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BIOL211 Cell Biology > Eukaryotic Cell Cycle L13/14 > Flashcards

Eukaryotic Cell Cycle L13/14 Flashcards

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1
Q

Eukaryotic What needs to be equally partitioned when a cell divides into two daughter cells?

A

The genetic material

The organelles

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2
Q

In order to divide (go from G1 to S phase), cells need to receive a stimulus. What can that stimulus be?

A

Growth factors (usually)

Nutrients (sometimes, depending on cell)

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3
Q

What does the quiescence / quiescent stage refer to?

A

Gap phase, G_0

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4
Q

How long can cells remain dormant for in G_0

A

Weeks, months or even years for some cell types

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5
Q

Cells will be exposed to growth factors in what situations?

A

In response to damage, or the need to grow or repair

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6
Q

When cells produce/activate cyclin dependent kinases what happens to them?

A

Cell re-enters the cell cycle

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7
Q

What phase of the cell cycle is DNA copied?

A

G1 phase

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8
Q

When does the cell check to make sure the chromosomes have been duplicated properly?

A

G2 phase

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9
Q

How many centrosomes and copies of DNA are present in a cell in G1 phase?

A

1

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10
Q

In what phase do we get duplication of centrosomes?

A

S phase

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11
Q

When do centrosomes move to opposite poles and begin to form the mitotic spindle?

A

Moving into G2 phase

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12
Q

When do cells duplicate their DNA and organelles?

A

S phase

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13
Q

When in the cell cycle does the nuclear membrane break down?

A

G2 - M transition

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14
Q

In what phase does the mitotic spindle fully form?

A

G2 - M transition

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15
Q

When in the cell cycle do the nuclear membranes of cells reform, and the mitotic spindle collapse?

A

Telophase

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16
Q

When in the cell cycle do the centrosomes partition

A

Cytokinesis

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17
Q

What is the difference between biochemists and genetisists approach to investigating something in biology?

A

Biochemistry: Isolating factors that can recapitulate an activity in a test tube

Genetics: Genetic changes you can make to a cell’s DNA (eg; inactivating a gene) to prevent it from carrying out a process

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18
Q

What happens when you fuse an M phase cell with a cell at any other stage of the cell cycle? What does this show?

A

Spontaneous condensation of the chromosomes.

There is a soluble mitosis promoting factor in M phase cells, which forces cells into mitosis

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19
Q

What happens when you fuse an S phase cell with a G1 phase, or a cell in G2 phase? What does this show?

A

Pushes G1 cell into S phase
G2 cells don’t respond

There is a soluble factor promoting S phase entry, but can only affect G1 (temporal control)

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20
Q

What does MPF stand for?

A

Maturation Promoting Factor (Mitotis promoting factor)

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21
Q

What enzyme controls maturation of oocytes and both meiotic and mitotic divisions?

A

Maturation Promoting Factor (MPF)

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22
Q

When does MPF activity increase?

A

When progesterone is added to a G2 arrested cell

Peaks at Meiosis I (then falls)

Peaks at Meiosis II (stays high until falling after fertilisation)

Peaks at every subsequent mitosis

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23
Q

If cyclin B is not destroyed, what happens to cells?

A

They remain arrested in mitosis

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24
Q

What is cyclin B required for?

A

Mitotic entry

25
Q

What is destruction of cyclin B required for?

A

Exit from mitosis

26
Q

Why were xenopus (african tree frogs) and sea urchins used for identification of proteins required for G2/M transition?

A

Their oocytes are:

Relatively large, easy to manipulate
High protein content
Available in high numbers
Naturally synchronised
Rapid synchronous cell divisions following fertilisation

Easier to create cell extracts for biochemical analysis

27
Q

How was autoradiography used to identify cyclin?

A

Sea urchin oocytes were fertilised and 35S Methionine was added

The Methionine is only incorporated into newly produced proteins

Protein extracts were taken at different time points postfertilisation and analysed using SDS-PAGE gel

Autoradiography shows new proteins

28
Q

If cells get stuck at mitosis, what might have happened?

A

Cyclin B might not have been destroyed

29
Q

In what organism was cyclin dependent kinase identified?

A

Yeast

30
Q

What is schizosaccharomyces pombe?

A

Fission yeast

31
Q

What is S. cerevisiae

A

Budding yeast

32
Q

How can you tell if S. cerevisiae has arrested in G1?

