4. cellular reproduction: mitosis and cytokinesis Flashcards Preview

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Flashcards in 4. cellular reproduction: mitosis and cytokinesis Deck (38)
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1

Cytoskeletal dynamics during mitosis

-essentially the process of partitioning newly replicated chromosomes into separate parts of the cell
-mitosis occurs as the last step of the cell cycle
-lasts approx 1 hours
-during that time the cell must build, them disassemble mitotic spindle

2

mitotic spindle has 3 sets of micro tubules:

astral microtubules
kinetochore microtubules
polar microtubules

3

astral microtubules

radiate from centrosome, form aster (centrosome is essentially a MTOC [microtubule organizing centre])
-help position mitotic apparatus, determine cleavage plane

4

kinetochore microtubules

attach to chromosomes at kinetochore; pull chromosomes to different poles

5

Polar microtubules

interdigitate (interlocking) with opposing pair; support framework; help push centrosomes apart

6

microtubules have...

a polarity
alpha and beta tubulin

7

minus (-) ends of microtubules

alpha
all point toward the centrosome
point away from kinetochore (=point of attachment to centrosome)

8

Plus (+) ends microtubules

all point away from centrosome
beta end
rapidly growing end

9

plus and minus ends of microtubules differs in their rates of assembly

high at the +end and low at the -end

10

two key events in spindle assembly:

1)Formation of poles
-spindle microtubules must "attach" or anchor to poles
2)capture of chromosome some
-spindle microtubules must attach to chromosomes

11

which are the heads that are walked on

dyneins and kinesins

12

in animal cells, duplication of centrosomes (MTOCs) occurs during _______ phase; each centrosome has ________ centrioles arranged perpendicularly to each other .

S, two

13

what happens during prophase?

centrosomes begin to move apart and migrate to poles for orientation of mitotic apparatus
-motor proteins are involved

14

motor proteins

-kinesins
-dyneins

15

kinesins

most walk toward +end of MT
-orange
push/ enlarge

16

dyneins

-end directed motor proteins
-round, blue
pull, shorten

17

late prophase

1. motor proteins help align microtubules
2. centrosome alignment
-bottom end of dyneins is anchored
-moving end of protein dynein is round top
-dynein -end directed MT motor protein
3. centrosome separation
-kinesin +end- directed MT motor protein
-lengthening of polar tubules can push centrosomes apart
-shortening of astral MT's can help pull centrosomes apart
- -end dynein

18

attachment of microtubules to chromosomes

-occurs at kinetochore
-+ends of MTs attach to outer layer
-centromeric chromatin has binding factors mediating MT attachment
-motor proteins help hold the MT and corona fibers together

19

Chromosome capture: rapid fluctuations in spindle MTs length occurs ___________.

-Occurs during pro-metaphase once nuclear envelope is broken down
-Dynamic MT acts a poker

20

what generates chromosomal movement?

A combination of micro-tubular dynamics and motors:
-rapid polymerization and depolymerization occurs at the + end of microtubules
-microtubule motors assist in two things

21

microtubules motors assist in:

1. maintaining flow of tubulin subunits
2. tethering the kinetochore

22

treadmilling

in this scenario, there is no net elongation/shrinking of the MT
page slide 14
red subunits added to +end and being pushed up to -end. -end looses subunits and quickly and subunits are added

23

depolymerization

In this scenario, there is a net loss at the + end, and the chromosome moves to the right
smaller

24

polymerization

in this scenario, there is a net gain at the +end and the chromosome moves away (to the left)
larger

25

MT motors

there is enough room fro tubulin subunits to be added or removed from kinetochore; the motor proteins hold the MT just far enough away from the kinetochore
-Dynenin and - directed MT motor walks on its head from the kinetochore to the centromere

26

Spindle checkpoint

-cell monitors the status of events in metaphase before going on to anaphase
(it is important that the chromosomes are all evenly lined up as the cell goes on to anaphase, so that the separation process goes smoothly)
-if one of the chromosomes is not at the metaphase plate it waits, to give it a chance to get there

27

5 mechanisms of the spindle checkpoint

-sister chromatids are held together by protein called securin
-the anaphase promoting complex (APC) causes ubiquitination of securin, thereby allowing chromatids to split apart
-Cdc20 is an activator of the Anaphase promoting complex (APC)
-MAD2 protein is bound to the kinetochore of un-aligned or improperly attached metaphase chromosomes
-Mad2 inhibits cdc20

28

Cytokinesis is different for plants and animals cells

animal cells: cleavage furrow
Plant cells: formation of cell plate

29

Actin and Myosin ll form what?

the contractile ring

30

what does head rotation of myosin cause?

sliding of actin