Lecture 19: Cytoskeleton Flashcards
Types of Cytoskeletal Elements from smallest to largest
-actin filaments (smallest)
-intermediate filaments
-microtubules (largest)
actin filaments (descr.)
8-9 nm diameters; twisted tow-stranded structure
intermediate filaments (descr.)
10 nm rope
microtubules (descr.)
hollow, tube-like structures; 24 nm diameter
action microfilaments are concentrated ______
in cortex beneath PM
microtubules are attached to ____
MTOC (centrosome)
intermediate filaments are structural elements that ______
provide overall structure for cells
Microtubules are tracks in cells that ____
allows for transport of vesicles
Actin propel ____
some movement within cells
Function of cell junctions
for cells to communicate with each other
Intermediate filaments are found in ______ but not _____
nearly all animals
plants and fungi
Intermediate filaments (IF) are associated with ____ (4)
nucleus
ER
mitochondria
PM
Intermediate filaments are abundant in what type of cells?
epithelial and neuronal cells
Most ubiquitous intermediate filaments are _____, found exclusively in the _____
lamins
nucleus
IF are important for the ____ and _____ of organelles
structure and positioning
Vimentin-like IF is in what type of cells?
neuronal cells
Keratin IF is in what type of cells?
epithelial cells
structure of IF
central coiled-coil a-helical “rod” domain, flanked by non-a-helical N-terminal head and C-terminal tail domains
vimentin and desmin are IF that _______ filaments
homopolymeric
keratins are IF that _______ filaments
obligate heteropolymers
coiled-coil domains had been described for the first time in ____
keratin
IF proteins are typically _____ and are substrates of _______
phosphorylated
caspases during apoptosis
During apoptosis, IF are targeted by ____ because _____ (saying)
caspases
if you are collapsing a tent, you need to break all the rods holding it up
IF (monomer -> dimer –> tetramer –> filament)
monomer: coil has directionality with NH2 and COOH ends
coiled-coil dimer: 2 monomers coiled around each other; has directionality with NH2 and COOH ends
tetramer: staggered two coiled-coil dimers; NH2 end of one dimer interacts with COOH end of other dimer: antiparallel- lost directionality
filament: lateral association of 8 tetramers; no directionality
Directionality of IF
no directionality
nuclear lamina is where?
just inside the inner nuclear membrane
nuclear lamina is what? functions?
complex meshwork
nuclear lamina functions
maintenance of nuclear shape
transcriptional regulation
nuclear pore positioning and function
heterochromatin organization
the nuclear lamina plays a part in transcriptional regulation by binding to _____ such as ____
transcription factors
Rb and SREBP-1
Hutchinson-Gilford Progeria is caused mutation ____? in exon ___? effect on translated amino acid sequence? effect on protein structure?
C1824 to T1824
exon 11
no effect on a.a; still Gly 608
creates cryptic donor splicing site which removes 50 a.a from Lamin A tail
Hutchinson-Gilford Progeria effect on nuclear structure? phenotype?
altered nucleus
affected people have very short lifespan
Microtubules are ___ than intermediate filaments.
stiffer
Microtubules are polymers of ____, arranged in a
________ in diameter
globular tubulin subunits
cylindrical tube measuring 25 nm
Microtubules (MT) come in two forms
stable and short-lived
short-lived MT are involved in the formation of ____
the spindle apparatus during mitosis
MT can can oscillate between ______ enabling cells to quickly assemble and disassemble microtubules
shortening and growing phases,
MT are built from _____
a- and b-tubulin heterodimers
_______ serves to nucleate polymerization of MT (de novo formation of MTs) in ____
g-tubulin
MTOC
Microtubule polymerization involves the binding of
______
GTP-loaded b-tubulin in a complex with GTP-loaded a-tubulin
After GTP-loaded b-tubulin in a complex with GTP-loaded a-tubulin is added to tubule, _____
b-tubulin then undergoes GTP hydrolysis (like when it is in the middle)
polarity of MTs?
there is a polarity of MTs (polus and minus end)
+ end = elongations ______
- end = elongations ____
happens faster
happen slower
MT: when tubulin exists as subunits, they tend to be ____ then when they become part of MT, ____
in GTP-bound form
hydrolysis happens
MT grow on ____ which are recognized by _____
+ ends
the GTP-loaded B-tubulin
GTP cap of MT(def.)
