Chromosome segregation I

Question 1

M phase

Answer 1

• nucelar division (mitosis)
• cytoplasmic division (cytokinesis)
• takes about 1-2 hours within a total cell cycle

Question 2

Importance of chromosome segregation

Answer 2

• is essential for cell proliferation
• crucial to avoid aneuploidy

Question 3

Errors resulting from chromosome segregation

Answer 3

• cancer (somatic cells)
• down syndrome (gameto-genesis)

Question 4

Stages of mitosis

Answer 4

1. prophase
2. prometaphase
3. metaphase
4. anaphase
5. telophase
6. cytokinesis

Question 5

Prophase

Answer 5

• chromosomes start condensation
• centrosomes separate and form mitotic spindle

Question 6

Prometaphase

Answer 6

• nuclear envelope is broken down
• microtubules interact with chromosomes

Question 7

Metaphase

Answer 7

chromosomes bi-orient on spindle and align on metaphase plate

Question 8

Anaphase

Answer 8

sister chromatids separate and move towards the spindle poles, spindle poles move apart

Question 9

Telophase

Answer 9

chromosomes arrive at poles and decondense, nuclear envelope reassembles

Question 10

Cytokinesis

Answer 10

contractile ring makes cleavage furrow and divides the cytoplasm, creating two daughter cells

Question 11

Role of M-phase cyclin/CDK

Answer 11

promotes mitosis and various mitotic events (i.e. spindle assembly, kinetochore assembly, chromsome condensation)

Question 12

Regulation of CDKs

Answer 12

1. activation by phosphorylation and dephosphorylation of CDK
2. inactivation by proteolysis

Question 13

How do chromosomes prepare for mitosis

Answer 13

1. sister chromatid cohesion is established by cohesion complex during S phase
2. chromosomes are condensed in prophase

Question 14

Importance of sister chromatid cohesion

Answer 14

important for chromosome bi-orientation and ‘tells’ which chromatids are sisters to segregate in mitosis

Question 15

What are the three classes of spindle microtubules

Answer 15

1. Astral MTs radiate in all directions from the spindle poles and properly orient the spindle
2. Kinetochore MTs attach to kinetochores and regulate chromosome motion
3. Interpolar MTs inter-digitate at the spindle equator and generate forces for separation of the poles

Question 16

Microtubule structure

Answer 16

• made up of beta and alpha tubulins
• long hollow cylinders made of protofilaments
• assemble head-to-tail, creating profilaments

Question 17

GTP hydrolysis on tubulin beta

Answer 17

promotes microtubule depolymerisation, weakens bond in polymer

Question 18

Dynamic instability of microtubules is regulated by

Answer 18

1. Microtubule-associated proteins (MAPs)
2. Catastrophe factor (e.g. Kinesin-8, -13)

Question 19

Stabilisation of MT

Answer 19

frequency of catastrophes suppressed and/or growth rate enhanced, result in longer MTs

Question 20

Destabilisation of MT

Answer 20

frequency of catastrophes increased, result in shorter MTs

Question 21

Polymerisation and depolymerisation of kinetochore MTs

Answer 21

• regulate chromosome motion during metaphase and anaphase
• metaphase: microtubule flux
• anaphase: microtubule flux and depolymerisation at the + end

Question 22

MT associated motors

Answer 22

• kinesins and dyneins
• transport cargos along MTs and regulate sliding between MTs
• Dynein shows at the (-) end-directed motion
• Kinesins hsow at the (+) end-directed motion
• both motors have ATPase activity