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Cell Cycle Flashcards

1
Q

What two stages of the cell cycle are encompassed by the M phase?

A

Mitosis and cytokinesis

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2
Q

What is the collective name for the G1, S and G2 phases?

A

Interphase

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3
Q

Which phase of the cell cycle is the longest and which the shortest?

A

Longest - G1

Shortest - M

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4
Q

How can cells in the G0 phase re-enter the cycle?

A

These cells can reenter the cycle open stimulation by mitogens

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5
Q

What is the name of the G1 checkpoint?

A

Restriction Point

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6
Q

Cdk concentration fluctuates throughout the cell cycle whereas cyclin concentration is constant. T/F?

A

False - the opposite is true

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7
Q

What are the two functions of S-Cdk complexes?

A

To phosphorylate proteins to initiate helix unwinding, thus preparing for DNA replication
To prevent re-initiation of DNA replication at the same origin during the same cycle

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8
Q

How are cyclin-Cdk complexes deactivated?

A

Specific enzyme complexes add ubiquitin chains to cyclins that label them for destruction in the proteasome.

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9
Q

Why is it important that cells grow in between cell divisions?

A

Cells must at least double in size so that the daughter cells are not smaller than the mother cell upon division of the cytoplasm.

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10
Q

What is checked at the M checkpoint?

A

That chromosomes are correctly aligned on the metaphase plate and attached to spindles

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11
Q

What is checked at the G1 checkpoint?

A

The G1 checkpoint ensures that growth conditions are favourable and that DNA is undamaged

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12
Q

What is checked at the G2/M checkpoint?

A

This checkpoint ensures that DNA is replicated and undamagaed

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13
Q

Where on the chromosome is DNA replication initiated?

A

The origin of replication.

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14
Q

After DNA replication the two sister chromatids are tightly bound together by…?

A

Cohesion rings

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15
Q

What type of cells remain in the G0 phase for the entirety of their mature lifetime?

A

Neurons

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16
Q

At what point does the cell no longer require the presence of growth factors?

A

Following the G1 checkpoint

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17
Q

How does DNA damage prevent the cell from entering S phase?

A

DNA damage causes an increase in p53 concentration. p53 is a transcription regulator which activates the transcription of p21 which inhits G1/S-Cdk and S-Cdk. These cyclin- pCdk complexes guard the restriction point and their inhibition prevents the cell from passing into S phase.

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18
Q

Following DNA damage, if DNA cannot be repaired what process will be initiated by p53?

A

Apoptosis

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19
Q

During apoptosis changes are made in terms of glycosylation and receptor expression of the cell. Why is this important?

A

This facilitates recognition and engulfment by macrophages.

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20
Q

What are the two components of Maturation promoting factor?

A

Cyclin B and Cdk 1

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21
Q

What are the three functions of Maturation promoting factor?

A

Initiate chromosome condensation
Promote breakdown of nuclear membrane
Initiate assembly of mitotic spindle

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22
Q

The phosphorylation of which set of proteins leads to the condensing of chromosomes?

A

Condensins

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23
Q

What is the mitotic spindle composed of?

A

Microtubules and their associated motor proteins

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24
Q

What is the contractile ring composed of and where is it situated?

A

It is composed of actin and myosin filament which form a ring around the cell that assembles just beneath the plasma membrane.

