Cell Bio Chapter 16 Exam 3

Front 1

3 main types of major filaments

Back 1

actin, micrtubules, intermediate filaments

Front 2

function of actin filaments

Back 2

cytoplasmic streaming,
provide mechanical strength to a cell by forming a band under the plasma membrane
generte locomotion in cells

Front 3

functions of microtubules

Back 3

They determine the positions of
membrane-enclosed organelles and direct intracellular transport

Front 4

intermediate filaments provide

Back 4

mechanical strength
depend on lateral budnling and coiled coils

Front 5

tubulin actin molecules assemble

Back 5

head to tail to create polar filamentst

Front 6

tubulin is a

Back 6

heterodimer

Front 7

what is the rate limiting step in formation of a cytoskeleton polymer

Back 7

nucleation

Front 8

filament treadmilling and dynamic instabilty are

Back 8

consequences of nucleotide hydrolysis by tubulin and actin
as filament grows, elongation is faster than hydrolysis at the plus end and the terminal subunits are always in T form. at minus end its vice versa in d form

Front 9

treadmilling occurs

Back 9

at intermediate concentrations of free subunits

Front 10

actin molecules nucleate at the

Back 10

plasma membrane

Front 11

actin elongation is regulated by

Back 11

formins

Front 12

how are actin filaments organzed

Back 12

by crosslinking proteins

Front 13

A protein complex containing γ-tubulin nucleate

Back 13

microtubules

Front 14

Microtubules emanate from the

Back 14

centrosome in animal cells

Front 15

Stathmin binds to two tubulin heterodimers and

Back 15

prevents their addition to
the ends of microtubules.

Front 16

t/f the role of ATP hydolysis in actin polymerization is simlar to the role of GTP hydrlys

Back 16

true

Front 17

t/f in most animal cells, minus end directed microtuble motors deliver their cargo the peryphery of the cel

Back 17

flase

Front 18

t/f motor neyrons triffer action potentials in cell membanes that open voltage sensitve in t

Back 18

flase

Front 19

how does lateral association promote the subsequent rapid formation of a microtubule

Back 19

once first association has occured, th enext alpha beta dimer can bind much more readily because its stabilized by lateral and longitudnal contact

Front 20

how many alpha beta tubulin dimers are added to the ends of a microtubule each second

Back 20

54 per second

Front 21

how does a centrosome know when its found the center of the cell

Back 21

it nucleates a 3d array of microtubes that grow until they encounter an obstacle, the plasma membrane. dynamic nstability of microtubules plus equal pushing in each direction eventually lead it to the center. when alll oppositely directed microtubles are the same length, its in the center

Front 22

the concentration of actin in cells is 50-100 times grater han the critical condition ovserved for pure actine in a test tube. how is this possible

Back 22

in cells, most of the actin subunits are bound to thymosin, which locks actin in a form that cant hydrolyze its boudn atp and cant be added to filament ends. thymosin reduces concentration o ffree actin to around the critical cocenctraion. Advantage is that the cell can maintain a large pool of subunits for explosive growth at the sites and times of its choosng.

Front 23

what is a tubulin homolog in bacteria

Back 23

FTSZ

Front 24

intermediate filaments

Back 24

example: nucelar lamins
subunits are fibrous elongated, not globular

Front 25

ARP complex of actin grows from the

Back 25

negative end, allowing elongation at the positve end
proteins that play a role:Arp 2 and Arp3
works best when attached at a 70 degree angle

Front 26

formin

Back 26

dimer. Associates with the plus end. Binds to actin subunit and elongates filament only through the + end

Front 27

thymosin

Back 27

locks actin so that it cannot bind to the positve or negative end

Front 28

proflin

Back 28

associates with plasma membrane and recruits actin monomers
it binds to the site opposite of actin binding site

Front 29

tropomysosin

Back 29

stabilizes
has 7 actin filaments
filaments by binding simultaneously
to seven adjacent actin subunits in one protofilament This prevents
other proteins from binding to actin

Front 30

cofolin

Back 30

destabilizes by forcing a really tight twist

Front 31

Stathmin of microtubules

Back 31

binds the two heterodimers so they are not available for growth. When microtubules need to grow, phosphorylate stathmin and release microtubules

Front 32

dyneins

Back 32

family of minus end directed microtubules
2 tyoes:
cytoplasmic dyneins and axonemal dyneins
cytoplasmic found in eucaryotes for vesicle transportation

Front 33

t/f the structural polarity of all microtubules is taht alpha is exposed at one end and beta exposed at the other

Back 33

true

Front 34

t/f like actin filaments and microtubules, cytoplasmic intermediate filaments are found in all eurcaryotic cells

Back 34

false
only in metozoans

Front 35

what are the general functions of intermdiate filaments, acin, and microtubules

Back 35

intermediate filaments: mechanical stability
actin: determine cell shape and are required for locomotion
microtubules: direct intracellular transport and determine position of organelles

Front 36

why are humans strong if connections weak?

Back 36

large number of filaments so stress is spread out so their interaction strength will not be exceeded

Front 37

lag phase

Back 37

actin monomers assmeble into a nucleus for polumerization
B- is formation of a nucleas/rapid growth
C-equilibrium between rates of addition and release of actin

Front 38

why does a microtubule shrink

Back 38

it lost its GTP cap
if you add enough GTP subunits, you can stop shrinking

Front 39

what is GAP for beta tubulin

Back 39

tubulin itself, it accelerates GTP hydrolysis by the formation of intersubunit contacts during polymer- ization.

Front 40

few examples of the differences between bacteria and animal cells

Back 40

Animal cells are much larger, diversely shaped, and do not have a cell
wall. Cytoskeletal elements are required to provide mechanical strength
and shape in the absence of a cell wall.
Animal cells have internal organelles.
Animal cells, and all other eucaryotic cells, have a nucleus that is shaped
and held in place by intermediate filaments

Front 41

disulfide bonds do not form in cytosol of eucaryotic cells yet keratin intermediate filaments in skin are corsslinked by disulfide bonds. How can this be?

Back 41

these bonds form after the cell has died

Front 42

why are these drugs toxic to dividing cells?

Back 42

Cell division depends on ability of microtubules to polymerize and depolymerize. Taxol- treated cells are prevented from depolymerizing their existing microtubules, and thus cannot form a mitotic spindle. Colchicine-treated cells cannot polymerize new microtubules, and thus are also prevented from forming a mitotic spindle.

Front 43

is acrylamide toxicity mediated through its effects on neurofilaments?

Back 43

probably notIf the original hypothesis were correct, then acrylamide toxicity would have been expected to be absent in mice that are missing neurofila- ments.

Front 44

how does cofolin distinguish old from new

Back 44

older has more ADP actin