B107 - T6: Cystoskeleton & Cell Movement Prokaryotes

Cytoskeleton is an

internal network of fibers

Cytoskeleton strands can be chains of __ of bundles of __

globular proteins, fibrillar proteins

Describe the tubulin superfamily (FtsZ)

form band around midpoint of cell (Z-ring)
create strangulation leading to two daughter cells during division (by changing shape in ONE point). Heterodimers

What does inhibition of FtsZ lead to?

Prevention of cell division therefore long cells can grow (good for bacteria that want to infect)

Which proteins do tubular and action superfamilies use?

Globular

Describe MreB

part of actin superfamily
gives rod shape to bacteria (bacilli)

Describe RodZ. Is it cytoskeleton?

Transmembrane protein that works with MreB to shape prokaryotic cells. No, only creates a binding site for MreB

Describe ParM

Protein of action superfamily
Moves plasmids to oppsite ends of the cell (for cell division)
→ For LOW count plasmids

Describe cresentin

coiled coil filamentous protein
bends bacilli into curved shape

Mobility vs motility

Mobility: cell can move freely due to other things
Motility: cell can move by itself

How does the flagellum provide motility

Uses basal apparatus (motor) and filament attached by hook to move the hollow tube and therefore move the cell

Counter-clockwise vs clockwise motor rotations in flagella

Counter-clockwise: bundling and directional movement → run
Clockwise: random rotation

Chemotaxis

Movement directed by gradients of chemicals

How are runs and tumbles affected by chemotaxis?

Greater chemical concentration results in greater runs (bundling) and lower concentration result in greater tumbles (random)

Type IV Pili

Retractile protein filaments, move cell in a grappling hook like motion

Archaea flagella

Shorter and simpler, similar to type IV pili, powered by ATP (less efficient)

Periplasmic flagella / Axial Filaments

Found in spirochaete
External to plasma memb but internal to outer memb
Make cell rotate in corkscrew motion

Why would the body use axial filaments instead of flagella?

Efficiency: thinner and easier to move so beneficial in tough situation (ie. moving in mucous)

Compare prokaryotic and eukaryotic cytoskeletons

Both: maintain cell shape, move things during replication
Eukaryotes: move things during common physiological processes, propel the cell

Describe the 3 classes of cytoskeletal fibres in Eukaryotes

1. Microtubules: tubulin family, directionally polar, globular monomers

2. Intermediate Filaments: apolar, filamentous monomers

3. Microfilaments: action family, polar, globular monomers

Describe microtubules

• Hollow tubes made of tubulin heterodimers (a and B tubulin)

• Stiff and resists compression (bad under tension)

• Move cell and cell contents

• Serve as tracks for vesicle transport: motor proteins attach to mt and cargo and then transport it

Describe the motor proteins on the microtubules

Polar
Kinesin: moves toward positive, anterograde transport
Dynein: moves toward negative, retrograde transport

Eukaryotic cilia and flagella are made of ___ and are powered by ___. How do they differ?

microtubules, ATP
Cilia: beat asymmetrically
Flagellum: undulates side to side

How do flagella bend?

Due to anchorage and cross-linked proteins

Describe sperm vs egg movement

Sperm is motile, propels with flagellum
Egg is mobile, moved by. cilia on cells of fallopian tubes

How do chromosomes move?

Centrosome acts as microtubule organizing center (MTOC) and mt will buide chromosomes during mitosis (part of spindle apparatus)

Describe microfilaments

• g-actin polymerized into f-actin forms filaments (requires ATP)

• Microfilaments provide tensile strength, shape cell, and provide movement to cell and cell membrane

Cell cortex is made of

Microfilaments

Actin-Myosin system

Used for cell motion and muscle contraction
eg. used by plants

Actin vs Myosin

actin - thin
myosin - thick

How do amoeboids (and neurtrophils) move?

Crawling movement due to actin filaments and myosins pulling on them

Describe intermediate filaments

• fibrular protein (NOT globular)

• cable-like structures (high tensile strengh)

• toughen cell

• ANIMAL only (no prok, fungi, plants)

• Homodimer, coiled coil, strong disulfide bridges (stable)

Intracellular vs extracellular keratin

Intracellular - desmosomes: allows mechanical connections between cells
Extracellular - forms structures like hair, nails, claws (tough)

Lamin

Protein that forms nuclear lamina, anchors cytoskeleton to membranes