Mitosis

Question 1

What are the 2 phases of anaphase?

Answer 1

1. Chromosomes condensation
2. Sister-chromatid resolution

Question 2

What is a chromosome?

Answer 2

linear DNA molecule

Question 3

What is a centromere?

Answer 3

region where the spindle attaches

Question 4

What are homologous structures?

Answer 4

have the same genes arranged in the same order (1 inherited from father, 1 from mother)

Question 5

What are chromatids?

Answer 5

newly copied DNA strands still joined to each other by a centromere

Question 6

How do cyclins lead to protein activation?

Answer 6

cyclins bind to CDKs (cyclin-dependent kinase), which leads to activation of the protein by phosphorylation

Question 7

How do you stop activation of a protein which drives the transition between different stages of the cell cycle?

Answer 7

Destruction of the cyclin will stop activation of the protein.

Question 8

What controls the transition between metaphase & anaphase?

Answer 8

controlled by APC (anaphase-promoting complex)

Question 9

What complex is involved in driving entry into mitosis

Answer 9

M-Cdk trigger

Question 10

What occurs following the activation of the M-Cdk trigger?

Answer 10

• assembly of the mitotic spindle
• each sister chromatid is attached to an opposite pole
• chromosome condensation
• breakdown of the nuclear envelope
• rearrangement of the actin cytoskeleton + Golgi

Question 11

Describe the process by which M-cyclin/Cdk triggers entry into mitosis

Answer 11

1. M-cyclin/Cdk1 complex formed
2. Cdk-activating kinase (CAK) can then phosphorylate the complex at an activating location.
3. Cdc25 then gets phosphorylated, which will then attach to Cdk, removing the phosphate from the M-Cdk complex, activating it.
4. On another hand, the phosphorylation of an inhibitory location can take place as a result of the action of Cdk-inhibitory kinase (Wee1). This inhibits its action.

Question 12

What activates Cdc25?

Answer 12

S-Cdk complexes. Once started positive feedback will inhibit Wee1 & activate more Cdc25

Question 13

How does APC (anaphase-promoting complex) drive transition form metaphase to anaphase?

Answer 13

Driven by protein destruction - cyclin is targeted, which leads to the cyclin changing in its protein expression (NOT THE Cdk).

Question 14

How is cyclin destroyed during the APC (anaphase-promoting complex)?

Answer 14

Ubiquitin attaches to the cyclin, leading to destruction (a tag for destruction)

Question 15

What are 2 targets for APC?

Answer 15

• S&M cyclins (if destroyed, most CDKs are inactivated)
• Securin (protects the protein linkages that hold sister chromatids together, therefore, its destruction activates a protease that separates the sister chromatids)

Question 16

What is the 2-hit hypothesis?

Answer 16

Most genes need mutations on BOTH alleles to cause a phenotypic change?

Question 17

What is a loss of a single tumour-suppressor gene?

Answer 17

Loss of heterozygosity

Question 17

What do we get a loss-of-heterozygosity?

Answer 17

• either a second hit
• loss of one of the chromosomes that still have a wild type allele

Question 18

What is the phrase given when chromosomes don’t separate properly?

Answer 18

Chromosome non-disjunction

Question 19

What constitutes a successful mitosis?

Answer 19

sister chromatids going to opposite poles

Question 20

What technique is used to attach the 1 kinetocore to spindle pole?

Answer 20

Trial & error

Question 21

How is appropriate spindle fibre attachment sensed?

Answer 21

tension

Question 22

Describe what correct spindle attachment would consist of?

Answer 22

• kinetocores pulled in opposite directions (BUT sister chromatids resists –> tension)

Question 23

Describe what incorrect spindle attachment would consist of?

Answer 23

Tension is lower (loosens the microtubule attachment size)

Question 24

What occurs during Anaphase A?

Answer 24

Separase breaks the cohesin bridges between chromosomes, and the kinetochore microtubules shorten, dragging the chromosomes towards the two poles of the cell.

Question 25

What occurs during Anaphase B?

Answer 25

Astral microtubules slide across each other, further pulling the cells apart.

Question 26

What process should normally occur when there is a loss of heterozygosity by non-disjunction?

Answer 26

Elimination by apoptosis

Question 27

What do loss of heterozygosity by mitotic recombination & gene conversion have in common?

Answer 27

They both lead to 2nd hit - 2nd copy inactivation