cytoskeleton Flashcards
function of cytoskeleton
shape and modify response to environmental cues
intracellular and cell movement/ location of organelles
shape of cell
what is the cytoskeleton made up of?
complex network made of microtubules, intermediate filaments and actin filaments
function of microtubules associated with the cyotskeleton
organelle positioning
intracellular transport
function of intermediate filaments
mechanical strength when cell is stretched
strengthens the nuclear envelope
function of actin filaments
cell shape organelle shape involved in cell migration helical polymers flexible structure : 2D networks and 3D gels
how does the cytoskeleton function
Cytoskeleton is dynamic
The various filaments are made of monomers that continually polymerise and depolymerize
process of how the cytoskeleton works
The cell receives a signal (via receptors on cell membrane etc.)
Existing filaments in the cell depolymerize to form free monomers The monomers rapidly diffuse The monomers reassemble at a new site
what do accessory proteins regulate?
nucleation: the site and rate of filament formation
de/polymerisation
function
structure of actin filaments
Twisted chain of globular actin (G-actin, a protein monomer)
When the G-actin join together to form a filament/ polymer, it is called F-actin Thinnest form of cytoskeleton (7nm) Structural polarity Large number of ABP (actin binding proteins) in F-actin
what are the three isomers of actin?
Alpha actin, mainly in muscle cells
Beta actin, mainly in non muscle cells Gamma actin, mainly in non muscle cells
what is the polymerisation of actin?
G-actin added at either end of chain
Length is determined by concentration of G-actin or presence of ABP
ABP
proteins binding to monomers
Proteins that bind to monomers:
They determine if G-actin joins onto polymer chain Two types: Profilin – allows G-actin to join Thymosin – prevents addition of G-actin
proteins that bind to filaments
o Actin bundling proteins: F-actin in parallel bundles (e.g. microvilli)
o Cross–linking proteins: F-actin maintained in a gel like mesh work
o F-actin severing proteins: break F-actin into smaller filaments
o Motor proteins: transport of organelles and vesicles along actin filament
function of actin filament (muscle)
Interaction with myosin allows for muscle contractions
Arranged in paracrystaline integrated with different ABP
non muscle cells containing actin filaments
Cell cortex: thin sheet under the plasma membrane
With myosin: cleavage of mitotic cells (D) (cytokinesis)
cell migration
The cell pushes out protrusions at its front (lamellipodia & filopodia)
Actin polymerisation These protrusions adhere to the surface Integrins (link the actin filaments to the extracellular matrix surrounding the cell) Cell contraction and retraction of the rear part of the cell Interaction between actin filaments and myosin
structure of intermediate filaments
Each unit is made up of:
N-terminal globular head C-terminal Globular tail Central elongated rod like domain Units form stable dimers Every 2 dimers form a staggered tetramere Twists around each other to form rope structure
IFBP
Fillagrin: binds to keratin filaments into bundles
Synamin and piectin: bind desmin and vimentin. This links IF to other compounds (e.g. actin and microtubules) Plakins: keep contact between desmosomes of epithelial cells
function of intermediate filament in nucleus
Forms mesh structure
They line the inner face of nuclear envelope to strengthen it to provide attachment site for chromatin Disassemble and reform at each cell division as nuclear envelope disintegrates i.e. very different from the stable cytoplasmic intermediate filaments Process controlled by post translational modifications (mainly phosphorylation and dephosphorylation)
Structure of microtubules
Hollow tubes made up of protein – tubulin
Stiff and thick Ach filament polarized (+ and – end) Dynamic (Dis) assembles in response to cell needs
polymerisation of microtubules
Microtubules organizing centre (MTOC): specialized protein complexes where microtubule assembly starts
Centrosome: in perinuclear region: the MTOC of most cells Contains gamma-tubulin ring that initiates the microtubule growth Heterodimers of a and b tubulin constitute the microtubule It is a polarized growth (i.e. there is an end that grows faster (+end) than the other (-end)
function of microtubules
Intracellular transport
Act like railway tracks on which molecular motors run Different motors for different cargoes Directionality of filaments is vital (each motor only moves in one direction) Organizes position of organelles Hence, provides polarization of cells Directionality of filaments is vital
