Cell movement/Microtubules

Cell motility

movement of a cell through an environment, an environment past of through a cell, or the movement of components in the cell

Contractility

used to describe shortening of muscle cells, specialized form of motility

What do MT and MFs do to generate movement?

they provide a scaffold for motor proteins that produce motion at the molecular level

2 eukaryotic motility systems

1. microtubule based motility

2. microfilament based motility

example of microtubule-based motility

fast axonal transport in neurons; the sliding of MTs in cilia and flagella

example of microfilament-based motility

muscle contraction

Fast axonal transport

the process by which proteins produced in the body are transported to the nerve ending

Two proteins responsible for fast axonal transport

Kinesin 1 and Cytoplasmic dynein

Kinesin 1 function in fast axonal transport

involved in ATP-dependent transport toward the plus ends (away from centrosome)

transport mediated by kinesin 1 is also called

anterograde axonal transport

cytoplasmic dyein role in axonal transport

moves particles (cargo) in the opposite direction

axonal transport mediated by cytoplasmic dyein is also called

retrograde axonal transport

Kinesin composition

two dimerized heavy chains and two light chains

Kinesin heavy chains

contains globular domains that attach to microtubules and ATP, a coiled-coil stalk, a lever-like neck that connects the two, and a tail

Kinesin light chains

associated with the tail and bind to cargo

Kinesin movement

looks like walking, with the two globular head domains taking turns as the front foot

each kinesin molecule exhibits

processivity

How does kinesin detach?

by releasing bound ADP and aquiring a new ATP

Where are dyeins found?

in Axonmes and the Cytosol

What do dyeins associate with?

a protein complex called dynactin

dynactin function

helps link dynein to cargo

All dyenin are ____ and their movement is

(-)end-directe; ATP-dependent

how many types of axonemal dyeins are there?

7

How are vesicles transported to and from the golgi complex?

they are carried by MT motors on microtubule tracks

motile appendages of eukaryotic cells

cilia and flagella

What is crucial for the movement of cilia and flagella?

Microtubules

Where and how much are cilia found?

found in large numbers on the surface of ciliated cells

cilia pattern and direction of force

display an oar-like pattern of beating, generating a force parallel to the cell surface

Flagella function

move cells through a fluid environment

Are cilia or flagella longer?

flagella

How many flagella are found on one cell?

one or a few per cell

Flagella movement and force direction

move with a propagated bending motion, which generates a force parallel to the flagellum

Common structure between cilia and flagella

the axoneme

the axoneme is connected to ___ and is surrounded by____

a basal body; an extension of the cell membrane

What is between the axonemme and basal body?

a transition zone

transition zone function

place where the microtubules take on the pattern characteristic of the axoneme

Basal body structure

looks like the centriole, with nine sets of tubular structures around the circumference

Each set of tubular structures in a basal body is a

triplet with three microtubules that share common walls

Axoneme characteristic pattern

9+2 pattern; 9 outer doublets and 2 Microtubules in the center

central pair

2 microtubules in the center of a basal body

Primary flagella

used in sensory structures

Primary cilia structure

9+0 structure; lack the central pair

Are primary cilia motile or non motile?

non-motile

Primary cilia are important for

cell signaling pathways and development

Axonemal dynein is involved in

the sliding of MTs against each other, which bends the axoneme

how does dynein form links between microtubules?

forms links between doublets; one doublet serves as the cargo while dynein moves along the other doublet

How are adjacent microtubule doubblets joined?

interdoublet links

interdoublet links function

limit the extent of relative movement of doublets

What protein links adjacent microtubule doublets?

nexin

Doublet sliding within the axoneme causes

cilia and flagella to bend due to the movement of dynein

what two structures are responsible for bending of cilia and flagella?

crosslinks and spokes

Intraflagellar transport (IFT)

tubulin subunits are shuttled to and from the growing flagellum tip by both + and - end directed motor proteins

How are components added t o growing cilia and flagella?

intraflagellar transport

Kinesin role in intraflagellar transport

moves material to the tips of the flagella

Dynein role in intraflagelllar transport

brings material back towards the base