cytoskeleton

classes of cytoskeleton

• actin filaments

• intermediate filaments

• microtubules

actin is found in

all eukaryotic cells

actin filaments are

a polymer made up of actin monomers

exists as a globular protein 

why are rings of actin important in axons

maintain the structure and diameter of axon

therefore important for action potentials

actin is organised in

bundles or meshed networks/branched arrays

actin is important for

force exertion

cell movement

cell division

actin based structures in motile cells

• stress fibres

• lamellipodium

• filopodia

actin in yeast cells/yeast budding

high density of actin at edges of yeast budding

the actin filaments force the yeast cells to divide/ cytoplasm to divide

mutations in actin cause multiple disorders including

muscular dystrophy

haemolytic anaemias

polymerisation of actin filaments

• G-actin reversibly polymerise to form F-actin, a double-helical actin filament with a diameter of 5–8 nm.

• Actin filaments are polar, with a plus (barbed) end and a minus (pointed) end.

• Subunits add to both ends, but faster at the barbed end.

• ATP-bound actin adds to the filament; ATP is then hydrolysed to ADP, making the filament less stable at the pointed end.

• As actin adds at the plus end and dissociates at the minus end, monomers appear to move along the filament — this is actin treadmilling.

what is microtubule

filament of tubulin monomers

a sarcomere is

the basic unit of contractile muscle fibres

composed of actin and myosin

myosin II is a

motor protein that interacts with F-actin

4 classes of intermediate filaments

• keratins → in epithelia

• vimentin & vimentin-related → in connective tissue, muscle cells, glial cells

• neurofilaments → in nerve cells

• nuclear lamins → in all animal cells

when pressure is applied on cells

the tension can spread across the intermediate filaments

keratin monomers are

fibrous proteins

microtubules originate in

MTOCs such as the centrosome

MTOC

microtubule organising centre

point where polymerisation starts

why are microtubules in cilia in lung cells important

for sweeping away mucus, keeping pathogens away

kinesin

type of motor protein that act on microtubules

from minus to plus end

dynein 

type of motor protein that acts on microtubules

move from plus to minus end

movement of motor proteins along microtubules

use ATP to generate kinetic energy and carry proteins, RNA, vesicles, organelles etc. along

lamins are

intermediate filaments that support the nuclear envelope

centrosome is

cell’s organising centre for microtubule growth

Myosin filaments

are bundles of motor proteins that interact with actin fibres in muscle

which factors destabilise microtubules

• vinblastine

• nocodazole

• colchicine

by inhibiting microtubule formation

arrangement of cytoskeleton

a form of dynein enables

cilia to beat