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BMS242 Cell and Molecular > L7 - Mitosis and Meiosis > Flashcards

L7 - Mitosis and Meiosis Flashcards

1
Q

Why must the rates of cell division be carefully controlled

A

To regulate the cell numbers in a given tissue

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2
Q

How many division every 24 hours - typically

A

1

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3
Q

What cells don’t divide any more

A

Terminally differentiated cells

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4
Q

What are the two phases of M phase

A

Divison of the nucleus

Division of the cytoplasm

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5
Q

What happens in S phase

A

DNA synthesis

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6
Q

What occurs at prophase

A

Condensation of the sister chromatids

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7
Q

What occurs at metaphase

A

Attachement of the mitotic spindle to the kinetochore

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8
Q

What occurs at anaphase

A

Separation of the sister chromatids

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9
Q

What are the two types of yeast lifecycle

A

Budding and fission

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10
Q

What is significant about yeast undergoing a budding lifecycle

A

No G2 phase

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11
Q

What is significant about yeast undergoing a fission lifecycle

A

Short G1 phase

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12
Q

What forms as the result of a budding lifecycle

A

Forms separate daughter cells one of which is smaller and buds off

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13
Q

What forms as a result of the fission lifecycle

A

Divides an stays together forming filaments

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14
Q

What are the advantages of using Yeast as a model organism to study the cell cycle

A

Rapid division rate
Cell cycle control genes are highly conserved
Yeast can be grown as haploid or diploid

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15
Q

What is a genetic trick to do with the fact that yeast can be grown as haploid and as diploid

A

Diploids are used to maintain lethal muations that are studied in haploids
Knock out one copy of the gene - then turn into a haploid and study

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16
Q

What are temperature sensitive mutations

A

At a low tempature the protein is functional - when the temperature is increased there is no further function of the protein

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17
Q

What can temperature sensitive mutations be used for

A

To arrest cells at a particular stage of the cycle and then to synchronise these cells at a stage

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18
Q

What are the genes controlling cell division known as

A

Cell cycle control genes - Cdc genes

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19
Q

Advantages of using the Xenopus to study the cell cycle

A

Well known // Well studied lifecycle
Rapid division rate (every 30 mins)
Large size - easier to purify proteins
Manipulation by injection of RNAs/chemical into the oocyte

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20
Q

Describe the three requirements for cell free mitosis

A

Cyctoplasm from a frogs egg
Nucleus from the sperm of a frog
ATP

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21
Q

What are two uses of the cell free mitosis technique

A

Deplete the cytoplasm of proteins using antibodies

Remove cytoplasm at any stage to study changes e.g to protein phosphorylation over time

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22
Q

What are the three checkpoints of the cell cycle

A

G1/S (start)
G2/M
Metaphase-anaphase trnasition

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23
Q

G1/S transition

A

Is the environment favourable

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24
Q

G2/M transition

A

Is all of the DNA replicated

Is the environment favourable

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25
Q

What is checked at the metaphase - anaphase transition

What type of signalling is used?

A

Check if all of the chromosomes are attached to the spindle

Negative signalling

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26
Q

When does G1/S cyclin peak

A

Once cell pases G1/S (start) and commits to division

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27
Q

When does G1/S cyclin levels fall to the min level

A

At the end of G1 phase

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28
Q

When do s-cyclin levels peak

A

During S and G2 phase

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29
Q

When do s-cyclin levels fall

A

At the beginnig of M phase

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30
Q

When do m-cyclin levels rise

A

During G2 and M phases

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31
Q

Cyclins are proteins which

A

Are expressed at different levels during different stages of the cell cycle

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32
Q

What do cyclins bind

A

Cdk

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33
Q

What do cdks do

A

Phosphorylation of target proteins which are specific to certain stages of the cell cycle

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34
Q

How many phosphate groups req for activation

A

1

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35
Q

When a second phosphate group is added onto a cdk what occurs

A

Inhibition and inactivation

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36
Q

What enzyme removes a phosphate group from CDK

A

Cdc25 phosphatase

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37
Q

What enzyme adds a phosphate group from CDk

A

Wee1 kinase

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38
Q

What is the effect of p27

A

Binds to CDK-cyclin forming p27-cdk-cyclin complex which causes inactivation

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39
Q

What are the two sub units which must combine for the active APC/C complex to form

