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BMS 242 - Advanced Cell and Molecular > Mitosis and Meisosis > Flashcards

Mitosis and Meisosis Flashcards

1
Q

Why must rates of cell division and the timings of the cell cycle be carefully regulated?

A

To maintain cell numbers in a given tissue and maintain tissue size

Prevent formation of tumours

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2
Q

What is the division rate of a proliferating mammalian cell?

A

One division per 24 hours

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3
Q

Do all cells divide?

A

No

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4
Q

What are the 4 stages of the cell cycle?

A

1) M phase - Nuclear division, followed by cytokinesis
2) G1 phase
3) S phase - DNA replication
4) G2 phase

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5
Q

What can happen in G1?

A

Cells can arrest in G1

Some cells can remain permanently in G1

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6
Q

What are the 5 phases of mitosis?

Describe them

A

1) Prophase
Condensation of sister chromatids

2) Prometaphase

3) Metaphase
Attachment of chromosomes to the mitotic spindle

4) Anaphase
Separation of sister chromatids

5) Telophase

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7
Q

Where does the mitotic spindle initiate from?

A

Centrioles

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8
Q

What happens to chromosomes during DNA replication?

A

The DNA in each chromosome (maternal and paternal) is duplicated to form SISTER CHROMATIDS

Sister chromatids are the segregates into daughter cells, so that each daughter cell receives one copy of each the maternal and paternal chromosome

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9
Q

What is the FISSION YEAST model for the cell cycle?

A

SP yeast:

  • When it divides, the cells stay together and created filaments
  • Spends a long time in G2 instead of G1
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10
Q

What is the BUDDING YEAST model for the cell cycle?

A

SC yeast:

  • Give rise to 2 daughter cells, where one is smaller than the other
  • Don’t have a G2 phase
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11
Q

Why is yeast an important model in the cell cycle?

A

Identified major genes involved in the cell cycle

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12
Q

What is the advantage of using yeast as a model for the cell cycle?

A

1) Rapid division rate (<1 hr)
2) Cell cycle control is HIGHLY conserved (human genes have exactly the same function)
3) Yeast can be grown as haploid or diploid

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13
Q

Why is it hard to study the genes in the cell cycle?

A
  • They are crucial for survival
  • If mutate the genes to see what they do, won’t be able to grow and maintain the cells
  • Cells will die
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14
Q

What techniques make it possible to study the cell cycle genes?

A

1) Cells with lethal mutations can be maintained as diploids (KO one copy of the genes)
- When want to study - turn into haploids

2) Temperature sensitive mutations allow growth at permissive temperatures
- Mutations function at lower temperatures
- At high temperatures - protein is inactivated

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15
Q

What genes control the cell cycle?

A

Cdc genes (cell-division-cycle)

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16
Q

Why is the xenopus a good biochemical model of the cell cycle?

A
  • Easy to collect eggs
  • Rapid division rate (30 mins)
  • Large size - easier to purify proteins
  • Cells produce A LOT of proteins
  • Can be manipulated by injection of RNAs or chemicals into the oocyte
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17
Q

Describe the process of ‘cell-free mitosis’

A

1) Purify cytoplasm from an xenopus oocyte
2) Add ATP and frog sperm
3) Mitosis occurs in the tube (but NO cell division or cytokinesis)
4) Makes more DNA and chromosomes

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18
Q

What did researchers do with the large amount of DNA and chromosomes produces by ‘cell-free mitosis’?

What did this identify?

A

1) Add antibodies for individual proteins - KO the protein in the sample and see where the cell cycle arrests
2) Remove cytoplasm at different time points and study the changes to the proteins over time

Identified regulatory and checkpoint genes

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19
Q

What are the 3 checkpoints in the cell cycle?

What are the questions asked at each checkpoint?

A

1) Start
Is the environment favourable?

2) G2/M
Is all the DNA replicated
Is the environment favourable?

3) Metaphase-to-anaphase
Are all the chromosomes attached to the spindle?

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20
Q

Why is the start checkpoint important?

A

A lot of energy is required for the steps after the start checkpoint - don’t want to waste energy

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21
Q

What are cyclins?

A
  • Proteins which are precisely regulated and expressed in different levels during the cell cycle
  • Bind to specific CDKs (cyclin-dependant kinases) to activate and regulate their activity
22
Q

What do CDKs do?

A

Phosphorylate many proteins which are specific to certain stages in the cell cycle

23
Q

How does Wee1 kinase modify CDK activity?

