Histology Lecture 7: Cytoskeleton

Question 1

Actin Microfilaments

Answer 1

highly conserved among eukaryotes; 7 nm thick; up to 7 micrometers in length; organized into bundles and 3D networks; bind to specific transmembrane proteins either directly or indirectly (via catenins);

Question 2

What is roughly the length/width of a eukaryotic cell

Answer 2

7 micrometers

Question 3

First step in actin polymerization

Answer 3

nucleation

Question 4

the growing end of the actin microfilament

Answer 4

plus or barbed end

Question 5

actin microfilament; grows 5-10 times faster than the other end

Answer 5

barbed/plus/growing end

Question 6

where the rate of addition of new G-actin to actin filaments occurs more rapidly and at a lower concentration

Answer 6

barbed/plus/growing end

Question 7

slower growing end of the microfilament

Answer 7

minus/pointed end

Question 8

favored by low concentrations of G-actin

Answer 8

disassembly at plus/barbed/growing end

Question 9

the dynamic equilibrium between the minus end and the plus end that is favored by intermediate concentrations of G-actin

Answer 9

treadmilling

Question 10

favored by higher concentrations of G-actin

Answer 10

net addition at both ends, and therefore, growth of the actin filament

Question 11

the dynamic balance between the polymerizing and depolymerizing ends of F-actin

Answer 11

treadmilling

Question 12

bind to barbed ends of actin to block elongation

Answer 12

cytochalasins

Question 13

binds to actin filaments and prevents dissociation; prevents depolymerization by binding to actin filaments

Answer 13

phalloidin

Question 14

responsible for the diversity of function of actin filaments in different regions of the cell

Answer 14

actin-binding proteins

Question 15

actin binding protein that binds cortical cytoskeleton to the plasma membrane and is found in RBCs

Answer 15

spectrin

Question 16

actin binding protein that binds cortical cytoskeleton to the plasma membrane and is found in muscle cells; a defective version will lead to muscular dystrophy

Answer 16

dystrophin

Question 17

actin binding protein that cross-links microvilli; hold together the core of the microvillus [2 answers]

Answer 17

villin and fimbrin

Question 18

actin binding protein that cross links actin to the plasma membrane in microvilli

Answer 18

Calmodulin and Myosin I

Question 19

actin binding protein that forms the cap of the fast growing barbed ends of F actin and promotes the elongation of unbranched F-actin

Answer 19

Formin

Question 20

actin binding protein that regulates the assembly of unbranched actin in cell protrusions, such as the intestinal microvilli, while remaining attached to the end of the barbed end

Answer 20

Formin

Question 21

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

Answer 21

alpha-actinin

Question 22

actin binding protein that cross links actin at wide angles to form screen-like gels

Answer 22

Filamin

Question 23

actin binding protein that captures actin monomers and prevents actin monomers from being polymerized by sequestering pools of G-actin monomers within cells, thereby regulating treadmilling by keeping monomers out of circulation

Answer 23

Thymosin

Question 24

actin binding protein that suppresses nucleation of G-actin and promotes F-actin growth at the barbed end

Answer 24

Profilin

Question 25

actin binding protein that can favor the assembly of monomeric G-actin into filaments by facilitating the exchange of bound ADP for ATP

Answer 25

Profilin

Question 26

actin binding protein that destabilizes F-actin and caps actin filaments, preventing loss or addition of G-actin

Answer 26

Gelsolin

Question 27

actin binding protein that, in the presence of Calcium ion, will fragment actin filaments and remain bound to the barbed end, forming a cap that prevents further filament growth

Answer 27

Gelsolin

Question 28

actin binding protein that triggers depolymerization of ADP-bound actin at the minus end; also known as actin depolymerizing factor

Answer 28

Cofilin

Question 29

actin binding protein that initiates growth of G-actin from the sides of existing filament and causes branching; actin nucleating complex of 7 proteins; intiates the branch of F-actin

Answer 29

Arp2/3

Question 30

binds to G-actin and induces F-actin depolymerization

Answer 30

Latrunculins

Question 31

8-10 nm thick; abundant in cells subject to mechanical stress; provide tensile strength in cells; desmosomes and hemidesmosomes; central alpha-helical rod flanked by head and tail domains

Answer 31

intermediate filaments

Question 32

dimers associate in a staggered antiparallel fashion to form tetramers and lose polarity in the process; more stable than actin and do not demonstrate dynamic behaviour

Answer 32

intermediate filaments

Question 33

associated with other cytoskeletal elements to form a scaffolding that organizes the internal structure of the cell

Answer 33

intermediate filaments

Question 34

25 micrometers in diameter; alpha and beta tubulin monomers form tubulin dimers; protofilaments are longitudinal rows of tubulin dimers;

Answer 34

microtubules

Question 35

consist of 13 protofilaments arranged parallel to form a cyclinder with a hollow core; exhibit polarity (fast growing plus end and slow growin minus end)

Answer 35

microtubules

Question 36

1) two polypeptides form a coiled dimer 2) dimers associate in a staggered antiparallel fashion to form tetramers 3) tetramers assemble end to end to form protofilaments 4) eight protofilaments are wound together to form filaments

Answer 36

Intermediate Filament Assembly

Question 37

microtubules; grows more rapidly than minus end in the presence of low calcium ion concentrations

Answer 37

plus end

Question 38

end of a microtubule associated with tubulin dimers with GTP bound to the Beta-tubulin

Answer 38

growing end

Question 39

condition by which microtubule tubulin dimers are added more rapidly than GTP is hydrolyzed thereby favoring growth of the microtubule

Answer 39

high concentrations of tubulin-GTP

Question 40

condition by which GTP at the plus end is hydrolyze and dimers are lost, favoring depolymerization

Answer 40

low concentrations of tubulin-GTP

Question 41

the polymerization-to-depolymerization transition frequency

Answer 41

catastrophe

Question 42

the depolymerization-to-polymerization transition frequency

Answer 42

rescue

Question 43

inhibit microtubule polymerization; anti-cancer drug used in the treatment of Hodgkins lymphoma

Answer 43

Vinblastin

Question 44

stabilizes microtubules; anti-cancer drug used in the treatment of breast cancer

Answer 44

taxol

Question 45

mediates transport of cargo towards the plus end of a microtubule (anterograde transport)

Answer 45

kinesin

Question 46

mediates transport of cargo towards the minus end of a microtubule (retrograde transport)

Answer 46

cytoplasmic dynein

Question 47

motor protein with only one head (other three have 2 heads)

Answer 47

Myosin I

Question 48

motor protein whose head moves towards the minus end (other three move towards the plus end)

Answer 48

cytoplasmic dynein