Cytoskeleton

Question 1

What are three kinds of protein structures that make up the cytoskeleton?

Answer 1

> microfilaments
intermediate filaments
microtubules.

Question 2

What are features of actin filaments?

Answer 2

highly conserved structure, filaments organize into bundles, bind to transmembrane proteins, exist as monomers (G-actin) or long chains (F-actin).

Question 3

What does G actin have a binding site for?

Answer 3

> ATP (binds tightly to G-actin)

Question 4

How many other monomers can a single actin monomer bind with?

Answer 4

2

Question 5

Do actin monomers display polarity?

Answer 5

yes

Question 6

What is nucleation?

Answer 6

> The first step of actin polymerization.

> A trimer is formed and additional actin monomers can then be added to either end.

Question 7

ATP-actin associates which end of the actin filament?

Answer 7

> the plus/barbed end

> ADP is made once actin binds here.

Question 8

What affects the rate of monomer addition to a growing filament?

Answer 8

the cytosolic concentration of actin monomers.

Question 9

Which end of the actin filament grows faster?

Answer 9

barbed end

Question 10

At what concentration do actin filaments disassemble?

Answer 10

low concentrations of G-actin

Question 11

What is treadmilling?

Answer 11

> intermediate concentrations of G-actin

AND

> a dynamic equilibrium of growth and recession at the barbed and pointed ends.

Question 12

What do high concentrations of G-actin favor?

Answer 12

higher concentrations of G-actin at both ends (e.g. growth)

Question 13

What do cytochalasins do?

Answer 13

bind to barbed ends and prevent more actin monomers from binding. They also prevent movement/cell division.

Question 14

What does phalloidin do?

Answer 14

> binds to actin filaments and prevents dissociation.

> can be labeled with fluorescent dyes to allow visualization of actin filaments

Question 15

What determines the diversity of functions of actin?

Answer 15

the actin-binding proteins, not actin itself.

Question 16

What are some actin binding proteins?

Answer 16

spectrin (RBC passage through capilliaries); dystrhophin (binds cytoskeleton to plasma membrane); villin/fimbrin (holds actin filaments together); calmodulin and myosin I (cross links actin to plasma membrane).

Question 17

What actin-binding proteins control treadmilling?

Answer 17

thymosin and profilin. Both prevent actin from being polymerized.

Question 18

What are intermediate filaments?

Answer 18

filaments that provide tensile strength in neurons and muscle, strengthen epithelial cells as desmosomes and hemidesmosomes, etc.

Question 19

What is the structure of intermediate filaments?

Answer 19

> monomer consisting of a central alpha-helical rod flanked by head and tail domains.

Question 20

How are intermediate filaments assembled?

Answer 20

two polypeptides form a dimer —-> dimers form tetramers —-> tetramers form protofilaments —-> 8 protofilaments form a filament.

Question 21

What are the functions of intermediate filaments?

Answer 21

> form cytoplasmic networks in cells

> associate with other cytoskeletal elements to form a scaffolding that organizes the internal structure of the cell.

Question 22

What are microtubules made of?

Answer 22

tubulin dimers; there is an alpha and beta subunit that make two separate helices.

Question 23

What is dynamic instability?

Answer 23

alternate phases of slow growth and rapid depolymerization. GDP is quickly released from the - end.

Question 24

What is colchine?

Answer 24

a drug that inhibits microtubule polymerization. It is used for cancer treatment.

Question 25

What is taxol?

Answer 25

an anti-cancer drug that stabilized molecules (prevents depolymerization).

Question 26

What are some functions of the cytoskeleton?

