L19- Mechanisms of cell division 1

Question 1

What happens in each of these stages?

1. Prophase
2. Pro-metaphase
3. Metaphase
4. Anaphase
5. Telophase
6. Cytokinesis

Answer 1

1. chromosomes condense
2. attach to spindle
3. chromosomes align in middle
4. chromosomes separate away
5. seperate DNA
6. Divide cytoplasms and cells

Question 2

From S phase onwards what are the sister chromatids held together by?

Answer 2

Cohesin rings

Question 3

What does the centrosome duplicate and what does this?

Answer 3

The s phase by the S-cdk that controls DNA replication.

Question 4

What does the centrosome do in the cell cycle?

Answer 4

Duplicates, seperates and nucleates MTs wihch form the mitotic spindle.

Question 5

What activates condensins in prophase?

Answer 5

Phosphorylation by M-Cdk

then DNA stays condensed until after cytokinesis

Question 6

What happens in prophase?

Answer 6

Chromosomes condense. Centrosomes separate and nucleate more MTs. The mitotic spindle starts to form.

Question 7

What does the spindle contain?

Answer 7

3 different groups of microtubules

Question 8

What happens to the number of microtubules, nucleated by the centrosomes from prophase?

Answer 8

The number increases. Microtubules are more dynamic. Change from grow to shrink more often.

Question 9

What is a catastrophe?

Answer 9

The MTs switch from growing to shrinking

Question 10

Why do more catastrophes happen after prophase?

Answer 10

Some MAPs (which stabilise MTs) are inactivated when phosphorylated by the mitotic kinase M-Cdk.
Proteins that trigger MT catastrophes are activated in mitosis.

Question 11

Does phosphorylation activate or inactivate the following and what is the consequence?

a. Cdc25
b. condensin
c. nuclear lamins
d. MAPs

Answer 11

a. Activates cdc25 - activates more cdKs
b. activates condensin- chromosomes condense (prophase)
c. Inactivates and activates nuclear lamina?- disassembles
d. Inactivates MAPs- MTs become more dynamic

Question 12

What establishes anti-parallel interactions between microtubules?

Answer 12

Kinesins

Question 13

What do anti-parallel interactions between microtubules do?

Answer 13

Stabilise the MTs

Question 14

Which kinesin can push poles apart by using the anti-parallel interactions between MTs?

Answer 14

Eg5 (a tetramer)

Question 15

What does Eg5 do?

Answer 15

1. Links anti-parallel MTs
2. Stabilises the MTs
3. pushes spindle poles apart

Question 16

What inhibits Eg5?

Answer 16

A drug- Monastrol

Question 17

IN which phase does the nuclear envelope disassemble?

Answer 17

Pro-metaphase

Question 18

What drives nuclear envelope disassembly?

Answer 18

MCdk. Phosphorylates the nuclear lamins. Has to dephosphorylate for reassembly to occur.

Question 19

What happens in the prophase to pro-metaphase transition?

Answer 19

Nuclear envelope disassembles, allowing MTs to interact with chromosomes.
Golgi disassembles
Secretion and endocytosis stop

Question 20

What is the kinetochore?

Answer 20

Specialised protein structure that assembles on to the centrome region of the chromosome in prophase. Where microtubules become embedded.

Question 21

What happens when kinetochores interact with growing and shrinking microtubules?

Answer 21

They capture the MTs and start moving using kinesins to move one kinetochore to the MT+ end and dynein to move the other towards the MT- end.

Question 22

Which direction can kinetochores move in pro-metaphase?

Answer 22

In both directions along MTs using dynein and kinesins

Question 23

WHat must the kinetochores have before mitosis can proceed?

Answer 23

Properly attached from both poles and be under tension. TENSION V IMPORTANT

Question 24

Are MTs allowed to grow and shrink when bound to kinetochores.

Answer 24

Yes.