Unit 6

Question 1

Actin filaments are approximately…..in diameter

Answer 1

7nm

Question 2

Actin exists in cells in two major forms called…

Answer 2

G actin and F actin

Question 3

ATP is hydrolyzed by actin…

Answer 3

after assembly but before disassembly

Question 4

The concentration of actin monomers at which the rate of polymerization into filaments equals the rate of deploymerization is called the …….concentration

Answer 4

critical

Question 5

Each monomer of actin binds one molecule of the nucleotide triphosphate…

Answer 5

ATP

Question 6

The phenomena that takes place at a concentration of free actin at the midpoint between the critcial concentrations of the barbed and pointed ends of an actin filament is called…

Answer 6

treadmilling

Question 7

Which drugs blocks the assembly of actin filaments?

Answer 7

cytochalasin

Question 8

Actin filaments are stabilised by…

Answer 8

tropomyosin

Question 9

Branching of actin filaments can be initiated by…

Answer 9

Arp2/3

Question 10

Actin filaments are bound into bundles of parallel filaments by the proteins…

Answer 10

a-actinin and fimbrin

Question 11

Short actin filaments bind to tetramers of which protein to form the cytoskelton of erythrocytes…

Answer 11

spectrin

Question 12

Duchenne’s muscular dystrophy is characterised by…

Answer 12

a. X-chromosomal inheritance
b. childhood onset
c. abnormal dystrophin function

Question 13

Actin filaments are anchored at junctions called…

Answer 13

adheres junctions

Question 14

Which movement is not based on actin-myosin interactions?

Answer 14

chromosome movement during anaphase A

Question 15

During muscle contraction, the A band…

Answer 15

stays the same width and the I bands and H zone shorten

Question 16

The barbed (fast growing) end of actin filament is located in muscle…

Answer 16

at the Z disc

Question 17

Myosin ………..is present in muscle sarcomeres

Answer 17

II

Question 18

Intermediate filaments are typically ………in diameter

Answer 18

8-11nm

Question 19

Intermediate filaments function in…

Answer 19

providing mechanical strength for cells

Question 20

The intermediate filaments in the nucleus are made of…

Answer 20

lamins

Question 21

The desmin filaments in muscle cells connect…

Answer 21

Z lines of adjacent myofibrils

Question 22

Keratin filaments are found in what cell types?

Answer 22

Epithelial cells

Question 23

Vimentin is the major intermediate filament protein of ……. cells

Answer 23

fibroblast

Question 24

Which is not an intermediate filament protein?

Answer 24

Fibronectin

Question 25

Keratin filaments are anchored to junctions called...

Answer 25

desmosomes

Question 26

Which of the following is a protein that can link intermediate filaments with actin filaments and microtubules?

Answer 26

Plectin

Question 27

Expression of a shortened skin keratin gene in place of the normal keratin gene in transgenic mice resulted in a phenotype in which mice had...

Answer 27

fragile, easily blistered skin

Question 28

Lou Gebrig's disease (ALS) can result from a mutation in the gene for the intermediate filament protein...

Answer 28

neurofilament protein

Question 29

Microtubules are typically ..........in diameter

Answer 29

25 nm

Question 30

The evolutionary ancestor of eukaryotic tubules appears to be a protein similar to the bacterial protein...

Answer 30

FtsZ

Question 31

Microtubules are assembled from...

Answer 31

dimers of alpha and beta tubulin

Question 32

Which nucleotide triphosphate is hydrolyzed during a cycle of microtubule assembly and disassembly?

Answer 32

GTP

Question 33

The proteins Rab, Ran and tubulin are all...

Answer 33

G proteins, regulated by bound GTP or GDP

Question 34

When does the GTP bound to beta-tubulin hydrolyse to GDP and Pi?

Answer 34

Following polymerisation but before depolymerization

Question 35

The microtubule behaviour in which tubular adds at the plus end, fluxes through a constant length microtuble and comes off the minus end is called...

Answer 35

treadmilling

Question 36

The microtubule behaviour in which some microtubules are rapidly deploymerizing and some are growing is called...

Answer 36

dynamic instability

Question 37

Both colchicine and colcemod...

Answer 37

block microtubule assembly by binding to free tubulin

Question 38

The anticancer drug taxol acts to...

Answer 38

stabile microtubules and thus inhibit disassembly

Question 39

The major microtubule organising centre in most animal cells is the...

Answer 39

centrosome

Question 40

At the end of interphase, the part of the microtubule farthest from the centrosome is the ............ end

Answer 40

plus

Question 41

The role of the centrosome is to...

Answer 41

initiate microtubule growth

Question 42

Rings of the protein .......... in the pericentriolar material nucleate microtubule assembly

Answer 42

beta- tubulin

Question 43

Microtubules are not involved in...

Answer 43

cytokinesis of animal cells

Question 44

Kinesin 1 is a motor protein molecule consisting of...

Answer 44

two heavy chain and two light chains

Question 45

The cargo carried by kinesin along microtubules binds to kenesin on which region?

Answer 45

tail

Question 46

What cell components are kinesins able to transport along microtubules?

Answer 46

a. membranous vesicles and mitochondria b. endoplasimic retriculum c. MRNAs

Question 47

Cytoplasmic dynein plays a key role in the positioning of which organelle?

Answer 47

Golgi apparatus

Question 48

A male patient at a medical clinic present with infertility due to non-motile sperm and an inability to clear mucus from his respiratory tract. Others tissue are normal. You suspect that these symptoms may be caused by mutant...

Answer 48

dynein

Question 49

In a cilium or flagellum, .............microtubules are arranged.........................

Answer 49

9 doublet; in a circle around a central pair of microtubules

Question 50

The basal bodies of cilia and flagella are similar in structure to (and can form from)...

Answer 50

centrioles

Question 51

Adjucent microtubule doublets in cilia and flagella produce a bending movement because...

Answer 51

nexin links between microtubule doublets convert a sliding movement into a bending movement

Question 52

The beating of cilia and flagella occurs by means of ......... based ................

Answer 52

dynein; microtubule sliding

Question 53

The microtubules that overlap in the centre of the mitotic spindle are called ....... microtubules

Answer 53

polar

Question 54

The drug taxol stabilizes so they cannot shorten. if taxol were added during anaphase of mitosis, what effect would you expect it to have anaphase movements?

Answer 54

it would stop anaphase A but not anaphase B