CMB1004-L4: cytoskeleton and cell movement

Why is the cytoskeleton important?

Responsible for cell shape and movement, positions organelles within the cell, directs transport between intracellular compartments, associated with motor proteins, highly dynamic and regulated.

Where are intermediate filaments found?

Cytoplasm and nucleus.

What is the structure of intermediate filaments?

• Alpha helical coil of 8 tetramers to form the filament.

• strong flexible polymer

What are some examples of cytoplasmic intermediate filaments?

Keratins, vimentin and neurofilaments.

What is an examples of nuclear intermediate filaments?

Nuclear lamins- line the inner face of the nuclear membrane, keeps the structure open

What is the function of the intermediate filaments?

To provide strength and prevent excessive stretching.

Where are microtubules found?

The cytoplasm only.

What is the function of microtubules?

Organelle and vesicle shuttling, segregation of chromosomes during mitosis (spindles) , facilitate movement.

What is the structure of microtubules?

• Alpha and beta tubulin that form a cylinder of 13 protofilaments.

• plus end- beta

• minus end- alpha

• polymers of the monomer tubulins joined by GTP and disassembled with GDP

• rigid and dynamic, polar

• emerge from one centre

What are two examples of microtubule motor proteins?

Kinesins and dyneins.

structure and activity of microtubule motor proteins

kinesins and dyneins

• have head and tail region

• globular head binds to microtubule using ATP. then hydrolyzed to create movement

• kinesins move towards plus end of microtubule

• dyneins move towards minus end of microtubule

• tails bind to what needs to be moved golgi, vesicles

how do microtubules / dyneins move cilia- 2 steps

1. ATP hydrolysis drives the sliding of microtubules

2. microtubules stuck together so when ATP hydrolysed the MT bend/flexes

What is the structure of actin filaments?

• F-actin wrapped around each other.

• polymers of actin joined with ATP

• 2D networks in bundles

• polar

What is the function of actin?

Cell motility and contraction, adhesion

Where is actin found?

The cytoplasm.

how are actin filaments formed

• globular (G-actin) monomers added to each end

• forms polarised filaments (F-actin)

• polymerisation uses ATP hydrolysis

• this is organised by interactions with actin binding filaments

how do actin filament motor proteins work

• myosins are the family of actin motor proteins

• globular heads bind ATP and to actin filaments

• ATP hydrolysed, driving movement

• tails bind structures like plasma membrane vesicles or other myosin

• can move cell or cellular components

myosin I structure and activity

• one head/tail

• intracellular organisation

• moves cargo along the actin filament

• in all cells

structure and activity of myosin II

• dimer

• forms filaments and contractile structures

• in muscle cells

what is spectrin

a 4th type of filament, cytoskeletal protein that lines the inner plasma membrane

function of spectrin

• provides crucial mechanical strength stability and shape for the plasma membrane

• links membranes to motor proteins and all major filament systems