Cytoskeleton Regulation

Question 1

MTs nucleate at the

Answer 1

Microtubule-organizing centre (MTOC)

Question 2

Microtubules are nucleated from their _________ ends with the ______ end growing outward from the MTOC

Answer 2

minus, plus

Question 3

_______ makes up the first part of the 13 part ring structure

Answer 3

MTOC

Question 4

True of false: MTOC allows for skipping of the lag step

Answer 4

True (allows for first tubulin dimers to be added)

Question 5

What happens if we mutate or remove the gamma tubulin from a cell

Answer 5

MTOC formation is extremely slow and less organized

Question 6

What direction does MT grow in

Answer 6

in most cases, minus end is stabilized and plus end is growing or shrinking, UNLESS minus end is not bound by MTOC

Question 7

Alpha is always toward the _____ _____ and beta toward the _______/_______ end

Answer 7

gamma tubulin, plus/growing end

Question 8

Most animal cells have a single well-defined MTOC called the _________ located near the _______

Answer 8

centrosome, nucleus

Question 9

_________ emanate from the centrosome in animal cells

Answer 9

microtubules

Question 10

The cytoplasmic microtubules emanate in what kind of formation

Answer 10

Star-like

Question 11

A centrosome is composed of a fibrous matrix that contains _____copies of γ-tubulin.

Answer 11

50

Question 12

What end is anchored and stabilized at the MTOC

Answer 12

minus end

Question 13

What cells and MTs do not always need to start at an MTOC

Answer 13

highly polarized cells, more stable MT’s

Question 14

Embedded in the centrosome is a pair of structures called ________ arranged at right angles to each other.

Answer 14

centrioles

Question 15

When do centrioles duplicate and when do they move to opposite poles of nucleus

Answer 15

Duplicate during cell division, move to opposite poles when mitosis begins

Question 16

“Highway of the cell”

Answer 16

Microtubules

Question 17

Nucleating sites

Answer 17

gamma-tubulin ring complexes

Question 18

Centrioles are surrounded by a

Answer 18

centrosome matrix

Question 19

Tubulin rings are capable of

Answer 19

polymerizing MTs

Question 20

MT aster

Answer 20

MTOC with plus end growing outwards from centrosome and minus end anchored and stabalized

Question 21

In animal cells, the astral configuration, with plus ends pointing out, acts as a device to

Answer 21

survey the outlying regions of the cell to position the centrosome at its center

Question 22

Where is the cis-golgi network found

Answer 22

right near nucleus

Question 23

Are MTOC found in differentiated cells (ex. epithelial cells that from cell-cell junctions, become highly polarized)

Answer 23

no

Question 24

Actin filaments are often nucleated at the

Answer 24

plasma membrane

Question 25

In contrast to microtubule nucleation, actin nucleation occurs most frequently at or near the _______ _______

Answer 25

plasma membrane

Question 25

Actin nucleation can be catalyzed by 2 different regulated factors

Answer 25

-ARP complex -Formins

Question 26

What gives proper shape to nucleate actin monomers (branched)

Answer 26

Orientation of ARP2 and 3 proteins, (fit into ARP complex and starts to grow)

Question 27

Filament nucleation by ARP occurs at __________ angles

Answer 27

70 degree angles

Question 28

Where does ARP complex bind on polymer of straight actin

Answer 28

Middle

Question 29

What type of actin is present at the growing tip of actin polymer

Answer 29

ATP

Question 30

Does ARP complex have greater affinity for ADP or ATP bound actin

Answer 30

ADP, (binds to middle where ADP is found)

Question 31

many large-scale actin structures are made up of parallel bundles of unbranched actin filaments nucleated by the

Answer 31

formins

Question 32

A family of dimeric proteins that have a binding site for monomeric actin

Answer 32

Formin

Question 33

As the nucleated filament grows, formin remains associated with the rapidly growing _____ end

Answer 33

plus

Question 34

Difference between formin and ARP

Answer 34

Formin associated with the plus end or nucleated filament, ARP is bound ro the minus end

Question 35

Lampelopodia made up of

Answer 35

Branched actin

Question 36

Filopodia made up of

Answer 36

Fillamentous actin

Question 37

In most vertebrate cells, approximately ____ of actin is in filaments and _____ is soluble.

Answer 37

50%, 50%

Question 38

Specialized proteins such as ________ prevent actin nucleation by binding to monomeric actin

Answer 38

thymosin

Question 39

How is "locked“ actin recruited for polymerization? - what does it depend on

Answer 39

Another monomeric binding protein called profilin

Question 40

What does profilin do

Answer 40

binds to actin at the face that normally binds the minus end, promoting the attachment of the monomer to a free growing plus end.

