Cytoskeleton: Overview Flashcards
Why should we care about the cytoskeleton
Fundamental cellular processes = cell division - mitotic spindle, motility, polarity, stability, diseases
Internal cytoskeleton makes cell move in space -by pushing it
What is cytoskeleton assembled by
Microtubules
Actin
Intermediate filaments
Describe actin thickness
7-9nm
Thin
Microfilaments
What are actin filaments
Microfilaments
F-actin = filamental actin
Describe microtubules thickness
Hollow tubes
Alpha beta tubulin dimers
Largest diameter = 25 nm
Describe intermediate filaments thickness
Intermediate filaments - various bundles
10nm - middle size
Describe structure actin filaments
Actin monomers assembled into filaments
ATP binding cleft - hydrolzye
37nm length, 8nm width
2 protofilamnets make up molecule = monomer actin assembles head to tail, helical nature, actin filament so also have side to interaction at form stable filament (also have vertical interactions)
Plus end = business end, form dynamics
Minus end = polarity
Where is actin found
Brush border cells - microvilli, increase surface area absorption
Under pm, forms adhesion - stability of cells
Muscle cells - important for contraction - actin myosin (motor molecule) filament - important for dynamics of actin
Describe microtubule structure
Hollow filaments composed of heterodimers
B and alpha tubulin= dimer, each has gtp binding spot, but only one gtp molecule hydrolyzed
50nm length, 25nm width
13 subunits
Lattice shaped structure
+ - ends
Describe ex where find microtubules
Centre of cell - bc polarity neg end usually attached to microtubule = anchors them in centrosome
Mitotic spindle - can extend and retract- do both
Describe intermediate filament structure
Heterogenous group of molecules made from alpha helical monomers
Less conserved across species than actin and microtubules
Alpha helical region monomer, not round or globule like, long and thin
Forms dimers = side to side interactions, interacts with other molecules of intermediate filaments, eventually assemble into bundles, thicker,
Not hollow
Where find intermediate filaments
Diameter = 10nm
Mesh work - neurons, nuclear lamina, epithelial cells
Do the 3 filaments have same mechanical properties
NAWWWWWWWWW
Some are more for structural support- not Motor, diff dynamics
What is persistence length
How long does it take elongated molecule to bundle or bend
Minimum length
What is persistence length of microtubule
> 1mm
Very big for cells, so very stiff = wont bend
Stiff rods, like plexiglass
What is persistence length Of actin
~10um = much shorter, not as long or rigid
Like twizzler
What is persistence length Of intermediate filament
<1um = very flexible, like rope, bends super easy
What makes up cytoskeleton mainly
Actin. And tubulin =main
Describe actin - functions/gen features
Atpase
Motility, contractility
Ubiquitous- found in all eukaryotes, also bacteria
Highly conserved sequence
Motor proteins - myosin’s,
Abundant —> 20% of all proteins in your muscles = actins
Describe microtubules - functions/gen features
Most found near/under cell membrane
Support, transport, organization - for cell shape, train tracks
Ubiquitous - found in all eukaryotes
Highly conserved sequence
Motor proteins - kinesins and dyenins - provide directionality = move in diff directions
Gtp ase
Describe intermediate filaments - functions/gen features
Structural support
Found in animal cells - many diff varieties
Divergent sequence s
No motor proteins
What does cytoskeleton provide
Shape
To neurons, neutrophils, goldfish keratocyte
What does cytokskeleton confer
Cells with internal organization and polarity
Ex = micorvilli =formed bc actin filaments underneath
Apical = -
Basal = +
Important for transport
Intermediate filaments link cells together
What does cytoskeleton enable
Intracellaulr transport
Middle of cell = mtoc - neg end
Dynenin = transport from + to - end
Kinesin = motor molecules transport reverse of dyenin
Purpose = go to edge of cell
Like roads for travel, motor molecules walk on train tracks (microtubule)
Describe movement of pigment granules
Melanosomes in melanophores - animals that change colour quickly
Dispersed melanosomes - spread out when high camp
Low camp = aggregated melanosomes, concentrated near neg end microtubule
Describe axonal transport
Specialized form of intracellular transport
Anterograde = transprt to axons
Retrograde = to get back to cell body
Some meow cells transported to synapse then recycled back into cell - need bidirectional transport
Fast axonal Transport moves vesicles and organelles along microtubuels at ~100mm/day
What does cytoskeleton help cells do
Helps cells move
Actin based motility = protrusions, actin molecules inside cell, moves cell across space
Microbtule based motility = cilia, sperm move