A

They will not have a bud

33
Q

What mutant phenotype for yeast did Lee Hartwell use to identify genes required for cell progression?

A

Temperature sensitive mutants

34
Q

What are Yeast TS mutants?

A

Yeast temperature sensitive mutants, which can not grow at non-permissive temperatures

35
Q

What are non-permissive temperatures for yeast TS mutants?

A

Temperatures >35 degrees
The mutants cannot grow / replicate at higher temperatures

36
Q

What is genetic complementation?

A

Adding genes back into mutants to see which ones recover lost functions, such as certain resistances to temperature

37
Q

What are cdc mutants?

A

Cell division cycle mutants

38
Q

A plasmid containing which gene was able to rescue TS mutant budding yeast (mutant’s version of gene not working) ?

A

cdc28 (italics because its a gene)

39
Q

What does SPF stand for?

A

S-phase promoting factor

40
Q

What is SPF required for?

A

SPF is critical to bypass the G1/S phase transition. (Bypass restriction point [mammals] and START [yeast])

41
Q

What is MPF required for?

A

MPF is critical to bypass the G2/M phase transition

42
Q

What does cdc28 code for?

A

A cyclin dependent kinase

43
Q

What is the name of the point cells decide to go from G1 to S phase in mammalian cells and in yeast cells?

A

Mammalian: Restriction point

Yeast: START

44
Q

As well as growth factors, what do yeast require to divide?

A

Sufficient nutrients in their environment

45
Q

How does the TS mutation for cdc28 affect the cyclin dependant kinase?

A

Affects protein stability, making it more susceptible to thermal denaturation

Affects kinase’s affinity for cyclin (which it depends on for activation), and at high temperatures they dissociate -> loss of kinase function

46
Q

How did increasing abundance of G1 cyclin (overexpression) rescue the cdc28 phenotype and lead to identification of the cyclin dependent kinases?

A

More cyclins meant the kinases were more likely to form complexes and activate, despite their instability (from low affinity)

This allowed complementation, and therefore identification of the presence of cyclin dependent kinases

47
Q

Compare the variation in kinases and cyclins throughout the cell cycle

A

Only one kinase is used through the cell cycle, but each phase of the cell cycle is regulated by different cyclins

48
Q

How can you tell through cell morphology what stage of the cell cycle fission yeast is in?

A

The length of the cell

49
Q

Cdc mutants in S. pombe identified arrest at which stage of the cell cycle?

A

G2/M transition

(They were long cells)

50
Q

Gene complementation for identifying cell cycle regulators was performed for the _______ using the gene library previously used for the _______ .

A

S. pombe (Fission yeast)

S. cerevisiae (Budding yeast)

51
Q

A plasmid containing which gene was able to rescue TS mutant fission yeast (mutant’s version of gene not working) ?

A

cdc2 (italics because its a gene)

52
Q

The cyclin dependent kinase controls what in budding yeast and fission yeast? What does this show?

A

G1/S transition in budding yeast
G2/M transition in budding yeast

G2/M transition in fission yeast

Shows there is a functionally conserved kinase across both yeasts, and potentially in higher eukaryotes

53
Q

What are the names of the conserved cyclin dependent kinase in budding yeast, fission yeast, and humans?

A

Budding: Cdc28
Fission: Cdc2
Human: CDK1

54
Q

What is the phenotype of a cdc2- (knockout for cdc2)?

A

Cell is unable to enter mitosis
Cell growth continues, resulting in overlarge cells

55
Q

What happens if cdc2 cannot be phosphorylated?

A

Cells enter mitosis rapidly (force cells into mitosis (similar to MPF))
Cell growth is insufficient, causing very short cells (wee phenotype)

56
Q

What is cdc^D?

A

Constitutively active cdc2 where a negatively charged amino acid is put in phosphorylation site, preventing the kinase from being phosphorylated

57
Q

What regulates mitotic CDK?

A

Cyclin binding

Wee 1 kinase (adds phosphates)
Cdc25 phosphatase (removes phosphates)

58
Q

What affect on mitosis does having a deficit of Cdc25 or excess of Wee1 have?

A

Prevents mitosis
Elongated cells (due to increased G2)

59
Q

What affect on mitosis does having an excess of Cdc25 or deficit of Wee1 have?

A

Inappropriate mitosis
Small cells (decreased G2)

BIOL211 Cell Biology (19 decks)

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