

are unaffected

become rod shaped

Crescentin structure

bundles of thin proteins

Crescentin function

makes cells curve —> also helps them swim

Crescentin example

C. crescents

What helps them swim?

the flagella

How can proteins (which are small) be used to build a cytoskeleton (which is large)?

by assembling into chains and forming dynamic networks within the cel

ParM role

involved in cell reproduction

FtsZ role

involved in cell reproduction

Mobile definition

cells can move

Motile defintion

cells can move by themselves

Pros of being motile

Chemotaxis – can swim towards food Dispersal – can spread outwards

Cons of being motile

Consumes resources and energy

Bacterial flagella composition

Hollow protein tube made of Flagellin proteins

Bacterial flagella structure

anchored in cell wall with cylindrical base

Bacterial flagella assembly

when new Flagellin travel inside flagellum cap

Bacterial flagella function

Entry of protons makes the entire structure rotate like a propeller

Proton gradient on plasma membrane made by

Proton Pump

Proton gradient on plasma membrane powers

Transporters and Flagella

How does an E. coli swim towards food?

runs and tumbles

Run meaning

(CCW) rotation moves the cell in a straight line

Tumble meaning

(CW) rotation = spin in place

Point of tumbling

change direction

Food sensors: If the concentration of food decreases the flagella is signalled to

do a tumble until the cell is pointing in the correct direction

continue running

do a brief tumble

Bacteria axial filaments structure

Like a flagella, but stuck to the cell wall

Bacteria axial filaments function

When the axial filament rotates, the entire cell is twisted like a corkscrew

How does a Spirochete swim towards food?

Corkscrews forwards = run

Corkscrews backwards = tumble

Which is better in thick environments (mud, mucus, etc.)?

Axial filaments

Which is better for speed?

Flagella