A

Inactive APC/C and Activating subunit cdc25

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40
Q

What is the anaphase promoting complex

A

A ubiquitin ligase

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41
Q

What does the APC/C do

A

Adds a polyubiquitin chain to M-cyclin ==> leads to degredation of m-cyclin by the proteasome
Also ubiquitinates S-cyclin and securin

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42
Q

What is the role of securin

A

Holds the sister chromatids together `

43
Q

What is also required by the APC/C for the ubiquitination of M-cyclin

A

Ubiquitination enzymes E1 and E2 and ubiquitin

44
Q

A favourable EC environment activates

A

G1-CDK

45
Q

G1-CDK activates … which then activates

A

G1/S cyclin synthesis

S Cyclin synthesis

46
Q

S cyclin activates …

A

s-cdk

47
Q

What does DNA damage inhibit

A

G1/S CDK
S-CDK
M-CDK

48
Q

Unreplicated DNA inhibits

A

M-CDK

49
Q

Unattached chromsomes inhibit

A

APC/C

50
Q

What does diploid mean

A

Have two copies of each chromosomes which are known as homologous chromosomes either maternal or paternal

51
Q

Meiosis is similiar to mitosis except for …

A

There must be extra steps to separate homologous chromosomes

52
Q

What does the pairing of homolgous chromosomes before segregation allow

A

Crossing over - homologous recombination

53
Q

Do the X and Y chr behave as homologous chr

A

Behave like homologous due to small regions of homology

54
Q

During meiosis prophase I what is crossing over aided by

A

Synaptoneal complex as well as DNA base pairing between homologes

55
Q

What does homologous recombination between non sister chromatids serve

A

Aligns chromosomes ready for anaphase and aids in the formation of the synaptoneal complex
Allows for genetic recombination between paternal and maternal chromosomes

56
Q

Where does crossing over occur

A

Chiasma

57
Q

What occur where chr missing/added to a cell

A

Called non disjunction

Any gametes that arise are aneuploid

58
Q

How many mammalian sperm aneupoloid

A

4%

59
Q

How many mamalian eggs are aneuploid

A

20%

60
Q

What is the purpose of regulating the rate of division in cells and tissue

A

Enables you to maintain cell numbers in each tissue

61
Q

How often to mammalian cells divide on average

A

Every 24 hours

62
Q

During DNA duplication, each chromosome pair (maternal and paternal) is duplicated to give rise to sister chromatids, T or F

A

T

63
Q

Sister chromatids are then segregated between the two daughter cells, T or F

A

T

64
Q

What is meant by G­1 phase and what is going on the cell during this phase

A

G1 or gap 1 phase is the phase in which most cells are in. The cell is growing and constantly checking its environment. This growth is required to maintain cell size with subsequent divisions.

65
Q

What is G0 phase

A

A quiescent, non-dividing phase

66
Q

What is the restriction or start point

A

A point in the cell cycle after G1 phase that determines the commitment of the cell to S phase and the completion of the rest of the cycle to G1 again

67
Q

What happens during G2 phase of the cell cycle

A

More growth of the cell and environmental checking. It has a shorter duration than G1 phase

68
Q

What are the constituent parts of M phase

A

Nuclear division – mitosis and cytoplasmic division (cytokinesis)

69
Q

What are the stage of mitosis

A

Prophase, prometaphase, metaphase, anaphase and telophase

70
Q

During which stage of mitosis do the chromosomes attach to the mitotic spindle via their kinetochores and the microtubules

A

Metaphase

71
Q

During which phase of mitosis do the sister chromatids condense

A

Prophase

72
Q

What happens during anaphase

A

Sister chromatids are separated

73
Q

Telophase corresponds to cytokinesis, T or F

A

T

74
Q

What can be said about the genes that control the cell cycle

A

They are extremely conserved and almost identical across the species

75
Q

What are the two different types of yeast models

A

Fission yeast and budding yeast

76
Q

What are the advantages of using yeast to study the cell cycle

A

Rapid division rate <1hr, cell cycle control genes almost identical to human, can be grown as haploids or diploids

77
Q

How can the ability of yeast to be haploid or diploid be harnessed to study the cell cycle

A

If you want to study a gene involved in cell cycle, manipulation will have a very deleterious effect on that organism. If you have carriers of the deleterious gene in diploid state and then switch the yeast to haploid when you want. Thus, diploids can be used to maintain lethal mutations that are then studied as haploids

78
Q

How can you use temperature sensitive mutations in yeast to study the cell cycle

A

You can introduce mutations that only disrupt gene functions at particular temperatures into the yeast. Keeping the yeast at a low permissive temperature maintains gene function but switching to a restrictive (high) temperature enables you to study the genes function

