The Cyatoskeleton Flashcards
what is cytoskeleton and its function
it is proteins organised in fliament structures
function
- making cell shape
-providing mechanical strength
chromosome seperation
intracellular transport of organelles
cell movement
structure of cytoskeleton
actin filaments
intermediate filaments
microtubules
accessory proteins to cytoskeleton and why
cytoskelton binding, cytoskeleton associated and motor proteins
needed to maintain and regulate properties of each filament
dynamic cytoskeleton
made of polymers and can change quickly from polymer and moneymer
no covalent bonds
does not mean chaotic
Intermediate filaments (IF) structure
made of several proteins
order
alpha helical monomer
coiled coil dimer
staggered tetramer of two coiled dimer
two tetramers packed together
eight tetramers twisted into a ropelike filament
cross linked to actin and microtubules
intermediate differences from actin and microtubules
no defined polarity
no associated motor proteins
do not bind to nucleotides atp or gtp etc
very stable
why is IF useful for diagnostics
gene expression of IF is often unaffected
cancer cells lose shape of parent tissue
identification of IF proteins can pinpoint origin of tumors
4 types of IF proteins
Cytoplasmic
-Keratins - epthelia
neurofilaments - nerve cells
vimenting/vimentin-related - in connective tissue,muscle cell and neuroglial cell
Nuclear
nuclear lamins - in all animal cells
function of IF
Tensile strength; enable cells to withstand mechanical stress aka to stretch
structural support - deformable and reinforce
Keratins- info / location
make up hair nails skin etc
form strong network indirectly linked to neighour cells throught desmosome
hemidesmosomes connect epithelial cell to basal lamina
integrind bind to protein in plaques and to laminin in extracellular matrix
Vimenting info
required for trans-epithelial migration
endotehlial transmigation - ehite blood cells leave blood stream - process is impaired in vimentin mutant mice
desmin filaments maintain muscle structural integrity - filaments are tehered to z disk and develiop sarcomere - do not contract
Neurofilaments
have side arms
fill and pack cytoplasm of neurons
neurons in KO mice make axons with smaller diameter
IF in nucleus
meshlike rather than rope
cell shape, fix organelle localisation
present in all nucleated cells
line in inner face of nuclear envolope to strenthen and provide attachment site for chromatin
dissemble and reform at each cell division - different from stable cytoplasmic IF
process controlled by post translational modifications - aka phosphorylation/DEphophorylation
IF binding protein
Fillagrin - binds keratin into bundles
Synamin and plectin - bind desmin and vimentin link IF to other cytoskel as well as cell to desmosomes
Plakins - keep contact betwen desmosomes
Microtubules function
Establish polarity to movements and structures in interphase cell
participate in chromosome segregation during cell divison
estab;ish cell polarity during cellular movement
produce extracellular movement via cillia, flagella
microtubule structue
Made up of tubulin which has three formes alpha beta and gamma
alpha and beta form the tubule and gamma the core
tubulin subunit addition happens on plus end of microtubule with gtp+ tubulin
explain the “cap” of gtp on microtubules
growing microtubule
tublin with gtp binds to end addition faster than hydrolysis makes gtp cap
Shrinking
protofilament center peels away
gdp tublin is released to cytosol
explain the term dynamic instablity of microtubules
total mass of polymerized tubulin is constant but indicidual microtubules are dynamic
aka they can quickly dissasemble and change shape
goes from growth shrinkage catastrophe and rescue
Centrosome info ?
is the primary microtubule nucleation site aka from where micro tubules grow
contains ring of gamma tublin
often abnormal in cancer
cell polarity determined by ?
