Mitosis

Question 1

name the stages of mitosis

Answer 1

prophase, prometaphase, metaphase, anaphase, telophase

Question 2

prophase

Answer 2

chromosomes condense and become visible

bipolar spindle develops

Question 3

prometaphse

Answer 3

nuclear envelope dissolves

chromosomes begin to migrate to equatorial plane (metphase plate) and are seen to contain two chromatids

kinetochore forms

Question 4

metaphase

Answer 4

chromosomes are fully condensed and located at metaphase plate

Question 5

anaphase

Answer 5

each centromere splits

the two chromatids of each chromosome are pulled to opposite poles

Question 6

telophase

Answer 6

chromosomes reach poles and start to decondense

nuclear membrane reforms due to dephosphorylation of the lamins and other nuclear envelope components

chromosome surface is necessary to reassemble the nuclear components

cytoplasm starts to divide

Question 7

G2-M transition

Answer 7

regulated by Cyclin B1/Cdk1

after complex formation, rapidly phosphorylated by Cdk-activating kinase (CAK, activating) and Wee1 (deactivating)

Cdc25 fully activates the complex by removing the inhibitory phosphorylation

blocking of export form the nucleus allows for a rapid build-up and trickers mitosis

Cyclin A/Cdk2 also phosphorylates subunits of the condensing complex and helps with chromosome condensation and microtubule assembly

Question 8

mitotic cyclin positive feedback

Answer 8

active M-Cdk activates more active Cdc25 phosphatase

Question 9

Describe some of the regulatory pathways in the DNA damage checkpoint.

Answer 9

Cdc2 is the old name for Cdk1

phosphrylation of CHK2 and CHK1 by ATM/ATR leads to inactivation of the Cyclin B/Cdk1 complex until DNA damage is resulved

p53 is also activated along with BRCA1

14-3-3 is an adaptor protein that binds to Cdc25 and exports it into the cytoplasm

Question 10

disassembly of the nuclear envelope during prophase/prometaphase

Answer 10

phosphorylation of nuclear envelope, core complexes, lamins, etc. causes it to fall apart

nuclear envelope gets subsumed into the ER

transcription and translation are shut off through phophorylation as well

the Golgi becomes fragmented as well

Question 11

condensin

Answer 11

a complex of several proteins that form a circular structure and introduces superhelical twists into the DNA

DNA topoisomerase is present to disentangle entwined sister chromatids

Question 12

Aurora B kinase

Answer 12

phosphorylates Histone H3

histone H1 is also phosphorylated by Cdk1

Question 13

kinetochore

Answer 13

a complex protein structure that forms in the middle of the chromosome at the centromere

one on each sister chromatid, face opposite to each other

microtubules attach to this structure

Question 14

microtubule spindle formation

Answer 14

requires at least 7 kinesins and dynein

a combination of kinetochore microtubules, interpolar microtubules, and astral microtubules

asters radiate out of the centrosomes, associate with each other through kinesin motor proteins, also associates with the cortex of the cell

Question 15

kinetochore microtubules

Answer 15

plus ends embedded in the kinetochore and minus ends in the spindle pole

form bundles of 20 microtubules called kinetochore fibers

Question 16

interpolar microtubules

Answer 16

long microtubules extending across the length of the spindle, but not necessarily associated with the spindle poles

arranged in an antiparallel array

Question 17

astral microtubules

Answer 17

radiate from the spindle poles and help orient the spindle in relation to the cell cortex

Question 18

erroneous spindle attachments

Answer 18

amphitelic - normal attachment

monotelic - one attaches before the other, resolved very quickly

syntelic - single spindle attaches to both kinetochores

merotelic - a single sister chromatid attaches to both spindles

Question 19

microtubule treadmilling at the kinetochore

Answer 19

happens during metaphase

poleward state, dissociation of GDP-bound tubulin from shortening end, centromeres stretch

neutral state, association of GTP bound tubulin of growing end

kinetochore proteins such as chromokinesin can sense the tension and ensure that the chromosomes align equally at the metaphase plate

Question 20

spindle assembly checkpoint

Answer 20

even a single improperly attached kinetochore can send out strong signals to prevent anaphase from happening

APC (anaphase promoting complex) is activated once the checkpoint is passsed

APC ubiquitinylates the securin protein, releasing separase, which can then degrade the cohesion complex

Question 21

APC

Answer 21

E3 ubiquitin ligase, leads to the degradation of cyclins during anaphase, tirggers events in anaphase

leads to degradation of securin, freeing separase to degrade the cohesion complex

Question 22

Anaphase A

Answer 22

the kinetochore fibers shorten, moving the chromatids toward the poles

Question 23

Anaphase B

Answer 23

the spindle elongates and the poles separate due to motor driven interactions between interpolar microtubules and intrinsic mobility of the poles themselves

Question 24

cytokinesis

Answer 24

process that divides the mitotic cell into two daughter cells

contractile ring has an actin-myosin complex that is regulated by local release of calcium, which activates the myosin light chian kinase, activating myosin II in the ring

the cleavage furrow forms where the plasma membrane is constricted and the cell pinches in two

the cytoplasmic bridge forms a highly ordered array of microtubules and components from the central spindle called the midbody

eventually the cells separate and the midbody is lost, but in spermatogenesis, the cell’s don’t seaparate the the midbody becomes a ring canal