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UVic BIOL 360 - Fall 2019 > Cell Cycle (ch 17) > Flashcards

Cell Cycle (ch 17) Flashcards

1
Q

What 3 processes most broadly outline the cell cycle?

A
  1. Cell growth/chromosome replication
  2. Chromosome segregation
  3. Cell division
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2
Q

Are nuclear division and cell division always linked? Please elaborate.

A

No, these processes can be independent as in drosophila melanogaster embryos.

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3
Q

How long does chromosome duplication take in humans? What about prokaryotes?

A

Humans: 10-12 hours
Prokaryotes: 20 minutes

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4
Q

How long does the mitotic phase of the cell cycle take in humans?

A

~1 hour.

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5
Q

What differentiates mitosis and cytokinesis?

A

Mitosis: duplication
Cytokinesis: splitting

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6
Q

What 4 main phases comprise the cell cycle? Which of these correspond to interphase?

A

Cell cycle: G₁, S, G₂, M

Interphase: G₁, S, G₂ only

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7
Q

What is the G₀ phase during cell division?

A

A quiescent phase which may be permanent in which a cell no longer divides or grows.

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8
Q

In yeast, the beginning of the cell division is called the “start point”. What is this called in mammals?

A

The “restriction point”.

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9
Q

After G₁, can cells go back to their pre-division state?

A

No. Once a cell has begun cell division there’s no turning back.

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10
Q

What 3 characteristics make yeast a good model organism for studying the cell cycle?

A
  1. Reproduce rapidly
  2. Very easy to do molecular analysis on
  3. Can proliferate in a haploid state
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11
Q

Why is it tricky to isolate mutants affecting the cell cycle? How do we get around that?

A

Because they continue to propagate at normal temperatures. Avoid this by growing at high temperature to arrest cell division but continue growth.

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12
Q

What 2 characteristics make Xenopus laevis embryos a good model system for studying cell division?

A
  1. Eggs are huge and easy to manipulate

2. Lots of cytoplasm means its easy to purify (to replicate cell cycle in a test tube)

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13
Q

What is the major disadvantage of using cultured mammalian cells to study the cell cycle? How do we get around this?

A

They undergo replicative senescence after ~30 replications. Avoid this by using “immortal” cell lines (cancer and viral origin).

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14
Q

What molecular methods are used to observe the cell cycle in cultured mammalian cells?

A

Specific stains (like BrdU) as well as flow cytommetry or FACS.

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15
Q

What are the 3 main characteristics of the cell cycle control system (checkpoints)?

A
  1. Binary on/off, irreversible
  2. Robust and reliable (many backups)
  3. Adaptable (cell-specificity)
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16
Q

What are the 3 cell cycle checkpoints?

A
  1. G₁/S (start) transition
  2. G₂/M transition
  3. Metaphase to anaphase transition
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17
Q

What condition must be met for the cell cycle to proceed past the G₁/S (start) transition checkpoint?

A

Environment must be favourable.

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18
Q

What 2 conditions must be met for the cell cycle to proceed past the G₂/M transition checkpoint?

A
  1. All DNA must be replicated

2. Environment must be favourable

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19
Q

What condition must be met for the cell cycle to proceed past the metaphase to anaphase transition checkpoint?

A

All chromosomes must be attached to the spindle.

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20
Q

What are the 2 major roles of cyclins during cell division?

A
  1. Activate cyclin-dependent kinase partner (Cdk)

2. Direct Cdk partner to specific target proteins

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21
Q

Outline which cyclin is active during each phase of the cell cycle.

A

G₁: G₁/S-cyclin, S-cyclin
S: S-cyclin
G₂: S-cyclin, M-cyclin
M: S-cyclin, M-cyclin

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22
Q

When does S-cyclin activity begin during the cell cycle?

A

At the “start” during the G₁ phase.

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23
Q

When does S-cyclin and M-cyclin activity end during the cell cycle?

A

At the metaphase-anaphase transition during M phase.

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24
Q

What is the function of the anaphase-promoting complex/cyclosome (APC/C)?

A

Targets cyclins for degradation.

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25
Q

How are cyclin-dependent kinases (Cdks) activated?

A

Partly active when cyclin binds to the active site. Fully active when Cdk-activating kinase (CAK) phosphorylates the active site.

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26
Q

How does Wee1 kinase affect the activity of cyclin-dependent kinases (Cdks)?

A

Adds second phosphate, which inhibits Cdk activity

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27
Q

How does Cdc25 phosphatase affect the activity of cyclin-dependent kinases (Cdks)?

