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CBG Replication,transcription translation > 9-cell cycle > Flashcards

9-cell cycle Flashcards

1
Q

what happens in M phase? are chromosomes visible?

A

Mitosis/meiosis and cytokinesis. (chromosomes are splitting and visible under microscope)

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2
Q

what happens in S phase?

A

Dna synthesis

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3
Q

how much more growth is there in G2 in comparison to G1?

A

double amount of dna

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4
Q

what type of hydrogen was used in experiments on s phase?

A

radioactive H3 thymidine Tritium hydrogen

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5
Q

What is needed for DNA synthesis that is not ATP and allowed the S experiments to take place?

A

H3 radioactive hydrogen could be incorporated in TTP which would be taken up in DNA synthesis.

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6
Q

How did they confirm cells where in S phase half of the cell cycle time?

A

Autoradiograph showed half of the cells took up labelled TTP and so we can assume the cycle is in s phase half its time

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7
Q

how were G1 and G2 investigated?

A

flow cytometry

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8
Q

How does flow cytometry work to investigate G1 and G2?

A

a single cell with dye added and this binds to DNA and then measure DNA concentration G1-1/2 fluorescence of G2 G2- double flourescence of G1 this enabled estimation of time spent in G1 and G2

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9
Q

what did injection studies in oocytes show?

A

cell cycle affected by external factors such as hormones

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10
Q

What has progesterone got to do with frog oocytes?

A

progesterone was injected into frog oocytes and induced M phase then this M phase cytosol was injected to G2 phase cytosol which was then induced to go into M phase.

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11
Q

What is the secondary thing the frog oocyte experiment showed?

A

M phase cytosol injected into G2 phase induced G2 phase to go into M phase (something in M forces G2 to go to M)

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12
Q

what were the Hela cells used for?

A

Fusion experiments, the fused different cells in different phases of the cell cycle to see the effects.

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13
Q

what happens when s phase and G1 cells fuse?

A

All go into s phase. S phase contains factors that can diffuse to other nucleus and lead G1 cell to replicate DNA and enter s phase (this is visible due to use of thymidine which becomes incorporated)

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14
Q

What combination of cells leads to no change to either?

A

S phase and G2 phase. G2 is refractory and cannot be induced by s factors.

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15
Q

what is interphase made up of?

A

G1,S,G2

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16
Q

what happens when interphase cells (G1,S,G2) are fused with cells in M phase?

A

all cells enter M phase. mitotic cells forced all others to go into mitosis. This was assumed because all chromosomes then condensed.

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17
Q

what happens when G1 and G2 cells are fused together?

A

G2 loses s phase factors

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18
Q

what did budding yeast temperature sensitive mutants show?

A

They arrested(stalled) at G1 when exposed to high temperatures which revealed a first checkpoint: is my DNA damaged? (possible G0 arrest phase)

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19
Q

what yeast was used in the budding experiments?

A

saccharomyces cerevisiae Cdc28

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20
Q

what type of factors are the 3 main checkpoints regulated by? (2)

A

external and internal

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21
Q

what are the 3 checkpoints?

A

1)restriction point/start (G1) 2)G2/M 3)M

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22
Q

how is progress of the cell cycle affected by cyclins?

A

progress of cell cycle is dependent on most abundant cyclin at the time

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23
Q

what do cyclins do?

A

tell cyclin dependent kinase what to do: genes to activate,switch off,proteins to make etc)

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24
Q

what does CDK stand for?

A

cyclin dependent kinase

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25
Q

why do the mutant yeasts arrest?

A

faulty dependent kinase

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26
Q

at what stages do s-type cyclins increase in concentration?

A

G1/s/G2

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27
Q

at what stages of the cell cycle do s-type cyclin levels drop?

A

G2/M2

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28
Q

where does the sudden change from high conc to low conc occur,what cell phase?

A

G2

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29
Q

who discovered cyclins and whilst studying what?

A

They were discovered by R. Timothy Hunt in 1982 while studying the cell cycle of sea urchin

30
Q

what are cyclins?

A

a family of proteins that control the progression of cells through the cell cycle by activating cyclin-dependent kinase (Cdk) enzymes

31
Q

what do cyclins form once bound to dependent kinases?

A

maturation-promoting factor (MPFs)

32
Q

what do MPFs activate and how?

A

MPFs activate other proteins through phosphorylation

33
Q

What are the 4 main cyclin classes?

A

G1/S cyclins, S cyclins, G2 cyclins, M cyclins.