25
What occurs during prophase?
The replicated chromosomes condense and the mitotic spindle begins to form outside the nucleus.
26
What happens in prometaphase?
The nuclear membrane breaks down and spindle microtubules attach to the chromosomes.
27
What happens in metaphase?
The mitotic spindle gathers the chromosomes so that they line up on the equator of the cell
28
What happens during anaphase?
The two sister chromatids are synchronously pulled apart and the spindle draws them to opposite poles of the cell.
29
What happens during telophase?
The nuclear reassembles around each of the two sets of chromosomes to form two new nuclei.
30
What is cytokinesis and when does it take place?
Cytokinesis is the splitting of the cytoplasm into two new daughter cells that begins in anaphase and continues through to telophase
31
When does centrosome duplication begin and what triggers this?
Duplication begins at the start of S phase and is triggered by the same cyclin-kinase complexes that trigger DNA replication (G1/S-Cdk and S-Cdk)
32
What is meant by the description of the mitotic spindle as 'dynamically instable'?
The microtubules can depolymerize and polymerize rapidly so as to grow and shrink
33
How is the basis of the mitotic spindle formed?
Some of the microtubules from opposite poles will join together to increase their stability, this forms the basis of the mitotic spindle.
34
What triggers the dissolving of the nuclear membrane in mitosis?
Phosphorylation and consequent disassembly of nuclear pore proteins and intermediate filament proteins of the lamina. The phosphorylation of the lamins is done by kinase C and cyclin A activated Cdk 1.
35
To which protein complex do spindle microtubules attach?
The kinetochore
36
When and where does the kinetochore assemble and what is its assembly dependent on?
The kinetochore assembles on the centromere of replicated chromosomes during late prophase and their assembly is dependent on the centromere DNA sequence.
37
How is separase kept inactive until the start of anaphase?
By binding to the inhibitory protein securin
38
What targets securin for destruction at the start of anaphase?
Anaphase-Promoting Complex (APC)
39
APC can target M cyclin for destruction. What effect does this have?
M cyclin destruction inactives the M-Cdk complex and drives the cell out of mitosis
40
What happens in Anaphase A?
Kinetochore microtubules shorten by depolymerisation.
41
What happens in anaphase B?
Spindle poles move themselves further apart.
42
How is the nuclear membrane reformed?
By the dephosphorylation of nuclear pore proteins and nuclear lamins.
43
What structure, positioned perpendicular to the long axis if the mitotic spindle, ensures each daughter cell receives one copy of the full chromosome set?
Cleavage furrow
44
The Bcl2 family of proteins are important in mitosis. Give examples of these proteins which inhibit apoptosis and examples of those which promote apoptosis.
Inhibit - Bcl-2 and Bcl-X1 Promote - Bax and Bak
45
Why must cells duplicate in size before they divide?
To ensure that the daughter cells are not smaller than the parent cells
46
With which cyclin do Cdk 4 and Cdk 6 bind to at the start of G1?
Cyclin D
47
With which cyclin does Cdk 2 bind to at the end of G1 phase?
Cyclin E
48
With which cyclin does Cdk 2 bind with in S phase?
Cyclin A
49
With which cyclin does Cdk1 bind to at the end of G2?
Cyclin A
50
CDk 1 combines with which cyclin in M phase?
Cyclin B
51
Following which point in the cell cycle does the cell no longer require growth signals and is unresponsive to antimitogenic signals?
Restriction point
52
How does an increase in the activity and concentration of p53 in response to DNA damage lead to cell cycle arrest?
P53 is a transcription regulator that activates the transcription of p21. P21 is an inhibitor protein which binds to the cyclin-CDK complexes present in G1 to prevent the cell from going into S phase.
53
Why would a cell be stopped from entering M phase?
Because there is NA damage or because DNA is not completely replicated
54
Describe how the protein myc functions to cause apoptosis.
It is a transcription factor which activates the expression of many genes involved in cell proliferation but can down regulate Bcl2 to cause apoptosis
55
Cyclin dependent kinase inhibitors are small molecules which block cyclin/CDK activity either by forming an inactive complex or by acting as a competitive CDK ligand. Give examples of these inhibitors?
p21 CIP p27 KIP p16 INK
56
Which cyclin/CDK complex is known as maturation promoting factor?
Cyclin B and CDK1
57
What is the action of maturation promoting factor which allows progression to M phase?
Nuclear enveloped destroyed by phosphorylation of lamins Chromosome condensation Spindle formatiom
58
What is a cell cycle checkpoint?
A point in the eukaryotic cell division cycle where progress through the cycle can be halted until conditions are suitable for the cell to proceed
59
Cell monitoring occurs at checkpoints in the cell cycle. What can be monitored?
``` Favourable external and internal environment DNA damage Replication errors Spindle formation Chromosome integrity ```

Cell Biology (6 decks)

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