18.3 The Events of the M Phase

Question 1

M phase involves a () of all cell components

Answer 1

major reorganization

Question 2

4 primary stages of mitosis:

Answer 2

1. prophase
2. metaphase
3. anaphase
4. telophase

Question 3

beginning of prophase is markes by the appreance of () (each of which consists of 2 sister chromatids; daughter DNA molecules produced in S)

Answer 3

condensed chromosomes

Question 4

sister chromatids are attached to each other at the ()

Answer 4

centromere

Question 5

the centromere is a chromosomal region to which proteins bind to form the() → site of eventual attachment of mitotic spindle microtubules

Answer 5

kinetochore

Question 6

cytoplasmic changes leading to the development of mitotic spindle are initiated; duplicated centrosomes move towards opposite sides of the nucleus → serve as the two poles of the () (begins to form during late prophase)

Answer 6

mitotic spindle

Question 7

in yeasts, the nuclear envelope remains intact ()

Answer 7

closed mitosis

Question 8

in higher eukaryotes, prophase ends when the nuclear envelope breaks down ()

Answer 8

open mitosis

Question 9

transition period between prophase and metaphase

Answer 9

prometaphase

Question 10

what happens in prometaphase

Answer 10

spindle microtubules (from both poles) attach to the kinetochores of condensed chromosomes

Question 11

chromosomes shuffle back and forth until they eventually align on the metaphase plate in the center of the spindle → beginning of ()

Answer 11

metaphase

Question 12

transition from metaphase to anaphase is triggered by the ()

Answer 12

breakage of the link between sister chromatids

Question 13

mitosis phase where nuclei reform and chromosomes decondense

Answer 13

telophase

Question 14

() usually begins during late anaphase and is almost complete by the end of telophase

Answer 14

cytokinesis

Question 15

() is the master regulator of M phase transition

Answer 15

Cdk1/cycB protein kinase (MPF)

Question 16

mitotic protein kinases: (1) and (2) families are activated coordinately with Cdk1 to signal entry into M phase

Answer 16

1. Aurora kinase (Aurora A and B)
2. Polo-like kinase

Question 17

Cdk1, Aurora, and Polo-like kinases are activated in a positive feedback loop that works to initiate the ff. downstream pathways needed for M phase transition:

Answer 17

1. chromatin condensation
2. nuclear envelope breakdown
3. fragmentation of Golgi apparatus
4. spindle formation

Question 18

nuclear envelope breakdown involves changes in all of nuclear envelope components:

Answer 18

• fragmentation of nuclear membranes
• dissociation of nuclear pore complexes
• depolymerization of nuclear lamina

Question 19

depolymerization of nuclear lamina results from the (1) by (2)

Answer 19

1. phosphorylation of lamins
2. Cdk1/cycB

Question 20

Golgi breakdown is mediated by phosphorylation of proteins by ()

Answer 20

Cdk1 and Polo-like kinases

Question 21

centrosome maturation, separation, and spindle assembly during prophase are driven by phosphorylation of Aurora and Polo-like kinases at the ()

Answer 21

centrosomes

Question 22

during prophase, spindle formation results from the ()

Answer 22

dynamic instability of microtubules

Question 23

() allows spindle microtubules to attach to chromosomes at the kinetochores

Answer 23

breakdown of nuclear envelope

Question 24

proteins assembled at the kinetochore include () → involved in the interactions of chromosomes with microtubules

Answer 24

Aurora B kinase

Question 25

chromosomes in prometaphase shuffle back and forth due to activity of () at the kinetochore and centrosomes

Answer 25

microtubule motors

Question 26

balance of forces acting on the chromosomes leads to their alignment on the ()

Answer 26

metaphase plate

Question 27

the mitotic spindle consists of:

Answer 27

- kinetochore microtubules: attached to the chromosomes - interpolar microtubules: overlap in the center of the cell - astral microtubules: radiate outward from centrosome towards cell periphery