A

Removes inhibitory phosphate added by Wee1 kinase, re-activating the Cdk.

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28
Q

How does a cyclin-dependent kinase inhibitor protein (CKI) function?

A

Inhibits Cdk activity by binding to both the Cdk and the cyclin.

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29
Q

What 3 things must occur for a cyclin-dependent kinase (Cdk) to activate?

A
  1. Inhibitory phosphate must be removed
  2. Activating phosphate must be present
  3. Cyclin must be bound
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30
Q

During the cell cycle, when does the Anaphase-Promoting Complex (APC/C) become active? What helps this activation?

A

Midway through mitosis at the metaphase-anaphase transition. Phosphorylation by M-Cdk can help Cdc20 bind.

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31
Q

During the cell cycle, what triggers activation of the Anaphase-Promoting Complex (APC/C)? How?

A

Binding with Cdc20 activates the APC/C.

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32
Q

Once activated during the cell cycle, what does the Anaphase-Promoting complex (APC/C) do?

A

Carries out the ubiquitylation and degradation of securins, S-cyclins, and M-cyclins.

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33
Q

What 2 main proteins is the Anaphase-Promoting Complex (APC/C) responsible for degrading?

A
  1. Securin

2. S- and M-cyclins

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34
Q

What mitotic event is triggered by the activation of the Anaphase-Promoting Complex (APC/C)? How does this happen?

A

Separation of the 2 sister chromatids. Happens when activated separase cleaves the cohesins holding the chromatids together.

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35
Q

During the cell cycle, how is separase activated? How does it cause separation of the sister chromatids?

A

The APC/C degrades securin (bound to separase), activating separase. Separase cleaves cohesins which hold the chromatids together.

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36
Q

Regarding cell cycle control, what is the purpose of the Skp/Cullin/F-Box (SCF) complex?

A

To ubiquitilate CKIs in G₁ and to degrade G₁/S-cyclins once S-phase begins.

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37
Q

Regarding cell cycle control, how does phosphorylation of a CKI affect Skp/Cullin/F-Box (SCF) activity?

A

Phosphorylation enables targeting by specific F-Box proteins.

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38
Q

How does Cdh1 activity affect the Anaphase-Promoting Complex (APC/C)?

A

It maintains APC/C activity after anaphase and throughout G₁.

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39
Q

What 2 requirements are critical for DNA replication during S phase of the cell cycle?

A
  1. DNA replication must be highly accurate

2. Every nucleotide must be replicated only once

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40
Q

Give a broad description for the S phase of the cell cycle.

A

DNA is replicated for inheritance by the two daughter cells.

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41
Q

During S phase of the cell cycle (initiation phase), what is the 1st step for DNA replication? How is this initiated?

A

Forming the prereplicative complex (pre-RC). Initiated by the APC/C.

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42
Q

During S phase of the cell cycle (Initiation phase), what is the 2nd step for DNA replication? How is this initiated?

A

Forming the preinitiation complex. Initiated by S-Cdk.

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43
Q

What 2 (sub?)phases make up the S phase of the cell cycle?

A
  1. Initiation phase

2. Replication phase

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44
Q

How is formation of the prereplicative complex (pre-RC) during S phase inhibited?

A

By Cdk activity (all about timings).

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45
Q

During the cell cycle, what holds sister chromatids together? How do these interact?

A

Cohesins. Form a ring structure around the sister chromatids.

46
Q

What are the 4 proteins which make up a cohesin (involved in the cell cycle)?

A
  1. Smc1
  2. Smc3
  3. Scc1
  4. Scc3
47
Q

What stimulates the production of cohesins which then bind the sister chromatids together during the cell cycle?

A

S-Cdk complexes, present during S phase of the cell cycle.

48
Q

What is DNA catenation? How must this be resolved?

A

The interweaving of DNA strands as a result of replication. Must be unwoven prior to strand separation.

49
Q

How is DNA catenation resolved to allow strand separation?

A

Topoisomerase II recognizes entanglement and reversibly cuts one strand to allow the other strand to pass through.

50
Q

During what phase of the cell cycle does DNA catenation occur?

A

S phase.

51
Q

What are the 5 traditional stages of mitosis?

A
  1. Prophase
  2. Prometaphase
  3. Metaphase
  4. Anaphase
  5. Telophase
52
Q

What are the 2 major parts of mitosis as divided by regulatory steps?

