Chapter 4: 4.3 Karyokinesis and Cytokinesis

Question 1

Define:

Cytokinesis

Answer 1

The division of membranes during mitosis to separate the two daughter cells

Question 2

Define:

Karyokinesis

Answer 2

The separation of chromosomes during mitosis that happens during anaphase but starts in interphase when microtubules form

Question 3

What does MTOCs mean?

Answer 3

Microtubule organizing centres

Question 4

How many MTOCs are there?

Answer 4

2

Question 5

What are the MTOCs called during different phases? What are their half-lives?

Answer 5

1. Centrosome during interphase (5 minute half-life)
2. Mitotic poles during mitosis (5 seconds half-life

Question 6

Describe:

Centrosomes

Answer 6

Made up of 2 centrioles per pole

Question 7

What does centrosome make?

Answer 7

Kinetochore microtubules which bind to the chromatids

Question 8

What does mitotic poles make?

Answer 8

Polar microtubules

Question 9

What do polar microtubules do?

Answer 9

Extend from one pole to the other to stretch the cell

Question 10

Define:

Kinesin-13

Answer 10

A motor protein
* Regulates the depolymerization of the microtubule by bending it and making it less stable

Question 11

What else might Kinesin bind to? Describe the process

Answer 11

May bind to the chromatids
* Causes the plus end to shrink to bring the chromatids to the poles where the MTOCs are

(Mechanism not well known)

Question 12

Define:

XMAP215

Answer 12

Stabilizes the microtubule by inhibiting Kinesin-13

Question 13

Together, Kinesin-13 and XMAP215…

Answer 13

Regulate the dynamic instability of the microtubule

Question 14

True or False:

Kinesin-13 is inhibited by phosphorylation

Answer 14

False, Kinesin-13 is constantly active throughout

Question 15

What is XMAP215 inhibited by?

Answer 15

Inhibited by phosphorylation
* Controls the dynamic instability

Question 16

When is XMAP215 inhibited?

Answer 16

During mitosis

Question 17

In Anaphase A:

What occurs?

(4 points)

Answer 17

• Chromosome separation
• Binding of microtubule to kinetochore
• Kinesin-13 mediates depolymerization so chromosome moves to negative end
• Motor proteins pull the chromosome along the shortening end to separate the chromatids

Question 18

In Anaphase B:

What occurs?

Answer 18

• Cell elongation, pushes poles apart
• Uses polar microtubules which push against each other
• Uses both kinesin and dynamin motor proteins

Question 19

What does the activation of RhoA trigger?

Answer 19

Triggers actin polymerization and myosin activity

Question 20

What does the contractile ring that results from activation of RhoA result in?

Answer 20

Pinching of membrane in the middle to separate the two daughter cells