Question 28

chromosome condensation is driven by (1) and (2) (members of structural maintenance of chromatin or SMC proteins), which contribute to chromosome segregation during mitosis

Answer 28

1. condensins 2. cohesins

Question 29

() bind to DNA in S phase and maintain linkage between sister chromatids after replication

Answer 29

cohesins

Question 30

as the cell enters M phase, () are activated by phosphorylation of both Cdk1 and Aurora B kinase

Answer 30

condensins

Question 31

once condensins are activated by (1), they replace (2) along most of the length of the chromosome → sister chromatids remain linked only at the centromere

Answer 31

1. Cdk1 and Aurora B kinase 2. cohesins

Question 32

condensins then induce chromatin condensation by forming () → formation of metaphase chromosomes

Answer 32

DNA loops

Question 33

the () monitors the alignment of chromosomes on the metaphase spindle

Answer 33

spindle assembly checkpoint

Question 34

progression to anaphase is mediated by activation of () → results from phosphorylation by Cdk1/cycB

Answer 34

APC/C ubiquitin ligase

Question 35

presence of () is sufficient to prevent APC/C activation

Answer 35

even 1 unaligned chromosome

Question 36

unattached kinetochores lead to the assembly of the (), which inhibits APC/C

Answer 36

mitotic checkpoint complex (MCC)

Question 37

MCC is no longer formed once () → APC/C is activated

Answer 37

all chromosomes are aligned on the spindle

Question 38

MCC consists of 4 proteins:

Answer 38

- BubR1 - Bub3 - Mad2 - Cdc20

Question 39

() is required for activation of APC/C, but it remains inactivated when bound to Mad and Bub proteins in the MCC

Answer 39

Cdc20

Question 40

Cdc20 is required for activation of APC/C, but it remains inactivated when bound to () proteins in the MCC

Answer 40

Mad and Bub

Question 41

activation of APC/C results in the ubiquitylation and degradation of 2 key target proteins that trigger metaphase to anaphase transition:

Answer 41

1. degradation of cycB → Cdk1 inactivation → cell proceeds to exit mitosis 2. degradation of securin (component of cohesins)→ dissociation of sister chromatids, allowing them to move to opposite poles of the mitotic spindle

Question 42

degradation of securin activates () → degrades cohesin

Answer 42

separase

Question 43

cytokinesis usually starts shortly after (1) starts; triggered by the (2)

Answer 43

1. anaphase 2. inactivation of Cdk1

Question 44

() remain active in anaphase and play important roles in coordinating nuclear and cytoplasmic division of the cell

Answer 44

Aurora and Polo-like kinases

Question 45

cytokinesis of yeast and animal cells is mediated by a () (forms beneath the plasma membrane)

Answer 45

contractile ring of actin and myosin II filaments

Question 46

ring formation is activated by ()

Answer 46

Aurora and Polo-like kinases

Question 47

in plant cells, cytokinesis proceeds by the formation of ()

Answer 47

new cell walls and plasma membranes

Question 48

in early telophase, vesicles carrying cell wall precursors (from Golgi) accumulate at the ()

Answer 48

former site of the metaphase plate

Question 49

vesicles fuse to form a membrane-enclosed disk; polysaccharides from the matrix of the new cell wall called a ()

Answer 49

cell plate

Question 50

summarize how cytokinesis occurs in plant cells

Answer 50

1. in early telophase, vesicles carrying cell wall precursors (from Golgi) accumulate at the former site of the metaphase plate 2. vesicles fuse to form a membrane-enclosed disk; polysaccharides from the matrix of the new cell wall (called a cell plate) 3. cell plate expands outward (perpendicular to the spindle) until it reaches the PM 4. membrane surrounding cell plate then fuses with parental PM → divides the plant cell

Question 51

() between daughter plant cells are formed as a result of incomplete vesicle fusion

Answer 51

plasmodesmata