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CBG PANT Replication, transcription and translation > CBG Lecture 9: Cell Cycle > Flashcards

CBG Lecture 9: Cell Cycle Flashcards

1
Q

what is the cell cycle

A

a four phase internal clock in the cell that regulates cell division

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2
Q

which domain is it found in

A

eukaryotes

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3
Q

what are the four phases of the cell cycle

A 
INTERPHASE:
G1 - growth
S: Synthesis
G2: growth and prep for division
MITOSIS/MEIOSIS + CYTOKINESIS
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4
Q

what stages does interphase include

A

growth G1
synthesis
growth and prep for division G2

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5
Q

how long does G1 phase last

A

8 hours

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6
Q

how long does synthesis phase last?

A

DNA replication lasts c.12 hours

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7
Q

what happens ni synthesis phase

A

dna replication

eg. diploid to tetraploid

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8
Q

which phase is the longest in the cell cycle

A

synthesis: c.12 hours

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9
Q

what happens in G2 phase

A

growth and prep for cell division c. four hours

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10
Q

what happens in M phase

A

meiosis/mitosis/cytokinesis

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11
Q

how long does M phase last

A

half hour

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12
Q

what evidence exists for M phase

A

its histologically obvious - chromosomes condense

can see stages of meiosis and mitosis

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13
Q

what evidence is there for S phase

A

identify by 3H- thymidine autoradiography

50% of cells normally labelled, shows cells spend 50^ of their time in S phase

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14
Q

how can G1 and G2 phases be identified

A

use flourescent dyes to measure [DNA]

use flow cytometry

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15
Q

what is flow cytometry

A

each drip from vibrating nosel adds just a single cell, so if you add a flourescent dye, can tell which phase youre in by amount of flourescence

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16
Q

what is flow cytometry used for

A

measures [DNA] can see which phase of cycle a cell is in

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17
Q

which colour flourescence do cells in G2 phase show in flow cytometry

A

green

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18
Q

compare the amount of flourescence in G1 cells to G2

A

G2 has double amount of DNA than G1 therefore will have double the flourescence

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19
Q

which cells are used for fusion experiments

A

HeLa cells

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20
Q

what are HeLa cells

A

cervical cancer cells - immortal cells

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21
Q

what was the main result from fusion experiments

A

S phase nuclei induce S phase in G1 but not in G2

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22
Q

what is the result of a fusion experiment with a cell in S phase and a cell in G1 phase?

A

S contains factors that drive G1 to replicate DNA so get 2 S phase cells

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23
Q

what is the result of a fusion experiment with a cell in S phase and a cell in G2 phase?

A

G2 are refractory to the S phase factors, so no change to cells

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24
Q

what is the result of a fusion experiment with a cell in G2 phase and a cell in G1 phase?

A

no change

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25
Q

what did injection studies in frog oocytes show

A

maturation promoting factor can induce M phase in G2 nuclei

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26
Q

what does maturation promoting factor do

A

induce M phase in G2 nuclei

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27
Q

if you have a G2 cell and place in external control progesterone into it, what happens

A

induces M phase

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28
Q

how can M phase be induced

A

by adding progesterone

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29
Q

what does microinjection of M phase cytoplasm into G2 cells do

A

induces M phase

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30
Q

what can cell division cycle mutants do

A

help to understand cell cycle regulation

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31
Q

what are checkpoints in a cell cycle

A

restricition point in mammalian cell/start point in yeast where Cdc21/ Cdk1 all work

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32
Q

what happens to the cell cycle of yeast mutants

A

temperature sensitive yeast mutants arrect in G1 at high T

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33
Q

what is human homologue of Cdc28

A

Cdk1

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34
Q

what phase do temperature sensitive yeast mutants go to at high temperatures

A

G1 go to G0 at high temperatures

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35
Q

what are CDC mutants? what does CDC stand for

A

cell division cycle mutants Cdc28

36
Q

what does Cdk stand for

what can an arrest to Cdk1 do

A

cyclin dependent kinase

Cdk1 can cause arrest to G1 phase

37
Q

what are check points in a cell cycle regulated by

A

internal and external factors

38
Q

how many check points in the cell cycle are there

what are they

A

3
G1
G2/M
Metaphase

39
Q

what internal/external growth factors taken into account at G1 checkpoint

A

internal growth factors: cell size

external growth factors: growth hormones, hormone factors, check whether DNA is damaged

40
Q

what internal/external growth factors taken into account at G2/M checkpoint

A

internal: check all DNA present (can arrest at this point+wait/grow DNA)
is all DNA replicated
cell size
dna damage

41
Q

what internal/external growth factors taken into account at metaphase checkpoint

A

chromosome alignment

42
Q

how do you rectify misaligned chromosomes in metaphase checkpoint

A

use tubulin cytoskeleton

43
Q

what are cyclins

A

proteins that cycle in concentration over the cell cycle

44
Q

give an example of an S-type cyclin

A

cyclin D - which cycles in sea urchin embryos

45
Q

how does [S-type cyclin] change over time

A

levels build up from G1 through to S through to G2 and drop dramatically at G2/M checkpoint

46
Q

what is progress through the cell cycle controlled by

A

a cyclin dependent kinase

47
Q

whatt do cyclins do

A

detrermine the specificity of the CDK for its protein targets

48
Q

how many CDKs do yeast have, what?

