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CBFM - M1T1 > Cell Cycle > Flashcards

Cell Cycle Flashcards

1
Q

What is a CKI?

A

Cyclin kinase inhibitor

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2
Q

What term describes cells that are in a reversible G0 phase?

A

Quiescent

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3
Q

What checkpoint initiates entry into the cell cycle and is considered the “starting point?”

A

Restriction Point in G1 - Sensitive to the size of the cell, physiological state, and environmental factors

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4
Q

When does the spindle assembly checkpoint take place?

A

M phase, between metaphase and anaphase. A negative signal from a kinetochore blocks APC-cdc20 activation and separation of sister chromatids.

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5
Q

True/False. Cells in G0 are not replicating, but are still metabolically active.

A

True

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6
Q

How does Rb control the R checkpoint?

A

Rb binds and inhibits transcription factor E2F, which is needed to transcribe genes for S- and G1-CDKs. When a cell is stimulated by mitogens, Rb is phosphorylated and inactivated.

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7
Q

What signals are used to control cell checkpoints?

A

Negative intracellular signals

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8
Q

How is CDK activity relguated?

A
  1. Combination with different cyclins
  2. Phosphorylation/dephosphorylation
  3. Binding of inhibitory subunits
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9
Q

What is the mitotic spindle composed of and where does it originate?

A

Composed of microtubules that form near the centrosomes in prophase

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10
Q

What takes place during metaphase?

A

Sister chromatids line up on the metaphase plate and mitotic spindles begin attaching to kinetochores. A trial and error approach ensures correct attachment to sister chromatids and appropriate tension.

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11
Q

In this step of mitosis, sister chromatids condense and prepare for separation and the mitotic spindle begins to form.

A

Prophase

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12
Q

What is the function of G1/S and G2/M checkpoints?

A

Check for DNA damage. Damage is repaired or the cell undergoes apoptosis.

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13
Q

These cells lack the machinery necessary for mitosis (ex: RBCs).

A

Terminally differentiated

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14
Q

In what phase do most cells spend the majority of their time?

A

G0

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15
Q

What is the cellular response to continued high levels of c-Myc?

A

Excessive c-Myc activates p53 to stop the cell cycle.

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16
Q

Cells that have irreversibly exited the cell cycle due to aging, shortened telomeres, or DNA damage are called what?

A

Senescent

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17
Q

What is the role of growth factors in cell division and proliferation?

A

While growth factors do not stimulate cell proliferation, they do increase cellular uptake of nutrients and biosynthetic pathways. This is essential for cells to grow and thus divide.

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18
Q

What protein competes with c-Myc for binding to limit cell growth and proliferation during differentiation?

A

Mad

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19
Q

What protein acts as a tumor suppressor and is required to arrest cells with DNA damage in G2 for a prolonged period?

A

p53

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20
Q

What occurs in S phase of the cell cycle?

A

DNA Replication

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21
Q

What process takes place in G1 that is essential for DNA synthesis in S phase?

A

DNA Licensing by ORC-Mcm complex

22
Q

Phosphorylation is important in regulation of which CDK?

A

M-CDK

23
Q

What is the effect of active site phosphorylation on CDK activity?

A

Phosphorylation of CDK at the active site inhibits CDK activity. Dephosphorylation by a phosphatase restores CDK activity.

24
Q

In this stage of mitosis, the mitotic spindle disassembles and the nuclear envelope begins to reassemble. M-CDK and S-CDK have been degraded.

A

Telophase

25
Q

How are sister chromatids separated during anaphase?

A

APC ubiquitin ligase is bound by cdc20 and activated. The ligase degrades securin, which inhibits activity of separase. Separase then cleaves cohesions holding sister chromatids together.

26
Q

What enzyme initiates and regulates the cell cycle?

A

Cyclin-dependent kinases

27
Q

During this stage of mitosis, sister chromatids separate and kinetochore microtubules get shorter.

A

Anaphase

28
Q

True/False. In the abscene of DNA damage, p53 is quickly degraded by a ubiquitin ligase.

A

True. When DNA damage is identified, protein kinases phosphorylate p53 and decrease its affinity for the ubiquitin ligase.

29
Q

How does p53 faciliate DNA damage repair and cell apoptosis.

A

p53 is a transcription factor.

Binds the regulatory region of p21 to promote transcription. p21 inhibits CDK.

Promotes transcription of DNA repair factors

Promotes transcription of apoptosis genes

30
Q

What cell cycle checkpoint delays onset of chromosome segregation until all chromosomes are appropriately attached to the mitotic spindle?

A

Spindle assembly checkpoint

31
Q

How are CDKs activated?

A

Cdk becomes partially active when bound to cyclin, but must be phosphorylated by CAK to become fully active.

32
Q

These signal factors promote cell growth, but not proliferation, through synthesis of macromolecules.

A

Growth factors

33
Q

The transcription factor c-Myc increases synthesis of…

A
  • G1 cyclin
  • Subunit of ubiquitin ligase
  • Transcription factor E2
34
Q

What protein controls the restriction checkpoint?

A

Retinoblastoma protein (Rb)

35
Q

During cytokinesis, the cytoplasm is divided into two contractile rings that pinch the cell into two daughters. What composes the contractile ring?

A

Actin & myosin filaments

36
Q

What phosphatase activates M-Cdk by dephosphorylation?

A

cdc25

37
Q

In addition to degrading securin in mitosis, the activated APC-cdc20 complex also serves what function?

A

Degrades M and S cyclins to allow the cell to exit mitosis.

38
Q

What is the function of M-CDK?

A

Induces assembly of the mitotic spindle and ensures attachment by replicated chromosomes

39
Q

What stimulates the passage through the R checkpoint in G1?

A

Mitogens - cells without appropriate stimulation fail to enter the cell cycle.

40
Q

Describe cellular levels of M-Cdk during G2 and M phases.

A

During much of G2, M-Cdk levels slowly rise, but are kept inhibited by phosphorylation of the active site. In late G2, M-Cdk accumulates and the inhibitory kinase can no longer keep up. Active M-Cdk then phophorylates cdc25, which goes on to dephosphorylate inactive M-Cdk for activation.

41
Q

What is the purpose of the G1 phase of the cell cycle?

A

Cell growth, environmental monitoring, restriction point, check for DNA damage

42
Q

What is the role of c-Myc in passage through the R checkpoint?

A

c-Myc is an immediate-early gene activated by mitogen stimulation. c-Myc activates transcription of delayed response genes, such as G1 cyclins, which later inactivate the Rb protein through phosphorylation.

43
Q

What is the primary mechanism regulating CDK activity?

A

Changing cyclin levels via ubiquitination

44
Q

These signal factors inhibit apoptosis to promote survival.

A

Survival factors

45
Q

G1 and S phase CDKs are regulated primarily by what method?

A

Binding of inhibitory subunits

46
Q

True/False. All cells are fully mitotic.

A

False. Some cells are fully mitotic, such as germ cells, lymphocytes, and keratinocytes. Other cells are semi-mitotic, such as liver cells and visual cells. Highly specialized, such as heart cells, brain cells, and RBCs, lack mitotic ability.

47
Q

The G1/S-CDK is composed of what cyclin subunit?

A

Cyclin E

48
Q

Cyclin A composes what cyclin-CDK complex?

A

S-Cdk

49
Q

M-Cdk, required for entry into mitosis, is composed of what cyclin?

A

Cyclin B

50
Q

What cyclin composes G1-Cdk and is required for transition through the G1/S checkpoint?

A

Cyclin D

CBFM - M1T1 (42 decks)

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