Lecture 14

Question 1

In chromosome packing, what does the interphases chromosomes look like?

Answer 1

• “beads on a string”
• chromatin fiber packed nucleosomes

Question 2

In chromosome packing, what do mitotic chromosomes look like?

Answer 2

• chromatin fiber folded into loops
• entire mitotic chromosome

Question 3

What is the net result of chromosome packing

Answer 3

Each DNA molecule has been packaged into a mitotic chromosome that is 10,000 Fold shorter than its fully extended length

Question 4

What occurs during the nuclear envelope breakdown during mitosis?

Answer 4

• Nuclear lamins form dimers and polyerize to form intermediate filaments
• serine residues of lamins are phosphorylated by M-Cdk
• Phosphorylated lamins depolymerize which leads to disintegration of lamin meshwork
• Nuclear envelope fragments into vesicles

Question 5

What ties together the sister chromatids in M phase?

Answer 5

Cohesion

Question 6

What needs to happen to form the mitotic spindle?

Answer 6

The centrosome has to be duplicated

Question 7

What is the microtubule system that forms between the two centrosomes?

Answer 7

spindle

Question 8

What do the ends of the microtubules attach to?

Answer 8

the kinetochores of the sister chromatids

Question 9

What do the spindle function in?

Answer 9

High fidelity segregation of chromosomes

Question 10

What happens after metaphase?

Answer 10

The ubiquitin ligace APC is activated which leads to the ubiquination and degradation of securing

Question 11

What is the results of activated ligace APC?

Answer 11

the active separate cleaves cohesion which initiates anaphase

Question 12

What pulls chromosomes to the centrosomes?

Answer 12

Microtubule shortening

Question 13

Where do microtubules disassemble?

Answer 13

At kinetochores

Question 14

What helps move the microtubules towards their spindle pole?

Answer 14

Shortening of kinetochore microtubules, forces are generated at kinetochores

Question 15

What initiates cytokinesis?

Answer 15

contractile ring made of acting filaments and myosin motors

Question 16

What is responsible for membrane abscission

Answer 16

ESCRT lll / Vps4: contractile ring

Question 17

Why is the regulation of CDKs important

Answer 17

to pause the cell cycle until the cell cycle problem is solved

Question 18

What occurs at the spindle assembly checkpoint?

Answer 18

• Mad2 associates with kinetochore until microtubule attachs
• Mad 2 binds to Cdc20 and prevent APC activation
• When microtubule attach to kinetochore Mad2 is released and Cdc20 can bind to APC to ubiquitinate securin (anaphase), which leads to the cleaving of the cohesion rings and the separation of the sister chromatids

Question 19

What initiates DNA damage checkpoint?

Answer 19

p53

Question 20

Cdk inhibitor p21 blcoks what

Answer 20

cell cycle until DNA damage is repaired

Question 21

What happens if DNA damage cannot be repaired

Answer 21

p53 will come in and induce apoptosis