A

yeast have a single CDK, vertebrates have several

49
Q

what can misregulation of CDKs result in

A

uncontrolled growth - cancer

50
Q

what are CDKs given specificity by

A

cyclins

51
Q

why wont CDKs work alone

A

cyclins tell CDKs what they should be modifying and which proteins they should switch on/off
enzymes to activate etc

52
Q

what is the passage through metaphase checkpoint associated with

A

the destruction of M cyclin by APC: anaphase promoting complex

53
Q

what is APC - what does it do

A

anaphase promoting complex

associated with the destruction of M cyclin

54
Q

what complex promotes passage through start/G1 checkpoints

A

CDK+ G1 cyclin

and CDK+G1/S cyclin

55
Q

how does first complex promote passage through start/G1 checkpoints

A

CDK+ G1 cyclin
and CDK+G1/S cyclin
oassage through start by phosphorylating
eg. Retinoblastoma protein which frees EF2 - transcription factor

56
Q

give an example of passage through start checkpoint of cell cycle

A

CDK + G1/S cyclin

retinoblastoma protein which frees EF2

57
Q

how do CDKs become activated

A

association with a cyclin makes it partly active

phosphorylation by CAK makes it fully active

58
Q

how does a CDK become partial active

A

association with cyclin

59
Q

how does a CDK become fully active

A

after association with cyclin, becomes phosphorylated by Cak

60
Q

how can CDK be both inactivated AND activated by phosphorylation

A

has multiple phosphorylation binding sites

61
Q

how is CDK inactivated

A

phosphorylation of 2 phosphate groups by Wee1

62
Q

How does CDK+S cyclin complex initiate synthesis

A

phosphorylation

63
Q

give an example of CDK+S cyclin complex initiating synthesis

A

histone mRNA stem-loop binding protein-stabilises histone mRNA

64
Q

how is DNA synthesis initiated

A

by CDK+S cyclin being phosphorulated

65
Q

what promotes passage through G2/M checkpoint

A

by CDK+M cyclin (maturation promoting factor)

66
Q

what is MPF made of

A

maturation promoting factor

CDK+M cyclin

67
Q

how is passage through G2/M checkpoint promoted

A

MPF (CDK+MCyclin) phosphrylation
eg. nuclear lamins - break down nucleus
myosin - prevent cytokinesis
condensin = condenses chromosomes

68
Q

what happens when cyclin synthesis>degradation

A

cyclin accumulates and can force cyclin CDK complex to go throughcheckpoint

69
Q

how is a CDK/cyclin complex broken down

A

cyclin ubiquitination by APC -anaphase promoting complex - and degraded
cyclin degraded, CDK is recycled

70
Q

how are cyclins regulated

A

by a balance of synthesis and degradation

71
Q

what pathway is used to regulate cyclins

A

MAPKinase/K/K patheay which results in G1 cyclin expression

72
Q

which pathway results in G1 cyclin expression

A

MAPK/K/K Growth factor cascade

73
Q

what are CDK/cyclin complexes inhibited by

A

Cdk inhibitor proteins (CKIs) like p21

74
Q

what is a CKI

A

Cdk inhibitor protein

75
Q

name a CKI

A

p21

76
Q

what is p21

A

a CDK inhibitor protein

77
Q

how can a mutation be detected

A

p53 presence

78
Q

what can a mutation in p53 and p21 do

A

more likely to replicate damaged/mutated DNA -> lead to cancer

79
Q

name some tumour suppressor genes

A

p21

p53

80
Q

what is a tumour suppressor gene

A

gene that encode proteins that act as brakes on cell cycle

81
Q

what type of mutation does a tumour supressor gene need to become dangerous

A

recessive mutation - both copies need to be broken

82
Q

give ecamples of tumour supressor genes

A

genes encoding p53

retinoblastoma protein

83
Q

what is an oncogene

A

gene that if a dominant mutation exists, it will accelerate cell cycle progression

84
Q

give ecample of oncogene

A

genes encoding Ras, RTKs,Myc

85
Q

how is an oncogene mutation dangerous

A

it generates the genes to be constituently on regardless of promoters/operatiors/repressors

CBG PANT Replication, transcription and translation (10 decks)

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