What does cytoskeleton form - microtubules
Dynamic and stable structures =
Mitotic spindle - dynamic, have to extend and retract - microtubule half life = short 45s (eb1 end binding protein, binds ends),
Axonemes - stable, stay here and do not go away (but stay for lifetime here, many proteins associate with it)
What does cytoskeleton form - actin
Dynamics and stable structures
Migrating cell - seconds to mins = move
Microvili - forms in hours, renew themselves
Hair cell stereocilia for life - actin turnover is weeks to years, can slowly regrow
T OR F= cytoskeletal filaments are static
nawwwww
Dynamic
Which end grows faster
+ end
At minus end = things happen slower
How are cytoskeleton filaments built
Asymmetric subunits that have diff numbers of protofilaments and display polarity
Actin and tubulin share common building principles
2 protfilamets for actin
13 for microtubuels tho
Describe self assembly and filament dynamics of tubulin and actin
Intrinsic properties
Actin = nucleation is slowest part, actin dimer not stable - likes to form filaments, if dimer = finds monomer = trimer, now have nucleus
Microtubule has nucleation process but less known
Describe actin - treadmilling
Hydrolysis on other end of where ad more monomers
Eventually rate atp hydrolysis catches up and monomer dissociates
Describe polymerization characteristics of actin and tubulin
S shaped population growth curves
Lag phase = slow, bc monomers need to form trimers, nucleation phase
Growth phase = fast, almost linear
Equilibrium phase= still many dynamics but length stays the same- continually lose and add molecules
Are actin and tubulin enzymes
Yurrrrrrr
Actin = atpase
Beta subunit tubulin = gtpase (only b tubtulin hydrolzyes gtp, to conduct instability of microtubuels)
Describe dynamic instability - microtubules
Shoot out and come back
What happens when hydrolysis of ntp in filaments
Resuslts in nucleotide caps
Describe ntp vs ndp bound
Hydrolysis of ntp in free monomers in solution is slow - hydrolysis in filament is fast
Ntp subunits like to assemble but ndp subunits like to disassemble
Subunits add in ntp state and dissociate in ndp state (ndp form less stable bc structural differences)
Kon(ntp)»Kon(dnp)=add
Kon(ntp)«Kon(dnp)=dissociated
When does ntp cap form
Rate of addition of subunits> hydrolysis rate
Ntp cap helps regulate dynamics
not hydrolyzing fast enough
When will loss cap and disassemble
Rate of Addition fo subunits < hydrolysis rate
Microtubule catastrophe = disassemble
Why are actin and tubulin ntpase based filaments
NEED for dynamics
Ndp form v unstable, ntp form - come together quickly
Ntp hdyrolysis renders filament inherently unstable - what we want for dynamics - treadmilling and dynamic instability
ATP vs gtp - bc need to regulate actin vs microtubules diff
What controls filament dynamics
Cells
Allows cells to sculpt cytoskeleton = where, when, how many filaments, how it grows, complex signalling, nothing random
How to control cytoskletal growth and organization
Manipulating the fundamental polymerization properties of subunits
Parameters cells can control = controlled by manu other proteins, can modify s shaped growth curve
Describe nucleation
If speed up = no lag phase
Describe elongation
Elongation - grows faster and makes longer - extends growth phase
How are cytoskeletal filaments regulated
Cells use accessory proteins to control every aspect of cytoskeletal dynamics - have to be conserved bc so many proteins associated with it
Bundlers and cross linkers, monomer binders (stabilize filaments), severing proteins (cut it up), nucleation factors
Is the cytoskeleton highly conserved
Yesssss
88% identical
97% simailr = many conserved differences
If differences - swapped for aa with simailr characteristics mostly
Describe viruses and cytoskeleton
Microtubule - cell edge to nucleus
Virus can hijack dyenin
Describe double cortex syndrome
Neurodevelopemtal disorder
Smooth brain
Point mutations in neuronal microtubule associated protein double cortin - dcx which results in failure in neuronal migration
One single aa change = causes disease
Describe diseases when reduced microtubule stability
Alzheimer’s disease (AD)
* tauopathies
* Parkinson’s disease (PD)
* Amyotrophic Lateral
Describe diseases when Hyperstable microtubules
Hereditary Spastic Paraplegia (HSP) - stiff lower limb
Describe tau and Alzheimer’s
Hallmark of neurodegenrative diseases = loss of neurons
Tau = microtubule associated protein
Tau tangles = dementia
Describe microtubules and cancer
Microtubule misrgeylation can cause anueploidy and cancer
Chrom lag behind = end up in wrong place
Microtubule drugs being used in chemotherapy - taxol paclitaxel, very hydrophobic = cannot be dissolved easily
Describe cytoskeleton as drug target
Epothilion d staibilzies microtubuels
Can give ppl small dosages
