Cytoskeleton

What are the types of cytoskeletal filaments?

Actin microfilaments

Microtubules

Intermediate filaments

What is the purpose of actin?

Provides structural support, determines cell shape and cell migration/movement

found in cell periphery help form focal adhesions/adherens junctions

How are atcin microfilaments formed?

G-actin monomers undergo polymerisation into F-actin filaments

Nucleation, extension and steady state

asymmetrical with + end barbed and - end pointed

requires energy from G-actin bound to GTP hydrolysed to GDP, forms protofilaments

What is treadmilling?

Process where G-actin with GTP binds to + end whilst G-actin with GDP is removed at - end

highly dynamic

What are actins accessory proteins?

Profilin binds G-actin and promotes nucleation

Formin binds to actin and + end

ARP complex allows branching

Cofilin binds ADP actin which severs the filaments

Thymosin binds to GA-actin and prevents assembly

How do actin microfilaments cause cell movement?

Sense stimulus

actin polymerisation at the leading edge

G-ATP adds to + end, depolymerisation at - end causes filopodia

trailing edge is retracted, cytoplasm drawn forwards and new focal adhesions form at leading edge

What is a motor protein?

Protein that uses ATP/GTP to propel itself along filament

Use a globular head domain that binds to filament, ATP/GTP causes conformational change, filament release, conformational change and reattachment

Unidirectional

What are focal adhesions?

large dynamic protein complexes which connect cytoskeleton to ECM

needed for cell signalling, migration and withstanding mechanical forces

contain integrins

How can cell migration be studied?

Scratch wound assay-scratch made along monolayer of cells and observe as cells migrate

Transwell migration assay cells migrate through porous membrane

What is the function of microtubules?

organise organelle positions, vesicle movement, found in cilia/flagella in axonemes

cell division

What are microtubules formed of?

Formed from tubulin which are hetrodimers of alpha/beta

hollow tubes of 13 protofilaments, protofilaments are made of alpha/beta tubulin

assembly occurs at microtubule organisation centres (MTOCs)

uses gamma tubulin ring complex

nucleation when alpha tubulin binds to - end of gamma tubulin

elongation when GTP hetrodimer binds to beta tubulin at + end

uses tread milling

What is meant for dynamic instability?

unpredictable change from growth/shrinkage

Catastrophe/rescue

GTP hydrolysis at beta tubulin destabilises

What mechanism do MAPs have in neurodegeneration have?

Mutations in Tau gene cause hyperphosphorylation

causes detachment of Tau protein from microtubules

forms neurofibrillary tangles

disrupt neuronal function leading to neuron loss

How do dyneins and kinesins work?

Kinesin is a + end motor that moves in anterograde movement

Dyneins are - end motors that move in retrograde

require kinectin and dynactin

without package heavy chains fold to motor proteins to reduce ATPase activity

How do microtubules function in mitosis?

Instability helps formation of mitotic spindle from spindle pole

chromosomes attach to spindle and align at equator, move apart as spindle microtubules move to poles

astral microtubules anchor spindle pole

What is the function of intermediate filaments?

Provide structure

mechanical strength

mechanical coupling

What is the structure of intermediate filaments?

8-stranded ropelike structure

alpha helical region binds to other forming coiled-coil dimer

forms tetramer

8 tetramers form filament

What are nuclear lamins?

nuclear laminate complex of lamina, in the nuclear membrane

maintain shape, pore position

LINC complex links the nucleoskeleton and cytoskeleton

laminopathies are mutations in genes for lamina