Lecture 18 Outline Cell Motility

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3 Basic Methods of Cell Movement

- Swimming
- Crawling
- Gliding

-Usually involves ATP generated movement of cellular components relative to cell membrane. In eukaryotes, the structures usually involve the cytoskeleton.

Methods of Cell Movement: Swimming

-propulsion through solution (bacteria, protozoa, ciliates, clams, fish)

Methods of Cell Movement: Crawling

-systematic attachment and detachment of cell surface to substratum (amoeba)

Methods of Cell Movement: Gliding

- movement of cell generated by secretion (&/or attachment) and movement of mucilage (algae, diatoms, blue-green bacteria)

2 Main Kinds of Swimming

-propeller - corkscrewing your way through solution (bacteria)
-modified breast stroke - ciliates and flagellates

Propeller

-Bacterial Flagella (Do not confuse with eukaryotic flagella)

- Main shaft composed of a single polypeptide - flagellin
- Protein aggregates into a hollow helical coil
- Protein for elongation or repair of flagella comes from inside cell
> subunits diffuse up the hollow center - limits length of shaft
> new subunits add on at tip
- Coil is attached into the bacterial membrane by way of a shaft and collar, several different proteins.
- Rotation of coil drives bacteria through solution, like a propeller
- Rotation can be in either of two directions
> counter-clockwise - cells move in a relatively straight direct
> clockwise - cells tumble randomly
- Powered by a H+ gradient
> bacteria generate proton gradient in space between plasma membrane and cell wall
> use gradient to make ATP, and to power the rotation of a plate (attached to coil) relative to the shaft
- Receptors on cell surface which monitor cellular conditions
> if conditions better than they were previously - increase the relative amount of time moving counter clockwise (longer runs)
> if condition is worse than previously - increase the amount of clockwise movement (more tumbles, shorter runs, increased time in same location)

Propeller: Rotation, Powered

> counter-clockwise - cells move in a relatively straight direct
> clockwise - cells tumble randomly
- Powered by a H+ gradient
> bacteria generate proton gradient in space between plasma membrane and cell wall
> use gradient to make ATP, and to power the rotation of a plate (attached to coil) relative to the shaft
- Receptors on cell surface which monitor cellular conditions
> if conditions better than they were previously - increase the relative amount of time moving counter clockwise (longer runs)
> if condition is worse than previously - increase the amount of clockwise movement (more tumbles, shorter runs, increased time in same location)

Eukaryotic Flagella (undulapodia): describe

- Much more complex than bacterial flagella
- Composed of many different proteins in both flagella and base
- Surrounded by plasma membrane, entire flagella is appendage of cell
- Purpose of flagella is to beat in a wave-like fashion, propelling the cell with a "breast stroke"
- Can be organized in many different ways
> many smaller appendages arranged in organized arrays (cilia)
> two longer appendages which beat in controlled synchrony

Eukaryotic Flagella (undulapodia):main structure, flagella, movement

- Main structural elements of flagella are microtubules
> Main shaft has 9 sets of doublet microtubles and usually 2 central single microtubules (9+2)
> Microtubules are attached to the base of the flagella by way of a complex cylinder of material containing 9 sets of triplet microtubules and connecting material
• this structure (basal body) is virtually identical to centrioles
- Flagella moves by the systematic sliding of microtubules past one another
> Movement of two filaments past one another causes bending [Demo]
> Beating is driven by the controlled sliding of microtubule doublets past one another
> Movement is driven by a mechanochemical protein called dynein
- As discussed before, this type of movement is driven by mechanochemical motor proteins which undergo attachment and detachment to microtubules
• mechanochemical protein is dynein - has three heads and stalks (some species have two)
• connects the A (complete MT) with the adjacent B MT
• structure is held together by nexin (holds together MTs), and spokes (connect MTs with central area)
• coordinated release of nexin links (Possibly Ca2+ sensitive) is thought to help regulate direction of movement
• must be attached at base for bending to occur, dissociated doublets slide past one another

Amoeboid movement

This movement seems to based upon the ability of controlling actin microfilaments to change the viscosity of the cytoplasm
- actin filaments can become crosslinked forming a gel-like area
- actin filaments can become fragmented, forming more solution like cytoplasm
- coordinated control by actin-binding proteins
- as amoeba move there is area of leading material that is stretched forward - pseudopodia
- at end of leading edge the cytoplasm has much higher viscosity
- EM studies have shown that there is a tight cross-linked set of actin in front of pseudopod
- basic structure - edge of gelled material, inner core of movable cytoplasm
- by slight contraction of middle area, cytoplasm is "squeezed" into pseudopod
- as new material is squeezed into the front - new "gel" is formed and old gel is dismantled

Gliding: two kinds

- movement with no change in cell shape
Two major kinds
blue-green bacteria
diatoms

Gliding: blue green bacteria

- filaments can move in a relatively straight path
- usually associated with a helical turning of the filament as it moves
- may be due to usual helical pattern of cellular structures in the filament
- not clear how, may be due to secretion of cellular material from pores in the cell wall

Gliding: diatoms

- gliding movement, but more regulated
- associated with those diatoms which have characteristic slits in their hard cell wall
- several cell types have been shown to have actin bundles in the cytoplasm underneath the slit
- again, not clear exactly how they move, possible cellular secretion coupled to transmembrane movement
- mucilage strands are secreted through the slit, then they are moved by actin cables, using ropes to pull cell along

Intracellular Motility

-Also directed movement of intracellular particles (only in eukaryotes) - often along cytoskeletal filaments.
-Basically as described before in talk on cytoskeleton - vesicle can associate with a motor protein, and move along cytoskeletal filaments

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