34
Q

what cyclin type is involved in the checkpoint that promotes passage through the start?

A

G1/S cyclin

35
Q

How many CDKs are there in yeast?

A

1 (but there are several in humans)

36
Q

in which phase is the restriction point/start point?

A

in G1

37
Q

what is the restriction point/start point deciding?

A

should cell divide?should division be delayed/should cell enter resting stage?

38
Q

what does checkpoint of G2 about to go to M (G2 checkpoint) try do decide?

A

it is assessing success of DNA replication and whether to trigger start of M phase

39
Q

what does checkpoint M decide?

A

assesses accuracy of mitosis (during metaphase) and triggers mitosis exit and beginning of G1

40
Q

what cyclins are involved in start G1 checkpoint and by what mechanism are they acting?

A

CDK+G1 cyclin & CDK+G1/S cyclin promote passage through start by phosphorylating

41
Q

give an example of something phosphorylated in start checkpoint and what is freed?

A

Retinoblastoma protein, which frees EF2 (a TF therefore next cell phase begins)

42
Q

what can misregulation of CDKs and cyclins lead to?

A

uncontrolled growth (i.e. cancer)

43
Q

How does a separate complex (not associated to a particular checkpoint) but found in s phase initiate dna synthesis?

A

CDK+S cyclin initiates DNA synthesis by phosphorylating

44
Q

what can cdk and s cyclin complex phosphorylate to initiate dna synthesis? what does this stabilise?

A

Histone mRNA stem-loop binding protein, this stabilises histone mRNA

45
Q

what is phosphorylated in G2/M checkpoint? (3)

A

Nuclear lamins => break down nucleus
Myosin => prevents cytokinesis
Condensin => condenses chromosomes

46
Q

what complex is associated with checkpoint in G1(start)?

A

CDK+G1 cyclin & CDK+G1/S cyclin

47
Q

what destruction is associated with checkpoint (M) ?

A

destruction of M cyclin by APC

48
Q

what does apc do?

A

marks target cell cycle proteins for degradation

49
Q

true or false: CDK are active without cyclins

A

false they are inactivated without

50
Q

what is CAK?

A

CDK activating kinase

51
Q

what is Wee1?

A

CDK inactivating kinase

52
Q

how you activate cdk?

A

1) cyclin association

2) CAK is required

53
Q

what state is a CDK with cyclin but not CAK?

A

partly active

54
Q

what can reactivate a deactivated CDK/cyclin complex?

A

Cdc25 CDK activating phosphatase

55
Q

what does cdc25 CDK do?

A

reactivate an inactive cdk/cyclin complex

56
Q

what is does cyclin ubiquination do?

A

inactivates an active CDK/cyclin complex

57
Q

what is APC/c and what is it involved in?

A

anaphase promoting complex/cyclosome and it is involved in degradation of the cyclin and phosphate

58
Q

what does CAK add?

A

it is a kinase itself so adds a phosphate group

59
Q

why is the balance of synthesis/degradation important in terms of cyclins?

A

this balance is how they are regulated

60
Q

what is MAPK/K/K–> G1 cyclin expression?

A

a growth factor cascade

61
Q

what is needed to padd through a restriction point (start)?

A

sufficient activity

62
Q

what are p21 and p53?

A

CDK inhibitor proteins (CKIs)

63
Q

what are the two CDK inhibitor proteins?

A

p21 and p53

64
Q

what can DNA damage do in terms of p53?

A

can lead to phosphorylation and activation of p53 and thus expression of p21 (these are both CDK inhibitor proteins)

65
Q

if there is a mutation and dna is damaged p53 detects it,accumulates and the p21 is expressed which inhibits CDK, but what does this bind to and what does it do to this?

A

binds to s-cyclin and inactivates it,waits until dna damage is fixed and then p53 levels drop,as do p21 levels and the cell cycle continues

66
Q

what does damage to p53 and p21 lead to?

A

cancer (these are tumor suppressor genes)

67
Q

what are p53 and p21

A

tumor suppressor genes

68
Q

what is worse a single p53 or homozygous p53 mutation?

A

latter is far worse as no DNA damage will be detected

69
Q

what are oncogenes?

A

accelerators of cell cycle progression e.g TF

70
Q

what are tumour supressor genes?

A

inhibitors of cell cycle progression such as genes encoding p53 and RBP (retinoblastoma protein)

71
Q

what are 3 examples of oncogenes?

A

genes encoding Ras, RTKs, Myc

CBG Replication,transcription translation (10 decks)

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