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Molecular Biology of the Cell > Section 4 Lecture 1 Cell Cycle & Control > Flashcards

Section 4 Lecture 1 Cell Cycle & Control Flashcards

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1
Q

What are the checkpoints that regulate the cell cycle?

A 
G1/S = START Transition
S/G2 = ATR blocks CDK1
G2/M = Is all DNA replicated?
Metaphase-to-Anaphase = Are all the chromosomes attached to the spindle and aligned at the equator?
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2
Q

CDKs can function without binding to the cyclins. T/F

A

False

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3
Q

Yeast have only one Cdk. T/F

A

True. CDK1

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4
Q

Between the S and the M phase, which is shorter?

A

M Phase

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5
Q

Interphase includes which phases?

A

G1
S
G2

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6
Q

How do early embryonic cell cycles differ from normal cell cycles?

A

Lack G1 and G2 gap phases

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7
Q

Cell Cycle commitment occurs in the M phase of the cell cycle. T/F

A

False. G1 Phase

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8
Q

In what phase do most of the cells in our body exist in?

A

G0

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9
Q

Metaphase to anaphase transition is controlled by phosphorylation events. T/F

A

False. APC/C activity ubiquinates/ degrades M-cyclins, S-cyclins and securin.

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10
Q

Which activity is constant vs. varies throughout the cell cycle?
APC/C activity
SCF activity

A

APC/C changes

SCF constant

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11
Q

During what cell cycles does cell growth occur?

A

All active phases except mitosis

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12
Q

What cell type does Meiosis and Mitosis act on?

A 
Meiosis = Germ line 
Mitosis = Somatic
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13
Q 
MITOSIS vs MEIOSIS
# of cell divisions
# of daughter cells
Type of daughter cells
Genetically \_\_\_\_\_\_\_
Cell type specificity
A 
MITOSIS vs. MEIOSIS
1 vs. 2
2 vs. 4
Diploid vs Haploid
Identical vs. Different
Somatic vs Germ line
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14
Q

In what phase does nuclear envelope breakdown occur?

A

M phase, Prophase

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15
Q

In what phase does DNA synthesis occur?

A

S phase

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16
Q

In what phase do sister chromatids align at the equator?

A

M phase, Metaphase

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17
Q

In what phase do sister chromatids attach to the spindle?

A

M phase, Prometaphase

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18
Q

In what phase do sister chromatids begin separating?

A

M phase, Anaphase

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19
Q

In what phase does the spindle disassemble?

A

M phase, Telophase

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20
Q

In what phase do the chromosomes segregate into separate nuclei?

A

M phase, Telophase

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21
Q

In what phase do DNA molecules condense into sister chromatids?

A

M phase, Prophase

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22
Q

What does securin do?

A

linkages that hold duplicated chromosomes

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23
Q

What are the 3 features of cell cycle checkpoints?

A
  1. Binary
  2. Robust
  3. Adaptable
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24
Q

Cdk

A

Cyclin-dependent protein kinases

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25
Q

Which is constant vs. varies throughout the cell cycle?
Cdks
Cyclins

A 
Cdks = Constant
Cyclins = Varies
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26
Q

CAK

A

Cdk - Activating Kinase

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27
Q

How do cyclins activate Cdks?

A

T-Loop blocks activation site normally on Cdk. When cyclin binds, T-loop moves out, exposing the activation site (partially activated). CAK can then phosphorylates the T-loop (fully activated).

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28
Q

T-loop

A

Threonine residues on the Cdk that are phosphorylated after unblocking the Cdk active site.

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29
Q

3 ways of regulating Cyclin-CDK activity

A
  1. Wee 1 Kinase/ Cdc 25 Phosphatase
  2. CKI proteins
  3. Ubiquitin Ligases Complexes
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30
Q

CKI

A

Cdk-inhibitory proteins

Deactivate cyclin-Cdk by creating CKI-cyclin-Cdk complex with 3 point contact mode of inhibition.

31
Q

Example of CKI

A

p27

32
Q

When does CKI act on?

A

CKI govern early cell cycle events

33
Q

What are 2 ubiquitin ligase complexes?

A

APC/C

SCF

34
Q

APC/C

A

Anaphase Promoting Complex or Cyclosome

35
Q

SCF

A

Skp, Cullin, F-Box containing protein complex

36
Q

APC/C targets?

A

Targets:
Securin
S cyclins
M cyclins

37
Q

When is APC/C activated and by what?

A

Mid-Mitosis by Cdc 20

Late mitosis to early G1 by Cdh1

38
Q

When is APC/C deactivated?

A

G1/S transition

39
Q

SCF targets?

A

CKIs and G1/S cyclins

40
Q

Why is APC/C important?

A

Allows for metaphase-to-anaphase transition to occur

41
Q

When is SCF activated?

A

Late G1 > CKIs

Early S phase > G1/S cyclins

42
Q

Why is SCF important?

A

Allow S phase to continue with active S-Cdk activity

43
Q

What do mitogens do?

A

Stimulate cell division

G1-Cdk and G1/S-Cdk activation via cyclins

44
Q

What are the 4 cyclins?

A

G1/S
S
M
G1

45
Q

What are the 4 checkpoints?

