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Cell & Molecular Biology > Mitosis > Flashcards

Mitosis Flashcards

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1
Q

What are the 2 phases of anaphase?

A
  1. Chromosomes condensation
  2. Sister-chromatid resolution
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2
Q

What is a chromosome?

A

linear DNA molecule

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3
Q

What is a centromere?

A

region where the spindle attaches

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4
Q

What are homologous structures?

A

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

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5
Q

What are chromatids?

A

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

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6
Q

How do cyclins lead to protein activation?

A

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

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7
Q

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

A

Destruction of the cyclin will stop activation of the protein.

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8
Q

What controls the transition between metaphase & anaphase?

A

controlled by APC (anaphase-promoting complex)

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9
Q

What complex is involved in driving entry into mitosis

A

M-Cdk trigger

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10
Q

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

A
  • 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
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11
Q

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

A
  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.
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12
Q

What activates Cdc25?

A

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

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13
Q

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

A

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

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14
Q

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

A

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

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15
Q

What are 2 targets for APC?

A
  • 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)
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16
Q

What is the 2-hit hypothesis?

A

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

17
Q

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

A

Loss of heterozygosity

17
Q

What do we get a loss-of-heterozygosity?

A
  • either a second hit
  • loss of one of the chromosomes that still have a wild type allele
18
Q

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

A

Chromosome non-disjunction

19
Q

What constitutes a successful mitosis?

A

sister chromatids going to opposite poles

20
Q

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

A

Trial & error

21
Q

How is appropriate spindle fibre attachment sensed?

A

tension

22
Q

Describe what correct spindle attachment would consist of?

A
  • kinetocores pulled in opposite directions (BUT sister chromatids resists –> tension)
23
Q

Describe what incorrect spindle attachment would consist of?

A

Tension is lower (loosens the microtubule attachment size)

24
Q

What occurs during Anaphase A?

A

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

25
Q

What occurs during Anaphase B?

A

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

26
Q

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

A

Elimination by apoptosis

27
Q

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

A

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

28
Q
A

Cell & Molecular Biology (20 decks)

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