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Cell and Molecular > L7 - Mitosis and Meiosis > Flashcards

L7 - Mitosis and Meiosis Flashcards

1
Q

Cell proliferation

A

Rates of division must be regulated to maintain cell numbers
During DNA replication each chromosome pair is duplicated to give rise to sister chromatids

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2
Q

What are the cell cycle phases?

A

G1
S - DNA replication
G2
M - mitosis and cytokinesis

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3
Q

Mitosis phases

A

Prophase - condensation of sister chromatids
Metaphase - attachment of mitotic spindle to kinetochore by microtubules
Anaphase - separation of sister chromatids

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4
Q

Why are Yeast a good genetic model for the cell cycle?

A 
Fission or budding 
Advantages 
- Rapid division rate < 1 hour 
- Cell cycle control genes highly conserved 
- Can be grown as haploids or diploids
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5
Q

Why is studying genes crucial for cell survival?

A

Diploids used to maintain lethal mutations that are then studied as haploids.

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6
Q

Temperature sensitive mutations

A

Allow growth at permissive temperatures

Cell division cycle genes - cdc genes

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7
Q

Why are Xenopus a good biochemical model for the cell cycle?

A

Easy to collect eggs
Rapid division rate
Large size makes purification for proteins easier
Manipulated by injection of RNAs or chemicals into oocyte

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8
Q

Cell free mitosis in the Xenopus

A

Deplete cytoplasm of different proteins using antibodies

Remove cytoplasm at different stages to study changes over time

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9
Q

G1/S checkpoint

A

Is environment favourable

Is DNA damaged

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10
Q

G2/M checkpoint

A

Is environment favourable
Is DNA damaged
Is all DNA replicated

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11
Q

Metaphase/anaphase checkpoint

A

Are all chromosomes attached to spindle

Where you find the anaphase promoting complex

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12
Q

What are cyclically activated proteins?

A

Cyclins

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13
Q

Cyclins role

A

Expressed at different levels during the cell cycle
Bind to CDKs to activate them
Phosphorylate proteins that are specific to certain stages of cell cycle

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14
Q

How do proteins modify CDK activity?

A

Through phosphorylation and binding

  • Cyclins
  • Wee1 kinase and Cdc25 phosphatase
  • P27
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15
Q

Wee1 role

A

Adds an inhibitory phosphate

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16
Q

Cdc25

A

Removes the inhibitory phosphate

17
Q

Anaphase promoting complex mechanism

A

It is a ubiquitin ligase

  1. Active M-cyclin CDK complex which needs to be removed to finish mitosis
  2. A polyubiquitin chain is added to M-cyclin - enzymes E1 and E2
  3. Leads to degradation of M-cyclin in the proteasome
18
Q

What else does anaphase promoting complex ubiquitinate?

A

S-cyclin and securing

19
Q

Meiosis

A

Diploid organisms have two versions of each chromosome - homologues
- Homologues are either paternal or maternal
Resembles mitosis except there are steps that segregates homologous chromosomes

20
Q

How does crossing over occur?

A

Pairing of homologues before segregation allows for crossing over

21
Q

Meiosis I - crossing over and segregation mechanism

A
  1. Takes place when homologues pair up
  2. Homologous are replicated and pair up on spindle
  3. Crossing over occurs
  4. Separation of homologous at anaphase
    - Haploid cells
22
Q

Why do sex chromosomes behave like homologues during sperm formation?

A

Due to small regions of homology

23
Q

Meiosis II

A

Resembles mitosis
Separation of sister chromatids at anaphase II
Cells are haploid instead of diploid

24
Q

Meiotic prophase I

A

Homologues pair up and held by centromeres

25
Q

What facilitates pairing in prophase I?

A

Synaptonemal complex

DNA base pairing between homologues

26
Q

Homologous recombination between non-sister chromatids?

A

Aligns chromosomes ready for anaphase and facilitates formation of synaptonemal complex
Allows for genetic recombination between paternal and maternal DNA on the same chromosome

27
Q

Why is genetic variation important?

A

Crucial for evolution

Also creates medical conditions

28
Q

How does genetic variation occur?

A

Mistakes during meiosis I result in gametes with an extra chromosome or lacking a homologue

  • Nondisjunction
  • Cells that arise from these gametes are called aneuploid
    • 4% of mammalian sperm
    • 20% of mammalian eggs

Cell and Molecular (24 decks)

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