enrichment of GTP-loaded B-tubulin on + end
catastrophe of MT (def.) + leads to ___
random loss of GTP cap; destruction of MT + end
rapid shrinkage of MT
rescue of MT (def.) + leads to _____
regain of GTP cap
rapid growth with GTP-capped end
nocodazole is a drug that _____
interferes with MT formation; causes MT depolymerization
microtubules grow and shrink in a _____manner; has ____
GTP-dependent
dynamic instability
_____is the most abundant protein in cells. In muscle cells, comprises ______, in non-muscle cells makes up _____.
Actin
10% of weight of total protein
1-5% of total protein
Actin concentration in cell
0.1-0.5 mM
Actin exists as a ____ and _____
globular monomer called G-actin
filamentous polymer called F-actin
each actin molecule can bind to ______ through ____
ADP or ATP
a magnesium ion
Most common forms of actin
ATP-G-actin
ADP-F-actin
actin is ___-dependent (as a cofactor)
ATP
Actin polymerization method
1)G-action comes together - nucleation
2) G-actin nucleus elongates and becomes F-actin- elongation
3) Steady state
___ is a common loading control for cells in the lab
actin
Actin polymerization requires nucleus of _____
polymerized ATP-G-actin
actin fiber aka ____
F-actin
During elongation, F-actin _____ATP to become ______
hydrolyzes
ADP-bound F-actin
actin formation phases
1) nucleation (lag phase)
2) elongation (growth phase)
3) steady state (equilibrium phase)
nucleation (lag phase)
G actin subunits form oligomers
elongation (growth phase)
growing actin filaments
steady state (equilibrium phase)
actin filaments with subunits coming on and off; still dynamic
Critical concentration (def.)
concentration where there is no net change in polymer
Actin formation + thermodynamics
it’s favored to have longer action filaments
actin polymerization is ___ through the mechanism called ____
directional
treadmilling
actin polymerization is demonstrated with _____
a capping protein that does not allow incorporation of G-actin monomers at either the + or the - end.
actin’s polarity is achieved by the ____
lower conc (lower critical concentration) required for incorporation into the + end
above the critical concentration
elongation (adding G-actin)
below the critical concentration
removing G-actin
actin-interfering drugs are also ___ becuase____
anti-cancer drugs because these cells require many cell divisions
ARPs are ____
actin related proteins
ARPs exhibit about ____
50% sequence simialrity with action
ARP2/3 complex contains how many proteins?
7 proteins
ARP2/3 complex function
ARP2/3 simulates actin growth and results in a branch point
ATP hydrolysis of ARP2 leads to ____
the debranching of ARP2
ATP-hydrolysis deficient mutant of ARP2 (arp2H161A) blocks _____
debranching of actin y-branches
blocks endocytosis
ARP2/3 is controlled by ___
Rho family of GTPases
GEF action
GDP-bound to GTP-bound
Guanine nucleotide exchange factors
GAP action
GTP-bound to GDP-bound; gas pedal
GTPase-activating protein
GDI action
keeps it GDP-bound; brake
Guanosine dissociation inhibitors
GDP-bound of Rho
inactivated form
GTP-bound of Rho
activated form; effector;engine
T17N mutants of Rho
permanently bound to GDP, also called kinase-dead
non-active mutant
Q61L mutants of Rho
permanently bound to GTP, also called
dominant active (ENGINE ALWAYS ON)
always active mutant
stress fiber arrangement of actin
contractile bundle
cell cortex arrangement of actin
branched and unbranched filament network
lamellipodium arrangement of actin
branched network
filopodium arrangement of actin
tight parallel bundle
Rho family members and different arrangements of actin
Cdc42 - filopodia
Rac - lamellipodia
Rho - stress fiber
NPF stands for _____
nucleation-promoting factors
NPF are regulated by _____ that ____
signal transduction pathways that coordinate actin polymerization in space and time
The activation of class I NPFs are by _____
Rho-family GTPases CDC42 and Rac.
2 important class I NPFs
WASP
WAVE
the NPF WASP is activated by ______
Cdc42
the NPF WAVE is activated by ______
Rac
The activation of NPFs is downstream of a signaling cascade based on _____
Rho and Cdc42/rac family GTPases and lipid second messengers
Binding of ___ and _____ to WASP, triggers the activation of ______ and dissociation from its _____
PI (4,5)P2 and GTP-loaded Cdc42
ARP2/3 complex
inhibitor WIP
Activated Rho (_____) binds to NRFs to induce ____
Cdc42 or Rac
interaction with Arp2/3
WASP stands for_____
Wiskott-Adrich Syndrome Protein
WASP pattern , when expressed from a transfected plasmid? This pattern______
spotty staining pattern
aligns with actin cables
Expression of CDC42-N17 (=T17N) effect of WASP pattern? conclusion?
disperses spotty staining pattern
Cdc42 interacts with WASP to form branched actin structure
WAVE stands for ____
Wiskott-Aldrich Verprolin-Homologous Protein
Overexpression of WASP and WAVE cause _____
abnormally many branching events, resulting in a “dispersal” of the actin cytoskeleton
WAVE location in neurons?
close to the neurite growth cone
WAVE-/- neurons have ____
shorter neurons
WAVE -/- mice show ____ affecting _____ and ____
mental retardation
spatial learning
memory retention
WAVE is co-immunoprecipitated with protein ____ which is implicated in ______
WRP
human mental retardation
The formation of____ structures are also crucial for cell movement
filopodia and lamellipodia
Spatial learning and memory retention require actin remodeling because _____
it enables neurons to form and retain neurite extensions