79
Q

What are the advantages using Xenopus laevis as a biochemical model when looking at the cell cycle

A

Easy to collects its eggs, rapid division rate, large sized eggs makes protein purification easier and they can be manipulated by injection of RNA or chemicals into the oocytes

80
Q

What is cell-free mitosis

A

Technique that allows you to observe mitosis/nuclear division in a test tube outside of the cell membrane. This can be used to study changes i.e. in protein phosphorylation over time after cytoplasmic depletion using antibodies

81
Q

What is the role of the start checkpoint

A

Checkpoint at the end of G1 that checks to see if the environment is favourable before triggering the DNA replication machinery to replicate the DNA. It ensures that the cells have enough resources to go through the cell cycle to G1 again

82
Q

What is the purpose of the G2/M checkpoint

A

Checks to see is all DNA has replicated and if the environment is favourable before assembling the mitotic machinery

83
Q

What happens at the metaphase to anaphase transition

A

Cell checks that all the chromosomes are attached to the mitotic spindle before triggering anaphase and completing cell division

84
Q

Cyclins are a class of protein involved in the regulation of the cell cycle, explain how they interacts with their targets

A

Cyclins bind to cyclin-dependant kinases (Cdks) to activate them

85
Q

What are Cdks and how do they act

A

Cyclin dependant kinases (Cdks) are kinases that phosphorylate proteins involved in specific stages of the cell cycle

86
Q

Give examples of different cyclins and how they act with Cdks at different times in the cell cycle

A

M-cyclin is high during mitosis and the Cdk-M-cyclin complex leads to phosphorylation of protein involved in the assembly of the mitosis machinery. Whereas S-cyclin is high during S phase and the Cdk-S-cyclin complex phosphorylates proteins involved in the assembly of DNA replication machinery

87
Q

Cyclins are expressed at constant levels during the cell cycle, T or F

A

F – cyclins are transiently expressed and are synthesised and degraded throughout the cell cycle

88
Q

Levels of Cdk remain constant throughout the cell cycle, T or F

A

T

89
Q

Cdks require cyclin to become active, T or F

A

T

90
Q

How are Cdks further regulated other than the action of cyclins

A

Cdks are also regulated by their phosphorylation state. Active Cdk contains 1 phosphorylated serine residue whereas inactive Cdk has 2 phosphorylated serine residues. Unusually phosphorylation is an inhibitory signal in the case of Cds.

91
Q

Explain the enzymes involved in the regulation of Cdk activity

A

Wee1 kinases is responsible for the phosphorylation and inactivation of Cdk. Whereas Cdc25 phosphatase removes a phosphate group from the inactive Cdk hence activating it. The interplay between Wee1 kinase and Cdc25 phosphatase determines that activity of Cdks.

92
Q

What is the name of the protein inhibits the activity of the cyclin-cdk complex

A

p27

93
Q

What is the name of the complex that marks cyclins for degradation and how is this achieved

A

Anaphase promoting complex (APC) marks cyclins for degradation by ubiquitination

94
Q

What is the main difference between meiosis and mitosis

A

Meiosis resembles mitosis except there are extra steps that segregate homologous chromosomes

95
Q

Pairing of homologues before segregation allows for crossing-over via homologous recombination, T or F

A

T

96
Q

In meiosis I sister chromatids aren’t separated, what does happen during this stage

A

Homologous chromosomes pair up and crossing over takes place. These cells will be haploid with each homologue represented by two sister chromatids

97
Q

Sex chromosomes don’t cross over, T or F

A

F – they behave like homologues during sperm formation due to small regions of homology

98
Q

What happens during meiosis II

A

Chromosomes line up on the metaphase plate and sister chromatids are separated

99
Q

Explain how pairing of chromosomes is facilitated in meiotic prophase I

A

Pairing is facilitated by the synaptonemal complex as well as DNA base pairing between homologues

100
Q

What are the two purposes of homologous recombination between non-sister chromatids

A

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

101
Q

Mistakes during meiosis I result in gametes with an extra chromosome or lacking a homologue, what is the name given to this event

A

Nondisjunction

102
Q

How are the cells that arise from gametes that contain an extra chromosome or missing homologue referred to

A

Aneuploid

103
Q

What percentage of mammalian sperm and eggs contain extra chromosomes or missing homologues

A

4% of sperm, 20% of eggs

BMS242 Cell and Molecular (26 decks)

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