A
  1. Increase in M-Cdk activity

2. Metaphase-to-anaphase transition

53
Q

What happens during the first part of mitosis?

A

Assembly of mitotic spindle and attachment to sister chromatids. Nuclear pore complex is phosphorylated and disassembled.

54
Q

What happens during the second part of mitosis?

A

APC/C activation leads to chromatid separation. APC/C triggers cyclin degradation.

55
Q

What occurs in the cell during prophase?

A

Chromatin condensation.

56
Q

What occurs in the cell during prometaphase?

A

Nuclear envelope breaks down.

57
Q

What occurs in the cell during metaphase?

A

Chromosomes are aligned along the metaphase plate.

58
Q

What occurs during anaphase?

A

Sister chromatids are pulled to opposite ends of the cell.

59
Q

How is M-Cdk activated during the cell cycle? When is it activated?

A

By dephosphorylation in early mitosis.

60
Q

During prophase of mitosis, what protein complex assists in chromosome condensation? What stimulates this?

A

Condensin, which is activated through phosphorylation by M-Cdk.

61
Q

What changes occur to the number/size of microtubules as the cell is entering mitosis?

A

There is an increase in the number of shorter microtubules at the entry of mitosis.

62
Q

How are Microtubule(MT)-dependent motor proteins and MT-associated proteins (MAPs) activated during mitosis. What does this cause?

A

They are phosphorylated by M-Cdks. Triggers assembly of the mitotic spindle.

63
Q

What is the mitotic spindle during cell division?

A

A bipolar array of microtubules to separate the sister chromatids.

64
Q

What are the 3 classes of microtubules which make up the mitotic spindle?

A
  1. Astral microtubules
  2. Kinetochore microtubules
  3. Interpolar microtubules
65
Q

During mitosis, where are the astral microtubules?

A

Branching out from the centrosomes in all directions but not attaching to the kinetochore.

66
Q

During mitosis, where are the kinetochore microtubules?

A

Extending from the centrosomes and binding to the sister chromatids at the kinetochore.

67
Q

During mitosis, where are the interpolar microtubules?

A

Extending from each centrosome to bind interpolar microtubules from the other centrosome.

68
Q

Describe the function of a kinesin during mitosis.

A

Moves towards the +ve end of the microtubule, binds sister chromatids or other microtubules.

69
Q

Describe the function of a dynein during mitosis.

A

Moves towards the -ve end of the microtubule. Binds to the membrane.

70
Q

What does kinesin-14 bind to during mitosis?

A

Interpolar microtubules.

71
Q

What does kinesin-5 bind to during mitosis?

A

Interpolar microtubules.

72
Q

What do kinesin-4 and kinesin-10 bind to during mitosis?

A

Sister chromatids and kinetochore microtubules

73
Q

In what orientation are chromosomes attached to the kinetochore microtubules? Is this constant throughout mitosis?

A

Before metaphase: attached parallel

At/after metaphase: attached perpendicularly

74
Q

During mitosis, are the chromosomes always attached to the microtubule via the kinetochore?

A

No, can be connected to other parts of the chromatid.

75
Q

During mitosis, what direction will a chromatid be pulled if it is only attached to the kinetochore microtubule?

A

Towards the centrosome (-ve direction).

76
Q

During mitosis, what direction will a chromatid be pulled if it is only attached to an astral or interpolar microtubule?

A

Away from the centrosome (+ve direction).

77
Q

What is a kinetochore?

A

A complex of proteins that attaches the microtubules to the chromatid at the centromere.

78
Q

Describe the general structure of a kinetochore and how it attaches to the microtubule.

A

Like a hollow cylinder which fits on the end of the microtubule. The end comes to a point which binds to the chromatid.

79
Q

During mitosis, can a kinetochore bind to any nucleosome on the chromatid?

A

No, it must bind to a nucleosome with a centromere-specific H3.

80
Q

Why is the unique attachment method of a kinetochore to a microtubule necessary?

A

It leaves the end of the microtubule free to depolymerize as necessary.

81
Q

Give an example of a protein which is a component of a kinetochore.

A

Ndc80.

82
Q

What is meant by “incorrect attachment” of the mitotic spindle to the kinetochores on the chromatids?

A

Any deviation from each spindle pole binding to one centromere (on opposite sides of the chromatid).

83
Q

What enzyme is responsible for sensing the tension produced by correct attachment of the mitotic spindle to the kinetochores on the chromatids?

A

Kinase aurora-B.

84
Q

Under what circumstance is kinase aurora-B activated during mitosis?

