cytoskeleton Flashcards
definition of cytoskeleton
cytoskeleton consist of filamentous bio-polymers (microtubules, F-actin and intermediate filaments) and oaf associated proteins that modulate the activity, dynamics and organisation of the cytoskeleton (actin binding or microtubule binding proteins, such as molecular motors)
filamentous bio-polymers in the cytoskeleton
microtubules, F-actin, intermediate filaments)
proteins associated with the cytoskeleton
actin binding or microtubule binding proteins, such as molecular motors
eukaryotic cytoskeleton provides
tracks that link the regions of the cell
skeleton
–> connects all parts of the cell–> supports motility–> helps spatial organisation
F actin location
found closest to the membrane
microtubules location
spans from the centrosome to the outside of the cell
intermediate filaments
found all around the cell
three classes of filaments that make up the cytoskeleton
f actin, microtubules, intermediate filaments
f actin also known as
microfilaments
F actin
7-9nm –> short range transport and cell migration
Microtubule
25nm –> long range transport and chromosome inheritance (mites, meioses)
<p>intermediate filaments</p>
mechanical strength
cytoskeleton as well as proving tracks for intracellular trafficking, also provides..
stability for the cell e.g. extreme example: membrane cytoskeleton of red blood cells make them stiff and strong
structure of F actin
- made up of G actin monomers-f actin is made up of 2 photo filaments-actin exists as monomers and polymers-F actin will release G actin- cell switches between g and f actin
most actin in the cell is
G actin
how many different actin binding proteins ar known
160
what do actin binding proteins d
they modify actin organisation
actin forms
cellular protrusion e.g. sterocilia on hair cells in the inner eare.g. microvilli on an intestine epithelium
examples of different formations of actin
stabilising, capping, depolymerising, cross-linking, severing, moving, bundling
ordered bundling
microvilli, sterocilia
dynamic crosslinking
stress-fibres and muscle
cross linking
network formation
myosin is used in
actin in a ‘moving’ formation
firkin, alpha-actinic is used in
bundling and stabilising
filamin, spectrum are used in
sequestering/recycling and branching
G actin is polymerised by
‘treadmilling’
what is treadmilling
adding subunits at one end, losing them at the other
without actin binding proteins
the cell would die e..g all the G actin would polymerise
the bundles actin forms make it
a strong molecule
single actin chains are
flimsy and week
cilia are just
huge bundles of actin
microtubules are made up of
beta and alpha tubular (tubulin dimer) and these polymerise into protofilliment (straight line) which joins to form a microtubule
13 protofilaments
form a microtubule
at one end of the microtubule there will be
Beta tubulin
at the other end of the microtubule will be
an alpha tubule
microtubule size
25nanometer diameter
without GFP what cannot be visualised
microtubules –> gives out light and make it look larger than it really is
tubular exists as..
dimers and polymers
tubular is fairly dynamic and this is due to
polymerisation behaviour
tubular is added and released at
one end of the polymer
polymerisation of tubulin- polymerisation
1)polymerisation- GTP-bound tubular dimers get added to ‘plus end’. A cap of GTP tubular stabilises the growing microtubule
polymerisation of tubulin- pausing
water is added to GTP tubular to form GDP tubular and phosphate. when polymerisation slows down (e..g not enough tubular available), the GTP cap disappears
polymerisation of tubulin- depolymerisation
-microtubule becomes unstable and depolymerises and this moment of transition is called a CATASTROPHE
polymerisation of tubulin- second polymerisation
GTP tubular can bind to the shrinking microtubule and establish a new cap.
The meant of transition is called a RESCUE EVENT
microtubules constantly switch from
growing and shrinking
growing and shrinking
dynamic instability
recue event
moment of transition when GTP tublin begins to bind again
GTP cap needs to be present for the
microtubule to grow
what reveals the difference in dynamic behaviour of microtubules and F-actin
speckle microscopy
which part of the microtubule is dynamic
the ends of the microtubule–> while incorporated tubular remains relatively stationary–> only change in colour at the ends of the microtubule
which parts of F-actin are dynamic
actin treadmills through the actin filament meshwork–> can see flow of action–> due to tread milling of fluorescent subunit throughout the actin filament
intermediate filaments
relatively unorganised and made of many different types of proteins. provide strength to organisms, since animal cells do not have a cell wall and the plasma membrane is liquid
which types of proteins are present in intermediate filaments
keratin, lamina, pimentos (ends are globular)
formation of intermediate filament
a coiled coil consisting of alpha-helices. made up of 2-3 helices, which wind around each other
alpha helices in intermediate filaments are often..
amphipathic
amphiphatic
charged at one site –> serves protein interaction
often intermediate filaments have a structural similarity but are
made up of different proteins e.g. keratin or vimentin
formation of intermediate filaments does not require
ATP or GTP –> self assemble into apolar filaments (not polar or dynamic)
nuclear lamina are made out of
intermediate filaments
lamins provide stability and organise the
nucleus
phosphorylation leads to
fragmentation of lamins
what allows cell movement
the intermediate filaments can be reorganised by disassembling into subunits
which skin associated structure are formed by intermediate filaments
nails, hair , eye (lens)