Question 41

GO REVIEW FORMIN

Answer 41

oh ya

Question 42

Profilin is localized where and binds to what

Answer 42

localized at the cytosolic face of PM and binds to phospholipids awaiting activation by extracellular signals

Question 43

intracellular mechanisms that regulate profilin activity

Answer 43

profilin phosphorylation and profilin binding to inositol phospholipids

Question 44

How does extraceullular signal (RTK activation) affect profilin

Answer 44

Profilin is released (it is bound to PM) and oes to "unlock" actin making it available for polymerization

Question 45

What acts as staging areas for addition of actin to the growing plus end of the actin filament (where formin is bound)

Answer 45

formin whiskers

Question 46

the cell sequesters unpolymerized tubulin subunits through the

Answer 46

stathmins

Question 47

What do stathmins do

Answer 47

-bind to two tubulin heterodimers preventing their addition onto growing filaments -phosphorylation to release tubulin and enhance polymerization

Question 48

Cancer cells frequently overexpress ______ resulting in an increased rate of microtubules turnover

Answer 48

Stathmins

Question 49

Severing proteins regulate the _______ and ________ behaviour of actin filaments

Answer 49

length, kinetic

Question 50

How does severing existing long filaments into smaller filaments affect the assembly of new filaments

Answer 50

Severing existing long filaments into smaller filaments accelerates the assembly of new filaments by exposing more plus ends

Question 51

What happens if you sever a filament in the center

Answer 51

you do not have the ATP (or GTP) cap anymore and you will have catastrophe right away

Question 52

What does katanin do (general)

Answer 52

Breaks 13 longitudinal bonds to sever a microtubule

Question 53

How does katanin break bonds

Answer 53

Katanin hydrolyzes ATP to perform this task and is directed to the centrosome where it releases microtubules directly from the centrosome

Question 54

Proteins that bind along the sides of filaments can either _______ or ________ them

Answer 54

stabalize, destabalize

Question 55

_________ are prominant in neurons and stabalize microtubules

Answer 55

MAPs (such as MAP2 and tau)

Question 56

Tau proteins with alzheimer's disease

Answer 56

hyperphosphorylation of Tau proteins, cannot stabalize MTs (neurofibrillary tangles)

Question 57

Dementia associated with Alzheimer's tau proteins

Answer 57

Impaired communication between neurons because the MT is not able to maintain a stable connection, cannot maintain the synapses needed for communication

Question 58

Where is Tau found

Answer 58

In the axon

Question 59

The MTs in the dendrites have a larger space between them when compared to the MTs in the axon.

Answer 59

Tau has both N an C terminals bound to one MT, stabalizes and creates a short tail (short space)-DENDRITE MAP2 binds two diferent MTs, creates a long tail (larger space) -AXON

Question 60

Actin filaments are stabilized by the binding of __________

Answer 60

tropomyosin

Question 61

what does cofilin do and how

Answer 61

destabalizes actin filaments by binding and forcing filaments to twist more tightly.

Question 62

What does cofilin bind to

Answer 62

preferentially binds to old ADP-containing filaments

Question 63

What does tropomyosin do in terms of cofilin

Answer 63

protects actin filaments from cofilin

Question 64

concentrations of proteins when binding along side a filament vs to a filament

Answer 64

along side- high concentrations to-low concentrations

Question 65

Filaggrin

Answer 65

bundles keratin filaments in the outer layer of the skin to give them toughness

Question 66

Plectin

Answer 66

cross-links intermediate filaments to microtubules and actin filament bundles

Question 67

Mutations in gene for plectin

Answer 67

cause a disease in humans that combines epidermis bullosa, muscular dystrophy, and neurodegeneration. called Epidermolysis bullosa simplex with muscular dystrophy (EBS-MD)

Question 68

________ and _______ cross-link actin into parallel bundles

Answer 68

Villin, fimbrin

Question 69

What forms the core of a microvillus

Answer 69

A bundle of parallel actin filaments cross-linked by the actin-bundling proteins villin and fimbrin

Question 70

web-forming/stabalizing proteins

Answer 70

filamins and spectrins

Question 71

What protein is lacking with some types of cancer cells

Answer 71

filamin

Question 72

Spectrins

Answer 72

-allow red blood cells to spring back to original shape after squeezing through a blood vessel -Provide flexible stiffness to most other types of vertebrate cell

Question 73

How are the gamma-tubulin ring complex and the ARP complex similar

Answer 73

Similarities: -both bind to and stabalize the minus end of a cytoskeleton element and promote nucleation

Question 74

How are the gamma-tubulin ring complex and the ARP complex different

Answer 74

Diferences: -ARP is associated with branched actin given it interacts with 'older' actin filaments at a 70 degree angle, gamma tubulin builds microtubules which are not branched