Lecture 13 - more cell division

Question 1

recap - 3 types of microtubules that form the mitotic spindle

Answer 1

kinetochore
interpolar
astral

Question 2

what is the metaphase checkpoint

Answer 2

• all kinetochores must each be attached to a spindle
  SPINDLE ASSEMBLY CHECKPOINT

Question 3

what is the metaphase checkpoint

Answer 3

• all kinetochores must each be attached to a spindle
  SPINDLE ASSEMBLY CHECKPOINT (SAC)

Question 4

what is Mad2

Answer 4

protein kinase
part of SAC complex at the kinetochore

Question 5

what does the SAC do

Answer 5

generates a stop signal at the kinetochore

Question 6

how does SAC get inhibited

Answer 6

the stop signal is only inhibited once kinetochore attaches to MT
then SAC proteins removed by dyenin

Question 7

what exactly is the stop signal produced by SAC

Answer 7

SAC makes APC inhibitor
APC is anaphase promoting complex
so naturally
SAC inhibits anaphase
since APC is blocked

Question 8

how does APC work

Answer 8

covalently binds to ubiquitin
this ubiquitin tags proteins to get degraded

M-cdk
and securin

Question 9

what would inhibiting Mad2 do

Answer 9

cytokinesis without anaphase
(even if there are no MT, still cytokinesis)
cuz cell cant tell that the kinetochores are unattached

Question 10

what are cohesins cleaved by in anaphase

Answer 10

protease called seperase

Question 11

when is separase activated

Answer 11

when SAC is fully inactivated

Question 12

how does securin get degraded

Answer 12

via ubiquination and protasome

Question 13

how does separase get activated

Answer 13

via active APC
and remember, APC can only be activated once SAC stops
and then once the separase is active it can go on to degrade cohesins

Question 14

what is anaphase A

Answer 14

sister chromatids get split, move towards the spindle poles
staying attached to kinetochore MTs which depolymerise = making them shorter in one direction pulling the chromatids to one end

Question 15

what is anaphase B

Answer 15

Spindle poles move further apart

Question 16

what creates the pushing force in anaphase B

Answer 16

kinesin Eg-5 which creates a sliding force between the MTs from the opposite poles
the interpolar MTs continue growing at plus ends

Question 17

what creates the pulling force in anaphase B

Answer 17

dyenin anchored in the cell cortex (thin network of actin filaments and actin-binding proteins that underlies the plasma membrane)
pulls the MT towards ends

Question 18

telophase specfic events

Answer 18

nuc envelope and nuc lamins reassemble
golgi reassembles
secretion and endocytosis restart

Question 19

what filaments form the contractile ring

Answer 19

actin and myosin ring
dynamic, so gets smaller around middle of the spindle

Question 20

what is different about plant cells

Answer 20

no centrosomes
no dyenin
spindle poles are broad = minus end directed kinesins

Question 21

what is used to make the plant cell membrane and cell wall

Answer 21

golgi derived vesicles