A

G1 (START)
S/G2
G2/M
Metaphase-to-Anaphase

46
Q

Growth Factors

A

Protein Synthesis (Ribosomes) to increase bulk of cell

47
Q

Survival Factors

A

Suppress apoptosis

48
Q

PDGF

A

Platelet-derived growth factor

1st mitogen to be identified

49
Q

TGFB

A

anti-mitogenic protein

50
Q

Rb

A

Retinoblastoma tumor suppressor
Mediates mitogen-driven cell cycle entry
Inactivates E2F transcription factor
Is inactivated by G1-Cdk

51
Q

E2F

A

Transcription factor
Inactivated by Rb
Mediates mitogen-driven cell cycle entry
Once activated, trascribes for S-phase gene > G1/S cyclin and S cyclin

52
Q

Steps of Mitogen-driven cell cycle entry mediated by Rb and E2F

A 
Mitogen binds to extracellular receptor
> Ras activation
> MAPK Cascade activation
> In nucleus, transcription activation of regulatory proteins
 =>Immediate early gene expression 
>Myc upregulation 
=>Delayed-response gene expression 
> Myc upregulates G1 cyclins
>G1-Cdk activated
>G1-Cdk phosphorylates Rb = deactivates Rb
>E2F activated 
>S phase genes transcribed
>G1/S cyclin and S cyclin transcribed
>G1/S-Cdk and S-Cdk activated
>Positive feedback loop to E2F
>DNA Synthesis
53
Q

Myc

A

Transcription regulatory protein product of E2F/Rb Ras to MAP Kinase cascade/ immediate early gene expression
Transcriptionally upregulates G1 cyclins > Activates G1-Cdk and phosphorylates Rb

54
Q

How do abnormally high proliferation signals cause cell death/ cell arrest?

A

Abnormally high Myc > Arf expression > Arf inactivates Mdm2 > p53 active/ stable > cell arrest/ apoptosis

55
Q

Mdm2

A

Ubiquitin ligase that deactivates p53 and leads to its degradation in proteosomes

56
Q

DNA damage = Cell arrest

A

p53 activation

  1. DNA damage
  2. ATM/ATR kinase activated
  3. Chk1/Chk2 kinase activated
  4. p53 phosphorylated = active/ stable
  5. p53 binds to p21 gene regulatory region > transcription > translation
  6. p21 = CKI deactivates G1/S Cdk and S Cdk
57
Q

ATM/ATR kinase

A

p53 activation to cell arrest mechanism component triggered by DNA damage

58
Q

Chk1/Chk2 kinase

A

p53 activation to cell arrest mechanism component triggered by ATM/ATR kinase and leads to phosphorylation of p53

59
Q

Arf

A

product of abnormally high Myc

deactivates Mdm2

60
Q

3 cell grown and division types

A

A: Extracellular factor to cell growth to cell division only when growth reaches minimal threshold
B. Growth factor to cell growth separately from Mitogen to cell division. Controlled separately/ uncoupled.
C. Extracellular factor to cell growth and cell division.

61
Q

TOR pathway

A
  1. Growth factor binds RTKs > PI3K > PIP3 which acts as a binding site for TOR where it is activated leads to increased production of ribosomes (protein synthesis)
62
Q

TOR products

A
  1. Transcription of ribosome synthesis genes
  2. Activates S6K> activates S6 (ribosomal protein) > increased ability of ribosomes to translate ribosomal subunit mRNAs
  3. Inhibits 4E-BP (inhibitor of elF4E) > activates translation factor elF4E
    => Increased production of ribosomes
63
Q

What are 5 ways to study the cell cycle?

A
  1. Budding yeast
  2. Mammalian tissue samples
  3. Xenopus eggs and fly eggs
  4. BrdU labeling
  5. FACs (Flow Cytometry)
64
Q

What are the benefits to studying with budding yeast?

A 
reproduce rapidly
small genome 
easily altered or deleted - gene mutants with conditional in order to propogate
analysis by light microscopy
replicate in haploid cell
65
Q

What are the common budding yeast mutants?

A

TS (temperature sensitive) mutants
Conditional
Proteins fold in lower temperature but do not fold correctly at high temp

66
Q

2 examples of TS budding yeast mutants

A
  1. Halted at G1 phase since misfolded DNA cannot replicate in the S phase.
  2. Cdc 15 mutant yeast - Cdc 15 gene affects metaphase to anaphase transition. They complete anaphase but cannot exit from mitosis. Cell arrest with large buds.
67
Q

Advantages of studying with Xenopus and Drosophila embryos?

A

large size
can be microinjected
fertilization leads to series of rapid cell divisions without egg growth
No gap phase in early stages

68
Q

Benefits to studying with mammalian tissues

A

Immortalized cell lines
Visualize by microscopy
Cells can be stained with DNA-binding dyes and antibodies

69
Q

BrdU labeling

A

BrdU is a Thymidine analog

With α-BrdU antibodies, can visualize all new cells

70
Q

Flow Cytometry (FACs)

A

Uses fluorescent DNA binding dyes
Cells sorted according to their density of fluorescence (DNA content)
In S phase, DNA content doubles
Can follow a synchronized cell population over time to determine length cell cycle
x axis = DNA content/ density of fluorescence
y axis = # of cells
Shows that most cells are in G1 (G0) at any given time

71
Q

2 ways to sync cells

A
  1. Inhibition of DNA synthesis with chemicals
    i. e. hydroxyurea blocks at G1/S checkpoint > released into synced Cdc after 24 hours
  2. Nutritional Deprivation - no serum for 24 hours in culture medium > accumulates cells into G1 phase > release synced into Cdc by adding serum
72
Q

Cdc

A

Cell-division-cycle

73
Q

Examples of chemicals to inhibit DNA synthesis

A
  1. hydroxyurea (HU)
  2. thymidine
  3. aminopterin
  4. cytosine

Molecular Biology of the Cell (2 decks)

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