A

When the mitotic spindle is improperly attached to the kinetochore on the chromatids.

85
Q

How does kinase aurora-B prevent improper attachment of the mitotic spindle with the kinetochore on the chromatids.

A

By phosphorylating the Ndc80 ends of the kinetochore to prevent attachment.

86
Q

What differentiates anaphase A from anaphase B?

A

A: driven by spindle depolymerization
B: driven by kinesin and dynein motor proteins

87
Q

What effect does phosphorylation have on replication machinery during telophase.

A

Promotes the breakdown of phosphorylated replication machinery.

88
Q

What occurs in the cell during telophase?

A

The nuclear envelope reforms and the mitotic spindle is disassembled.

89
Q

What 4 steps outline cytokinesis?

A
  1. Initiation
  2. Contraction
  3. Membrane insertion
  4. Completion
90
Q

Broadly, describe the regulation of the contractile ring formation during cytokinesis.

A

Actin-myosin ring formation regulated through activation of RhoA by RhoGEF and inactivation of RhoA by RhoGAP.

91
Q

How do higher plant cells produce two daughter cells?

A

Same as in animal cells, just split the cell with a new cell wall as well.

92
Q

In the traditional model of mitosis, when does cytokinesis begin? When does it end?

A

Begins during anaphase and ends shortly after telophase.

93
Q

Must mitosis always be paired with cytokinesis?

A

No. An example of this would be in Drosophila embryos, where mitosis occurs many times prior to cellularization.

94
Q

Must cytokinesis always involve the symetrical separation of cellular components?

A

No, sometimes the stuff inside isn’t split evenly if the daughter cells aren’t fated to be the same tissue type.

95
Q

How is cell cycle activity reset in embryonic cells which have no G₁ phase?

A

Cdc20-APC/C activity alone suppresses M-cyclin activity.

96
Q

How is cell cycle activity reset in cells which have a G₁ phase?

A

CdC20-APC/C activity initially supresses M-cyclin, and Cdh1-APC/C keeps M-cyclin activity low during G₁.

97
Q

During the cell cycle, when does Cdh1-APC/C activity increase? Why?

A

During late mitosis to suppress M-cyclin activity during the upcoming G₁ phase.

98
Q

During the cell cycle, what triggers cytokinesis?

A

Dephosphorylation of Cdk targets.

99
Q

How does a cell escape the stable G₁ phase to initiate a new cell cycle?

A

A rise in G₁/S-Cdk activity ends the suppression of other Cdk activity.

100
Q

What factor determines the size of organs and bodies? What 3 processes is this dependent on?

A

Total cell mass, which is dependent on:

  1. Cell growth
  2. Cell division
  3. Cell death
101
Q

What is a mitogen? What is their function?

A

An extracellular signalling molecule which stimulates cell division by activating G₁/S-Cdk.

102
Q

What is a growth factor? How do they function?

A

An extracellular signalling molecule which stimulates an increase in cell mass via synthesis of proteins/macromolecules.

103
Q

What is a survival factor? How do they function?

A

An extracellular signalling molecule which promotes cell survival by suppressing apoptosis.

104
Q

How many different mitogens do we know of?

A

More than 50.

105
Q

How can mitogens affect the levels of Myc in a cell? Also, what’s a Myc?

A

They can increase the levels of Myc by activating the Ras and MAPk pathways. Myc is a family of proto-oncogenes and transcription factors.

106
Q

In broad terms, outline the pathway where DNA damage can cause the inactivation of Cdks.

A

DNA damage leads to p53 activation which triggers transcription of CKI p21. This Cdk inhibitor then inactivates Cdks.

107
Q

What does a unicellular organism do if it can’t repair DNA damage?

A

It initially arrests the cell cycle, but then resumes it because it figures being mutated is worth continuing to live.

108
Q

What does a multicellular organism do if it can’t repair DNA damage?

A

Decides between having that cell undergo permanent cell cycle arrest (G₀) or apoptosis.

109
Q

What are 2 potential reasons for a cell to undergo cell cycle arrest (G₀) or apoptosis?

A
  1. Abnormal proliferation signals

2. DNA damage

110
Q

How is APC/C activated? What about SCF?

A

APC/C: Cdc20 binding

SCF: always active, targets phosphorylated proteins

111
Q

In what case is it most important to work with conditional mutations in a yeast cell?

A

When observing a loss-of-function mutation in a gene which is essential for survival.

UVic BIOL 360 - Fall 2019 (10 decks)

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