2-cell anatomy: cytoskeleton Flashcards
the cytoskeleton can form ________ and can be ____ and _____
stable structures
dynamic
adaptable
the cytoskeleton is involved in numerous processes related to ______, ______, and ______
shape
support
locomotion
3 main types of protein filaments
- microtubules
- actin filaments
- intermediate filaments
_______ regulate filament assembly and dynamics
cytoskeletal associated proteins (accessory factors)
cytoskeleton general properties:
- filaments self assemble from small subunits
- subunits associations with a filament are weak and noncovalent
- filaments consist of multiple protofilaments that associate laterally with each other which allows for overall thermal stability for filaments
- accessory proteins regulate assembly of new filaments
breaking a filament in the middle requires breaking sets of _____ in several protofilaments. This results in overall _________ for the filaments
longitudinal bonds
thermal stability
removing a subunit from the ends requires less energy, leaving the filament ends as _________
dynamic structures
what are microfilaments composed of
globular actin monomer
MF: actin monomers bind
ATP
MF: actin monomers assemble to form
a filament
MF: 2 parallel _____ twist around each other to form a ___________
protofilaments
right handed helix
MF: actin subunits assemble _____ to ____ and generate filaments with a distinct ______
head to tail
polarity
MF: filaments “grow” from the _____ end
plus
MF: actin filaments are ________ and ______
relatively flexible and easily bent
MF: in living cells, accessory proteins crosslink and bundle MFs together to create __________ actin structures much _____ than individual MFs
large-scale
stronger
localization of MFs
-MFs are often concentrated near the cell periphery
-Actin filaments are also observed running the length of cells
main roles of MFs determine the ___________ and to facilitate__________
shape of the cell’s surface
whole cell locomotion
Microtubules (MT) made up of:
-globular tubulin subunits
-tubulin monomers bind GTP
-alpha nad beta tubulin monomers form tubulin heterodimers
-protofilament is composed of alternating alpha and beta tubulin
MTs: cylinder structure
13 protofilaments build the MT cylinder
Cylinder is long and hollow
MT has an associated _______ .
polarity
- subunits point in one direction
-protofilaments are parallel
-growing end =plus end
the multiple contacts in the MT lattice make MT __________
stiff and difficult to bend
MT localization:
-nucleation occurs at the MTOC
-MTOC anchors and protects minus end of growing filament
-in animal cells, centrosome is near the nucleus
-from the MTOC, the MTs emanate in a star like conformation often out to the cell periphery
the main role of MTs:
determine the positions of membrane enclosed organelles and to direct intracellular transport
IFs structure:
-heterogenous family of rope-like filaments
-assembled from distinct subunits (inc. keratins, neurofilaments, vimentin-like proteins, lamins)
-does not contain an associated nucleotide (NTP)
IFs: are made by:
-elongated alpha helical monomeric subunits dimerize and then associate to form staggered tetrameric subunits
-tetramers pack together to form protofilament
-filament formed from 8 parallel protofilaments
-non-polar
-easily bent but hard to break
IFs localization:
-IFs provide strength to cells and tissues
-in general, IFs are prominent in cells that are subject to mechanical stress
main role of IFs
provide mechanical strength and provide shape to cells and help resist pulling forces
_______ are a diverse population of proteins that bind to filaments or subunits to control filament behavior and organization
accessory proteins
accessory proteins can:
1 . crosslink or bundle filaments
2. nucleate filament polymerization
3. cap and block polymerization
4. sever filaments
motor proteins overview:
-unique cytoskeleton binding protein -function to move molecules and membrane enclosed organelles throughout cell
-can be used to generate force required to move filaments
molecular motors convert energy from _____ into _______ to _______
ATP hydrolysis
mechanical force
‘walk’ along MF and MT filaments
what are the 3 major families of motor proteins:
- myosin
- kinesin
- dynein
what is the associated filament for myosin
microfilaments (actin)
what is the associated filament for kinesin ?
microtubules
what is the associated filament for dynein
microtubules
what direction does myosin go
POS
what direction does kinesin go
POS
what direction does dynein go
NEG
motor proteins associate with filament tracks via what?
a “head” region, or motor domain
what does the head region of motor proteins do?
binds and hydrolyzes ATP
what does the tail region do of motor proteins
contains the binding site for cargo
which molecular motor is the largest and fastest
dynein
in kinesin, the binding/hydrolysis of ATP by the head/motor domains _________
changes the conformation of the protein which allows kinesin to “walk” or “step” down the MT towards the plus end
for dynein, nucleotide hydrolysis is coupled to _____
MT bindning and unbinding as well to a force-generating conformational change
dynein’s power stroke is driven by the _______
binding and hydrolysis of ATP which causes the motor head to rotate relative to the tail
what is the function of kinesins
-bring cargo to the periphery of the cell
-organelle positioning
-axonal transport
-mitosis
what is the function of dyneins?
-bring cargo to the periphery of the cell
-cilia/flagella beating
-vesicle transport
-mitosis
clinical relevance of cytoskeleton
disruption of filament structure and dynamics is associated with many disease pathologies
example of mutation in actin binding protein, dystophin
canine x lined muscular dystrophy
mutations in a range of actin/actin associated proteins are observed in patients with
cardiomyopathy
_____ binds and stabilizes microtubules
taxol
cilia structure
9 sets of MT doublets and center pair of MTs (9+2)
dynein motors
microfilaments are made of what subunits
actin
microtubules are made of what subunit
tubulin
intermediate filaments are made of what
keratin, neurofilaments, vimentin, lamin