A

Phosphorylates CDK at a second point - inactivating the kinase activity by changing the shape of the CDK

24
Q

Where does Wee1 kinase phosphorylate CDKs?

A

NOT near the kinase domain

25
Q

How does Cdc25 modify CDK activity?

A

Removes the inhibitory phosphate added by Wee1 kinase (leaving only one phosphorylation by the kinase domain)

Activates the CDK

26
Q

How does P27 modify CDK activity?

A

Binds to the whole cyclin-CDK complex, inactivating it

27
Q

What is APC and what does it do?

A

Anaphase-promoting complex

A ubiquitin ligase which regulates entry into anaphase

By adding a poly-ubiquitin to M-cyclin in the M-cyclin/Cdk complex - to label the M-cyclin for degradation

28
Q

What 3 things does APC ubiquinate?

A

M-cyclin
S-cyclin
Securin

29
Q

What is Securin?

A

A molecule which holds sister chromatids together and allows anaphase to commence

30
Q

What determines if the cell cycle occurs?

A
  • Favourable extracellular environment
  • DNA damage
  • Un-replicated DNA
  • Chromosomes unattached to the spindle
31
Q

What is MITOSIS?

A

Formation of 2 daughter cells, containing the same number and kind of chromosomes as the mother cell

32
Q

What is MEOSIS?

A

Formation of 4 daughter cells, each with half the number of chromosomes as the mother - in order to generate genetically different gametes

33
Q

Which genes aren’t passed onto offspring?

A

Genes in somatic cells

34
Q

Which gene are passed onto offspring?

A

Genes within germ-line cells, which are set aside in the organism

35
Q

Are gametes diploid or haploid?

A

Haploid - only one homologue from each chromosome

36
Q

What is the difference between the steps of mitosis and meosis?

A

Meosis resembles mitosis, but there are EXTRA steps to segregate the homologous chromosomes

37
Q

What are homologous chromosomes?

A

Chromosomes which are similar in length, gene position and centromere location (maternal and paternal chromosomes)

38
Q

What happens before segregation of the homologues occurs?

A
  • Pairing of the duplicated homologues (maternal and paternal)
  • Crossing-over and recombination between the maternal and paternal chromosomes
39
Q

What is meiosis I?

A

Crossing over and segregation:
1) Germ cell with a single paternal and maternal chromosome

2) DNA replicated
3) Duplicated homologues pair up - crossing over takes place
4) Homologue pair line up on the spindle
5) Separation of the homologs

40
Q

What does meiosis I form?

A

2 haploid cells, with each homolog in a different cell - represented by 2 SISTER CHROMOSOMES

41
Q

How do the sex chromosomes behave together and why?

A

Behave as homologues, due to SMALL REGIONS of homology

42
Q

What is meiosis II?

A

Resembles mitosis:

1) Separation of the sister chromatids at anaphase II

43
Q

What does meiosis II form?

A

4 HAPLOID daughter cells

Each with 1 chromosome (maternal OR paternal)

44
Q

What is meiotic prophase I?

A

When the homologues pair up

45
Q

What is paring of the homologous proteins facilitated by?

A

Synaptonemal complex as well as DNA base pairing between homologues

46
Q

When does the synaptogemal complex form and what does it do?

A

Forms in prophase I to allow the homologous chromosome to line up ready for anaphase (separation)

Facilitates the genetic recombination between maternal and paternal chromosomes

47
Q

What is a chiasma?

A

The physical point of contact between the 2 non-sister chromatids of the homologous chromosome (where the crossing-over occurs)

48
Q

How many times does crossing over occur on a given chromosome?

A

Many times over the length of any given chromosome

49
Q

What is nondisjunction?

A

Gametes with an extra chromosome or lacking a homologue as the result of mistakes during meiosis I

Homologues are not separated - one daughter cell ends up with both the homologues and the other daughter cell lacks a chromosome

50
Q

What are the gametes called that arise from nondisjunction?

What does this mean?

A

Aneuploid

Don’t have the right ploidy

51
Q

What percentage of mammalian gametes are aneuploid?

A

4% sperm

20% eggs

52
Q

What is the difference between chromosomes and chromatids?

A
  • The chromosome consists of a single chromatid and is decondensed (long and string-like).
  • When DNA is copied in S phase - the chromosome now consists of two sister chromatids

BMS 242 - Advanced Cell and Molecular (24 decks)

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