Answer 26

``` > cell movement > support and strength > phagocytosis > mitotic spindle formation > cytokinesis > changes in cell shape. > cell-to-cell and cell-to-extracellular matrix adherences ```

Question 27

What molecule travels from the minus end to plus end to deposit tubulin?

Answer 27

kinesin

Question 28

Which molecule carries cargo from the plus end to the minus end?

Answer 28

cytoplasmic dynein.

Question 29

Which myosin molecule is the only one with two heads?

Answer 29

myosin I

Question 30

What do the heads of kinesin and cytoplasmic dynein bind to?

Answer 30

microtubules

Question 31

What do the heads of myosin I and II bind to?

Answer 31

actin

Question 32

What do the tails of kinesin and cytoplasmic dynein bind to?

Answer 32

vesicles

Question 33

What do the tails of myosin I and II bind to?

Answer 33

the cell membrane (I) and myosin II (II).

Question 34

Is actin polymerization reversible?

Answer 34

> yes

Question 35

_____-actin dissociates more readily from filaments than _____-actin?

Answer 35

> ADP | > ATP

Question 36

**Actin fact**

Answer 36

> actin is a very common and very ubiquitous protein found in all cells, but in spite of the fact that it has pretty much the same structure in all cells, it is involved in a number of kinds of functions

Question 37

This is determined by the actin-binding proteins and not by actin itself?

Answer 37

> the diversity of function of actin filaments

Question 38

Spectrin (ABP)?

Answer 38

> found in RBCs | > binds cytoskeleton to plasma membrane

Question 39

Dystrophin (ABP)?

Answer 39

> binds cortical cytoskeleton to the plasma membrane

Question 40

Villin and Fimbrin (ABPs)?

Answer 40

> cross-link actin to plasma membrane in microvilli

Question 41

alpha-actinin (ABP)?

Answer 41

> cross-links stress fibers and connects actin to protein plasma membrane complex complexes

Question 42

Filamin (ABP)?

Answer 42

> cross-links actin at wide angles to form screen like gels

Question 43

Thymosin (actin-binding molecule/control treadmilling)

Answer 43

> captures actin monomers | > prevents monomers from being polymerized

Question 44

Profiln (actin-binding molecule/ control treadmilling)

Answer 44

> binds to actin monomers and prevents monomers form being polymerized > facilitates exchange of ADP for ATP----which favors polymerization > only ATP-actin monomers can be assembled into F-actin

Question 45

Gelsolin (actin-binding molecule/ control treadmilling)

Answer 45

> destabilizes F-actin and caps actin filaments, preventing loss and addition of G-actin > In presence of calcium ion, fragments actin filament and remains bound to plus (+) end

Question 46

Cofilin (actin-binding molecule/ control treadmilling)

Answer 46

> triggers depolymerization of ADP-bound actin at minus end

Question 47

Arp2/3 (actin-binding molecule/ control treadmilling)

Answer 47

> initiates growth of F-action from sides of existing filament---causes branching

Question 48

Phalloidin (actin-binding molecule/ control treadmilling)

Answer 48

> prevents depolymerization by binding to actin filaments

Question 49

Latrunculins (actin-binding molecule/ control treadmilling)

Answer 49

> binds to G-actin and induces F-actin depolymerization

Question 50

These intermediate filament types are associated with keratin?

Answer 50

> type I >>> acidic keratins > type II >>> neutral to basic keratins

Question 51

Microtubules consist of _____ protofilaments arranged parallel to form a cylinder with a hollow core?

Answer 51

> 13

Question 52

Protofilaments have a ______ growing plus (+) end and a _____ growing minus(-) end?

Answer 52

> fast | > slow

Question 53

What type of tubulin dimers associate with the growing end of microtubules?

Answer 53

> tubulin dimers with GTP bound to the beta-tubulin

Question 54

Low calcium ion concentration causes this end of the microtubule to grow faster than the other?

Answer 54

> Plus (+) end grows more rapidly than minus (-) end

Question 55

At high concentrations of _______, the dimers are added more rapidly than GTP is hydrolyzed, and the microtubule grows?

Answer 55

> tubulin-GTP

Question 56

Drugs that inhibit microtubule polymerization?

Answer 56

> colchicines > colcemid > vincristine > vinblastine

Question 57

This drug is used to treat Hodgkin's Lymphoma?

Answer 57

> vinblastine

Question 58

Drugs that stabilize microtubules?

Answer 58

> taxol

Question 59

This drug is used to treat breast cancer?

Answer 59

> taxol

Question 60

How do drugs such as colchicine work to prevent polymerization of microtubules?

Answer 60

> by binding to the tubulin dimers and preventing their assembly into microtubules

Question 61

How do drugs such as taxol work to stabilize microtubules?

Answer 61

> binds to microtubules preventing their depolymerization > taxol disrupts mitosis by affecting the dynamic assembly of the mitotic spindle. > antimitotic drugs bind to reverse sites on tubulin, and

Question 62

What mediates the anterograde transport of cargos along microtubule?

Answer 62

> kinesin

Question 63

What mediates the anterograde transport of cargos along microtubules?

Answer 63

> cytoplasmic dynein

Question 64

This may provide a mechanism for the transport of multiple cargos along microtubules?

Answer 64

> raft protein complex