Cell Bio Lecture 14

filament types of the cell

microfilaments, microtubules, intermediate filaments

microfilaments subunit

actin

microtubules subunit

alpha beta tubulin dimer

intermediate filaments subunit

various

what controls the regulation of cytoskeletal function

signals

what separates apical and basolateral plasma membrane in epithelial cells

tight junctions

what provides support in the apical microvilli of epithelial cells

actin microfilaments

what do microtubules do in epithelial cells

allow for direction flow of vesicles

what structurally reinforces the morphology of epithelial cells

intermediate filaments

in a migrating cell, where is the leading edge oriented

direction of locomotion

examples of actin microfilament based structures

invadopodium, filopodia, leading edge, phagocytosis, contractile ring

what is the structure of monomeric G actin

ATPase

name for actin monomer

G actin

eukaryotic actin is related to…

bacterial MreB

actins from amoebae and animal actins are…

80% identical

how many different actin genes in humans

6

actin makes up what percentage of total protein mass in cells

1-5%

concentration of protein mass actin makes up in microvilli

5mM

how many subdomains in the central cleft of g actin

4

where does ATP/ADP bind in g actin

bottom of cleft

what is an F actin filament

polymerized actin monomers, microfilament

shape of F actin filament

helical

ATP binding cleft of every subunit is oriented how in microfilaments

toward the same end

negative end of microfilaments

exposed binding cleft

positive end microfilaments

buried end

microfilaments exposed binding cleft

negative

microfilaments buried end

positive

what are the three phases of g actin polymerization into f actin filaments

nucleation, elongation, steady state

what occurs during nucleation stage of G actin polymerization

formation of 3 ATP G actin seed

what happens during elongation phase of g actin polymerization

actin subunits assemble on each end of filament

what happens during steady state phase of g actin polymerization

g actin monomers exchange w subunits at filament ends, but length stays the same

which end of actin do subunits assemble faster

positive

how much faster do actin subunits assemble at positive end than negative end

10X

ADP g actin disassembly rates at both ends of actin are…

similar

what is steady state (regions of ATP, ADPPi, and ADP)

actin assembly at positive end is faster than hydrolysis, causes short region of ATP, regions of ADP Pi actin, and ADP actin toward negative end

what is actin filament treadmilling

ATP g actin assembles at positive end, ADP g actin disassembles at negative end, so subunits treadmill from positive to negative

what blocks assembly and disassembly at actin filament ends

capping proteins

what is CapZ

capping protein that blocks positive ends of actin

what is tropomodulin

capping protein that stabilizes filaments by blocking negative ends

what end does CapZ block in actin

positive

what end does tropomodulin block in actin

negativw

what does formin do in actin filaments

nucleates actin assembly

what does Arp2/3 complex do in actin filaments

nucleates branched filaments

nucleation promoting factors become available due to…

signaling pathways

Arp2/3 and formin are types of

nucleation promoting factor

what drives internalized endocytic vesicles away from PM

Arp2/3 dependent actin assembly

Arp2/3 dependent actin assembly drives what

internalized endocytic vesicles away from PM

what induces changes in the actin cytoskeleton

small GTPases

Cdc42 GTP leads to formation of…

filopodia

RacGTP leads to formation of

lamellipodia

RhoGTP leads to formation of

stress fibers and contraction

Cdc42 is activated at which end of the cell

front

Cdc42 activation promotes what where?

Rac activity in leading edge

what does Rac activate and where?

Rho at the back of the cell

what is the Rac activity in the leading edge (which protein)

Arp2/3 dependent actin polymerization

what does Rho activate

formin dependent stress fibers, myosin 2 dependent contraction

what does active Rho inhibit, and what does this prevent

Rac activation, leading edge structures at rear of cell

what is a tubulin dimer made of

alpha tubulin and beta tubulin monomers

alpha tubulin GTP activity

GTP is never hydrolyzed and non exchangeable

beta tubulin GTP activity

GDP exchangeable with GTP

tubulin dimers are aligned…

end to end in the same orientation into protofilaments

protofilaments pack…

side by side with same subunit polarity to form microtubule

what provides structural polarity of microtubule

dimer alignment

subunits added preferentially to which end of a microtubule

positive end

what end are beta tubulins exposed in microtubulins

positive

microtubules can form…

singles, doublets, and triplets

single microtubule location and function

cytoplasm, intracellular highways

doublet microtubule location and fucntion

cilia and flagella, cell surface antennae and motored extensions

triplet microtubules location and function

basal bodies and centrioles, microtubule organizing centers

what does the centrosome spawn in cells

polar microtubules

the centrosome is a type of…

microtubule organizing centers

what end of microtubules is pointing away from centrosome

positive end

what causes nucleation of microtubules

gamma tubulin ring complex

what causes branching of microtubules

augmin

shortened version of gamma tubulin ring complex

gamma TuRC

what does dynamic instability depend on

presence or absence of GTP beta tubulin cap

catastrophe dynamic instability in microtubules

rate of GTP hydrolysis is greater than rate of GTP tubulin addition

in microtubule formation, rate of GTP hydrolysis is…

constant

rescue dynamic instability in microtubules

rate of GTP tubulin addition is greater than rate of GTP hydrolysis

what bundles microtubules together

microtubule associated proteins

microtubule spacing depends on…

length of MAP IDR

MAP stands for

microtubule associated proteins

Tau is what in MAP

IDR

Tau undergoes…

LLPS

mutant tau becomes

solid

how many intermediate filament genes does human genome have

70

how many subfamilies of intermediate filaments

5

intermediate filaments are assembled from…

subunit dimers

tetramer filament subunit structure

antiparallel, staggered, side by side aggregation of two identical dimers

protofibrils are made up of

end to end laterally associated tetramers

small to large units of intermediate filaments

tetramer, protofilament, protofibril, mature filament

mature filaments are made up of

four protofibrils with globular domains forming beaded clusters on surface

how are microtubules and intermediate filaments crosslinked together

plectin and intermediate filament associated proteins

width of actin

7-9 nm

width of microtubules

25nm

width of intermediate filaments

10 nm