Lecture 9

Question 1

Mitosis describs the process of ________ and cytokinesis describes the process of __________

Answer 1

Replicating and segregating the sets of chromosomes, cytokinesis is making the 1 cell into 2

Question 2

Eukaryotic cell cycle 4 phases

Answer 2

-Growth phase (G1)
-Synthesis phase (S)
-Growth phase (G2)
-Mitotic (M)

Question 3

In cytokinesis, where are actin and myosin highly concentrated

Answer 3

Contractile ring

Question 4

What does the contractile ring do

Answer 4

Helps 2 cells pinch apart

Question 5

Cytokinesis is the final step in cell division in which the _________ of a single eukaryotic cell is divided to form two daughter cells

Answer 5

Cytoplasm

Question 6

First visible change in cytokinesis is the appearance of a

Answer 6

Cleavage furrow

Question 7

What structure is responsibe for the contractile ring

Answer 7

Cleavage furrow

Question 8

Contractile ring assembles beneath

Answer 8

Plasma membrane

Question 9

Contractile ring pulls membrane _______

Answer 9

Inward

Question 10

True or false: membrane vesicles fuse to PMAssembly of contractile ring

Answer 10

1. Actin, tubulin and myosin disassemble in mother cell
2. Monomeric actin and myosin accumulate at site of contractile ring (ANAPHASE)
3. Local actin polymerizes- mediated in part by formin- establishing site of nucleation by unbranched actin

Question 11

What happens as cleavage furrow deepens

Answer 11

Vesicles fuse to PM, surface area expansion

Question 12

Adding taxol during cytokinesis

Answer 12

Prevents depolymerization of MTs, cant break apart asters, cell dies

Question 12

Microtubules must _______ to facilitate formation of contractile ring

Answer 12

Depolymerize

Question 12

The midbody contains

Answer 12

The central spindle, consisting of densly packed microtubules of the spindle midzone (actin-tubulin)

Question 13

Disassembly of contractile ring

Answer 13

1. During contraction, actin filaments depolymerize and exit ring to maintain size and volume
   2.Contractile ring is completely disassembled with formation of Midbody
2. Midbody tethers daughter cells together (right before they seperate)

Question 14

Local activation of RhoA triggers

Answer 14

Assembly and contraction of contractile ring

Question 15

Some things RhoA does:

Answer 15

-regulates remodelling of actin skeleton
-promotes actin polymerization
-binds and activates formin to promote actin nucleation at contractile ring
-Activates Rho Kinases (such as ROCK1)

Question 16

Rho in muscle contraction

Answer 16

Rho –> mDia (formin) –> profilin –> actin polymerization

Question 17

What ensures equal distribution of chromosomes

Answer 17

Spindles signal for furrow formation midway between 2 poles (anaphase)

Question 18

ER during cytokinesis

Answer 18

Segregates during interphase, also necessary for orientation of contractile ring

Question 19

Mitochondria during cytokinesis

Answer 19

Multiply prior to segregation, localize to cleavage furrow - likely to supply energy

Question 20

Golgi during cytokinesis

Answer 20

Fragments during M-phase in mammals, form cell plate in plants

Question 21

Asymmetrical division

Question 22

Positioning of cleavage furrow 3 mechanisms

Answer 22

1. Astral stimulation model
2. Central spindle model
3. Astral relaxation model

Question 23

Astral stimulation

Answer 23

Signals being moved down the MTs toward the middle of the PM where furrow forms

Question 24

Central spindle stim model

Answer 24

Spindle mid zone (overlap) sends signals that transmit to cell cortex to activate Rho signalling pathway - formation of contractile ring

Question 25

Astral relaxation model

Answer 25

Relaxation of any contractile force where MTs meet PM - contractile force exerted only at cleavage furrow site