14.4 Microtubule Motors and Movement

Question 1

what are the 2 protein motors involved in powering microtubule movement?

Answer 1

1. kinesins - move towards plus ends of microtubules
2. dyneins - move towards minus ends of microtubules

Question 2

compare and contrast the general structure of kinesins and dyneins

Answer 2

• both kinesins and dyneins have heavy and light chains
• only dyneins have intermediate chains

Question 3

motor movement of kinesins and dyneins is powered by ()

Answer 3

ATP

Question 4

how does ATP allow for kinesin/dynein movement along microtubules

Answer 4

interaction of motor protein globular head domains (motor domains) with ATP causes a conformation change in the head domains, thus allowing them to move along microtubules

Question 5

experiments (isolation of kinesin) found that in the presence of ATP, motor proteins (i.e. kinesins) ()

Answer 5

interact and release from microtubules

Question 6

how are kinesins and dyneins involved in cargo transport

Answer 6

• microtubules are usually oriented with their minus ends anchored at the centrosome and their plus ends extending toward the cell periphery
• kinesins usually bring cargo (usually vesicles/organelles) towards cell periphery, where as dyneins usually bring cargo towards the center of the cell

Question 7

cargo selection can be very specific → dyneins and kinesins recognize different microtubules by the ()

Answer 7

posttranslational modifications of tubulin

Question 8

which motor proteins are involved in position which membrane-bound organelles in the cell?

Answer 8

• kinesins play a role in positioning and pulling the ER towards cell periphery
• dyneins play a role in positioning the Golgi at the center of the cell

Question 9

the ER extends to the periphery of the cell through ()

Answer 9

association with microtubules

Question 10

() are microtubule-based projections of the plasma membrane that are found on almost all types of animal cells

Answer 10

cilia and flagella

Question 11

() act as antennae that sense a variety of extracellular signals as well as being responsible for movement

Answer 11

cilia

Question 12

some bacteria have (), but these are protein filaments projecting from the cell surface rather than microtubule-based projections

Answer 12

flagella

Question 13

() are found on most animal cells and are involved in sensing extracellular signals; they play an important role during development but have no motor function in adults

Answer 13

primary cilia

Question 14

() are responsible for movement (same with flagella) either across a surface or movement of fluid/mucus across cell surface (e.g. in epithelial cells)

Answer 14

motor cilia

Question 15

structures of cilia and flagella are similar; both have:

Answer 15

1. basal body - where the protrusion (i.e. cilia or flagella) extends from cell body
2. axoneme - actual protrusion of cell

Question 16

describe the structure of the basal body

Answer 16

• centriole containing 9 triplets of microtubules (triplet microtubules)
• derived from centrioles that have been transported to the plasma membrane
• serve to initiate the growth of axonemal microtubules as well as anchor cilia to the surface of the cell

Question 17

describe the general structure of an axoneme

Answer 17

contains 9 doublet microtubules (two from each of the triplets in the basal body extend into axoneme); contains a complete A tubule (13 protofilaments) and an incomplete B tubule (10-11 protofilaments)

Question 18

axonemes of motile cilia and flagella contain an additional () and () that are responsible for motility

Answer 18

1. central pair of microtubules
2. associated proteins

Question 19

in motor cilia and flagella, doublet microtubules are arranged in a ()

Answer 19

”9+2 pattern” → central pair is surrounded by 9 doublets

Question 20

in motor cilia and flagella, outer doublets are connected to the central pair by ()

Answer 20

radial spokes

Question 21

in motor cilia and flagella, outer doublets are connected to each other by links of a protein called ()

Answer 21

nexin

Question 22

what proteins/structures are present in motor cilia/flagella but not in primary cilia?

Answer 22

1. central pair of microtubules
2. radial spokes
3. nexin
4. dyneins

Question 23

in motor cilia and flagella, () → motor activity drives movement of cilia/flagella

Answer 23

dynein bases are attached at each A tubule; head groups attach to the B tubule of the adjacent microtubule doublet

Question 24

how do motor cilia/flagella bend?

Answer 24

• dynein motor heads move along B tubules (towards minus ends) → A tubule of one doublet slides towards the base of the adjacent B tubule
• because the doublets are linked and held in place by nexin, the doublets bend

Question 25

during mitosis, dynamic instability accelerates as a result of ()

Answer 25

increased microtubule growth and catastrophe rates

Question 26

microtubule array in interphase cells disassembles to form the () (responsible for separation of daughter chromosomes)

Answer 26

mitotic spindle

Question 27

restructuring of microtubule cytoskeleton is directed by duplication of (1) → forms 2 separate (2)

Answer 27

1. centrosome 2. microtubule organizing centers at opposite poles

Question 28

what are the 3 kinds of microtubules involved in the formation of the mitotic spindle

Answer 28

1. kinetochore microtubules 2. interpolar microtubules 3. astral microtubules

Question 29

microtubules that attach to the condensed chromosomes of mitotic cells at their centromeres

Answer 29

kinetochore microtubules

Question 30

microtubules that aren’t associated with chromosomes but are stabilized by overlapping with each other in the center of the cell

Answer 30

interpolar microtubules

Question 31

microtubules that extend outward from the centrosomes to the cell periphery; plus ends are anchored in cell cortex

Answer 31

astral microtubules

Question 32

how are duplicated chromosomes aligned at the metaphase plate

Answer 32

alignment of chromosomes is mediated by rapid growth of kinetochore microtubules and capture of their plus ends by kinetochores

Question 33

what happens during Anaphase A

Answer 33

1. chromosomes move towards the spindle poles along the kinetochore microtubules 2. kinetochore microtubules shorten as they are disassembled by kinesins (act as microtubule-depolymerizing enzymes)

Question 34

what happens in Anaphase B

Answer 34

1. both interpolar and astral microtubules contribute to chromosome movement by pushing the spindle poles apart 2. kinesins cross-linking interpolar microtubules move towards plus ends → causes overlap between interpolar microtubules to decrease and spindle pole to be pushed apart 3. dyneins anchored on the cell cortex pull the spindle poles apart by pulling them closer to the cell cortex; this is aided by the depolymerization of astral microtubules as the dyneins move towards their minus end