Microtubules

Question 1

isoforms of tubulin

Answer 1

α tubulin, ß tubulin, gamma tubulin

Question 2

α tubulin

Answer 2

always bound to & never hydrolyzes GTP; GTP binding site is blocked by beta tubulin

Question 3

ß tubulin

Answer 3

can hydrolyze GTP

Question 4

gamma tubulin

Answer 4

part of nucleation

Question 5

building block of microtubules

Answer 5

αß tubulin dimer

Question 6

describe how a microtubule is formed

Answer 6

an individual protofilament (linear) is formed & laterally associates protofilaments to create cylindrical structure

Question 7

How do the plus and minus ends of microtubules differ?

Answer 7

”+” end has significantly lower critical concentration than “-“ end (preferential building at “+” end)
creates “treadmilling” effect

Question 8

describe “treadmilling” effect

Answer 8

preferential addition of tubulin at “+” end, & disassembly at “-“ end

Question 9

singlet

Answer 9

made of 13 porotofilaments; found in the cell body

Question 10

doublet

Answer 10

made of 23 protofilaments (13+10); found in cilia/flagella

Question 11

triplet

Answer 11

made of 33 protofilaments (13+10+10); found in basal body/centriole

Question 12

MTOC

Answer 12

microtubule organizing center

Question 13

MTOC types

Answer 13

centrosome & basal body

Question 14

centrosome

Answer 14

MTOC in center of every cell, attaches to - end of microtubule singlets and triplets

Question 15

basal body

Answer 15

MTOC found just inside cell body in cells with cilia/flagella, attaches to - end of microtubule doublets

Question 16

gamma-TURC complex

Answer 16

made of gamma tubulin & other proteins; functions as a nucleation site for microtubule formation

Question 17

dynamic instability

Answer 17

microtubules undergo regular cycles of growth and shrinkage; microtubules experience a growth phase until a “catastrophe” initiates the disassembly phase - continues until “rescue”; necessary for mitosis

Question 18

What proteins contribute to dynamic instability?

Answer 18

kinesin-13, stathmin, katanin

Question 19

kinesin-13

Answer 19

binds to dimers at the + end (uses energy), curves end of tubulin protofilament, removes GDP bound dimers

Question 20

stathmin

Answer 20

binds 2 dimers of curved protofilament & removes them

Question 21

katanin

Answer 21

severs microtubules

Question 22

What are kinesins and dyneins?

Answer 22

motor proteins

Question 23

kinesin

Answer 23

”+” end directed motor protein, head region binds/hydrolyzes ATP & walks “hand-over-hand” along microtubule (similar to myosin structure)

Question 24

dynein

Answer 24

”-“ end directed motor protein, large complex that includes dyanctin (which interacts with the microtubule), light & heavy chains, etc.

Question 25

microtubule structures in flagella

Answer 25

``` axomeme = central bundle nexin = connects outer doublets dynein = moves flagella by allowing central singlets to slide past one another, creating a whipping motion ```

Question 26

roles of microtubules in cell division or mitosis

Answer 26

capture, alignment, and movement of chromosomes

Question 27

kinetochore

Answer 27

structure where kinetochore microtubules attach to chromosome

Question 28

centromere

Answer 28

structure where sister chromatids attach to each other

Question 29

classes of microtubules in the mitotic spindle

Answer 29

kinetochore microtubule, polar microtubule, & astral microtubule

Question 30

microtubule containing structures

Answer 30

cell body - contains singlets cilia/flagella - contain doublets for motion basal body/centriole - contain triplets

Question 31

MAPs

Answer 31

microtubule associated protein - stabilize microtubules

Question 32

What are the roles of motor proteins, microtubules, and microfilaments in the movement of cell contents?

Answer 32

Organelles will have motor proteins (kinesin/dynein/myosin) on them based on where they want to move materials & what structure the material will move along (microtubules/microfilaments). They will likely have more than one type.

Question 33

phases of mitosis

Answer 33

interphase, prophase, prometaphase, metaphase, anaphase, & telophase/cytokinesis

Question 34

interphase

Answer 34

microtubules radiate away from MTOC (microtubule organizing center)

Question 35

prophase

Answer 35

centrism has replicated and moved

Question 36

prometaphase

Answer 36

microtubules capture chromosomes - motor proteins move chromatids to end of the microtubules until attached on both sides and stabilized by the tension (bioriented)

Question 37

metaphase

Answer 37

microtubules line up the chromosomes through a combination of treadmilling and motor proteins

Question 38

anaphase

Answer 38

microtubules pull chromosomes to opposite poles through microtubules shrinkage & sliding

Question 39

telophase/cytokinesis

Answer 39

each cell has 1 centrisome and 1 set of chromosomes

Question 40

kinesin 3

Answer 40

located at kinetochore; enhances microtubule disassembly during mitosis