Lecture 19: Cytoskeleton Flashcards by Tami Ojewole

Types of Cytoskeletal Elements from smallest to largest

-actin filaments (smallest)
-intermediate filaments
-microtubules (largest)

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actin filaments (descr.)

8-9 nm diameters; twisted tow-stranded structure

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intermediate filaments (descr.)

10 nm rope

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microtubules (descr.)

hollow, tube-like structures; 24 nm diameter

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action microfilaments are concentrated ______

in cortex beneath PM

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microtubules are attached to ____

MTOC (centrosome)

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intermediate filaments are structural elements that ______

provide overall structure for cells

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Microtubules are tracks in cells that ____

allows for transport of vesicles

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Actin propel ____

some movement within cells

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Function of cell junctions

for cells to communicate with each other

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Intermediate filaments are found in ______ but not _____

nearly all animals
plants and fungi

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Intermediate filaments (IF) are associated with ____ (4)

nucleus
ER
mitochondria
PM

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Intermediate filaments are abundant in what type of cells?

epithelial and neuronal cells

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Most ubiquitous intermediate filaments are _____, found exclusively in the _____

lamins
nucleus

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IF are important for the ____ and _____ of organelles

structure and positioning

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Vimentin-like IF is in what type of cells?

neuronal cells

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Keratin IF is in what type of cells?

epithelial cells

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structure of IF

central coiled-coil a-helical “rod” domain, flanked by non-a-helical N-terminal head and C-terminal tail domains

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vimentin and desmin are IF that _______ filaments

homopolymeric

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keratins are IF that _______ filaments

obligate heteropolymers

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coiled-coil domains had been described for the first time in ____

keratin

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IF proteins are typically _____ and are substrates of _______

phosphorylated
caspases during apoptosis

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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

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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

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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

Lecture 19: Cytoskeleton Flashcards

(111 cards)