by muicrotubule-organising centers aka centrosome facing decided organisation of organelles and orientation of microtubules
why are mictobubles dynamic
Microtubule dynamics allow cell to quickly reorganise when building spindle
dynamics allow tubules to prob cytoplasm for specific object and sites aka search and capture
Search and capture
basically the tubules bound to the capping proteins remain where as the ones that dont are unstable
Microtubule associated proteins MAPS
- function as cross bridges connecting MTs
can affect MT rigidity and assembly rate
Microtubule associated proteins MTPS
- function as cross bridges connecting MTs
can affect MT rigidity and assembly rate
MAP functions
katanin - severs microtubules
stathmin - binds subunits, prevents assembly
Motor proteins
enzymes that convert atp hydrolysis directly into movement along cytoskeletal filaments
can move toward plus or minus end
carry cargo and mediate MT sliding
how MT motor found
cytosol squeezed from axon
atp added = movement
two fam of MT motor
Kinesins
move cargo to plus end
in mitosis pariticpate in spindle dynamics
dimers of 2 heavy and light chains - microbutbule and atp site on hea, cargo site on tail and ligth chains
Dyneins
move to minus
participate in spindle dynamics
power beating of cillia and flagella
large protein complex with many subunits
Kinesins and related proteins
look different but same motor domain
kinesin movement
they walk across MTS using clefts in tubules use atp
dynein structure and movement
made up of lots of proteins
ankyrin,spectirn etc
two classes
cytoplasmic
-carry in cytoplasm
axonemal
in cilla and flagella
motors that power them
celia and flagella
specilaised MT structures
cillia- line epithelial tissue in resp track to move matter out
line oviduct o push egg
non motile - detect signals
flagella - allow sperm to swim
- done by dynein
disease - fertility , respiratory
motile axoneme
nine duplets one center and multiple proteins
Actin functions
allows cell to adopt different shapes
e.g. villi, contractile bundles, sheetlike protusions and contractile ring
Actin structure
7nm in diameter
less rigid than MTS
plus end - fast grow
minus - slow
monomers polymerise into helical chain
Actin binding
using polymerisation actin atpase cleave atp to adp
atp hydrolysis actds as a molecular clock
older actin filaments with adp are unstable and dissasemble
Nucleation of actin
is the rate limiting step in the formation of a cytoskeletal polymer
what controls actin structure and function
actin binding proteins
they bundle protein, act as motor protein, side binding protein, severing protene
explain structure of actin in microvili
plus end near top
crosslink of villin and fimbrin
and lateral sidearm
actin in cell cortex
mesh and used filamin dimer to link filaments
Actin polymerisation
can produce pushing force
at front of cell can edge cell foward
used in phagocytosis - formation of pseudopods
intracellular movement and cell to cell spreading of pathogens
also drives protusion of membrane
model for actin polymerization
Nucleation is catalyzed by proteins including actin related proteins (ARPS)
differenses on sides and minus end prevents arps from forming filaments on their own
ARP complex nucleates actin growth from minus end allowing elongation on plus end
ARP complex can attach to side of another actin filament while remaing bount to minus end of nucleated one
arp is more efficient when bond to previous actin filament
what do we need for no branching in actin
formins which are able to form straight unbranched filaments . they are dimeric and each subunit has a binding site for actin monomer
Diferent proteins useful for actin
Thymosin - actin monomers bound to this are locked and cannot associate to either end of actin filament
Profilin- binds to opposit of atp binding cleft, binds to plus end and unable to bind to minus
Tropomyosin - stabiliseis filament by binding to 7 adjacent actin subunits prevents other proteins binding to actin
cofilin -destabilises actin filaments by twisting tightly and breaking it
examples of cross linking assemblies of actin
contractile bundle- stress fibre
gel-like networjk - cell cortex
tight parallel bundle - protusions of cell
contractile vs parallel bundle
contractile - loose packing allows myosin 2 to enter
parallel - tight pack no myosin 2 entry
Listeria
colonises epithelial cells
uses actin to shoot protusion into em
uses actin based comet tail to move
Myosins
actin based motor proteins
convert ATP hydrolisis into movement along filament
some move cargo others slide actin
actin and atp binding sites in n-terminal head domain
walk along filaments
