4. cellular reproduction: mitosis and cytokinesis

Question 1

Cytoskeletal dynamics during mitosis

Answer 1

• 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

Question 2

mitotic spindle has 3 sets of micro tubules:

Answer 2

astral microtubules
kinetochore microtubules
polar microtubules

Question 3

astral microtubules

Answer 3

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

Question 4

kinetochore microtubules

Answer 4

attach to chromosomes at kinetochore; pull chromosomes to different poles

Question 5

Polar microtubules

Answer 5

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

Question 6

microtubules have…

Answer 6

a polarity

alpha and beta tubulin

Question 7

minus (-) ends of microtubules

Answer 7

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

Question 8

Plus (+) ends microtubules

Answer 8

all point away from centrosome
beta end
rapidly growing end

Question 9

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

Answer 9

high at the +end and low at the -end

Question 10

two key events in spindle assembly:

Answer 10

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

Question 11

which are the heads that are walked on

Answer 11

dyneins and kinesins

Question 12

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

Answer 12

S, two

Question 13

what happens during prophase?

Answer 13

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

Question 14

motor proteins

Answer 14

• kinesins

- dyneins

Question 15

kinesins

Answer 15

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

Question 16

dyneins

Answer 16

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

Question 17

late prophase

Answer 17

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

Question 18

attachment of microtubules to chromosomes

Answer 18

• 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

Question 19

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

Answer 19

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

Question 20

what generates chromosomal movement?

Answer 20

A combination of micro-tubular dynamics and motors:

• rapid polymerization and depolymerization occurs at the + end of microtubules
• microtubule motors assist in two things

Question 21

microtubules motors assist in:

Answer 21

1. maintaining flow of tubulin subunits

2. tethering the kinetochore

Question 22

treadmilling

Answer 22

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

Question 23

depolymerization

Answer 23

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

Question 24

polymerization

Answer 24

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

Question 25

MT motors

Answer 25

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

Question 26

Spindle checkpoint

Answer 26

-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

Question 27

5 mechanisms of the spindle checkpoint

Answer 27

- 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

Question 28

Cytokinesis is different for plants and animals cells

Answer 28

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

Question 29

Actin and Myosin ll form what?

Answer 29

the contractile ring

Question 30

what does head rotation of myosin cause?

Answer 30

sliding of actin

Question 31

what is the evidence for myosin ll in Cytokinesis?

Answer 31

Treatments: -myosin II knock-outs (gene for myosin II is deleted) -antisense inhibition of myosin II mRNA -anti-myosin II antibodies treatments results: cells that can replicate their chromosomes, but are unable to divide, resulting in large, multi-nucleated cells

Question 32

Why use antibodies as tool for inhibiting protein functions?

Answer 32

- an antibody will bind with high specificity to just one target molecule (called its antigens) (many sorts of both) - binding an antibody to a protein MAY disrupt the normal function of that protein (due to steric hindrance) - antibody binding to myosin prevent it from working properly, so the cells failed to divide

Question 33

What is a benefit of being multinucleated?

Answer 33

rapid gene expression-lots of RNA and protein

Question 34

mitosis without cell division in early insect embryos

Answer 34

during early fly development, nuclear division occur without cellular division the early embryo is called a syncytial blastoderm the nuclei can be studied by GFP-labeling of chromosomes (remember not all mutlinucelated cells arise in this manner)

Question 35

multinucleated striated muscle cells arise by_______

Answer 35

cell fusion

Question 36

Meiosis is a cell division without DNA replication

Answer 36

- 2 sequential cell divisions without an intervening phase of DNA replication - results in 4 haploid cells (n=1 - each cell has only one copy of every centrosome, not 2, as in a haploid organism) - in animal cells, meiosis produces the gametes (sperm and eggs)

Question 37

securin needs to be degraded in order for ________________

Answer 37

sister chromatids to detach

Question 38

mitosis steps (5)

Answer 38

[prophase]- nuclear envelope disappears; chromosomes condense [prometaphase]-mitotic spindle forms; chromosomes attach to spindle [metaphase]-chromosomes aligned along equator [anaphase]-chromatids separate; chromosomes migrate to poles [telophase]-chromosomes decondense; nuclear envelope forms