Section 4 Lecture 1 Cell Cycle & Control Flashcards
(73 cards)
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?
2
Q
CDKs can function without binding to the cyclins. T/F
A
False
3
Q
Yeast have only one Cdk. T/F
A
True. CDK1
4
Q
Between the S and the M phase, which is shorter?
A
M Phase
5
Q
Interphase includes which phases?
A
G1
S
G2
6
Q
How do early embryonic cell cycles differ from normal cell cycles?
A
Lack G1 and G2 gap phases
7
Q
Cell Cycle commitment occurs in the M phase of the cell cycle. T/F
A
False. G1 Phase
8
Q
In what phase do most of the cells in our body exist in?
A
G0
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.
10
Q
Which activity is constant vs. varies throughout the cell cycle?
APC/C activity
SCF activity
A
APC/C changes
SCF constant
11
Q
During what cell cycles does cell growth occur?
A
All active phases except mitosis
12
Q
What cell type does Meiosis and Mitosis act on?
A
Meiosis = Germ line Mitosis = Somatic
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
14
Q
In what phase does nuclear envelope breakdown occur?
A
M phase, Prophase
15
Q
In what phase does DNA synthesis occur?
A
S phase
16
Q
In what phase do sister chromatids align at the equator?
A
M phase, Metaphase
17
Q
In what phase do sister chromatids attach to the spindle?
A
M phase, Prometaphase
18
Q
In what phase do sister chromatids begin separating?
A
M phase, Anaphase
19
Q
In what phase does the spindle disassemble?
A
M phase, Telophase
20
Q
In what phase do the chromosomes segregate into separate nuclei?
A
M phase, Telophase
21
Q
In what phase do DNA molecules condense into sister chromatids?
A
M phase, Prophase
22
Q
What does securin do?
A
linkages that hold duplicated chromosomes
23
Q
What are the 3 features of cell cycle checkpoints?
A
- Binary
- Robust
- Adaptable
24
Q
Cdk
A
Cyclin-dependent protein kinases
25
Which is constant vs. varies throughout the cell cycle?
Cdks
Cyclins
```
Cdks = Constant
Cyclins = Varies
```
26
CAK
Cdk - Activating Kinase
27
How do cyclins activate Cdks?
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).
28
T-loop
Threonine residues on the Cdk that are phosphorylated after unblocking the Cdk active site.
29
3 ways of regulating Cyclin-CDK activity
1. Wee 1 Kinase/ Cdc 25 Phosphatase
2. CKI proteins
3. Ubiquitin Ligases Complexes
30
CKI
Cdk-inhibitory proteins
| Deactivate cyclin-Cdk by creating CKI-cyclin-Cdk complex with 3 point contact mode of inhibition.
31
Example of CKI
p27
32
When does CKI act on?
CKI govern early cell cycle events
33
What are 2 ubiquitin ligase complexes?
APC/C
| SCF
34
APC/C
Anaphase Promoting Complex or Cyclosome
35
SCF
Skp, Cullin, F-Box containing protein complex
36
APC/C targets?
Targets:
Securin
S cyclins
M cyclins
37
When is APC/C activated and by what?
Mid-Mitosis by Cdc 20
| Late mitosis to early G1 by Cdh1
38
When is APC/C deactivated?
G1/S transition
39
SCF targets?
CKIs and G1/S cyclins
40
Why is APC/C important?
Allows for metaphase-to-anaphase transition to occur
41
When is SCF activated?
Late G1 > CKIs
| Early S phase > G1/S cyclins
42
Why is SCF important?
Allow S phase to continue with active S-Cdk activity
43
What do mitogens do?
Stimulate cell division
| G1-Cdk and G1/S-Cdk activation via cyclins
44
What are the 4 cyclins?
G1/S
S
M
G1
45
What are the 4 checkpoints?
G1 (START)
S/G2
G2/M
Metaphase-to-Anaphase
46
Growth Factors
Protein Synthesis (Ribosomes) to increase bulk of cell
47
Survival Factors
Suppress apoptosis
48
PDGF
Platelet-derived growth factor
| 1st mitogen to be identified
49
TGFB
anti-mitogenic protein
50
Rb
Retinoblastoma tumor suppressor
Mediates mitogen-driven cell cycle entry
Inactivates E2F transcription factor
Is inactivated by G1-Cdk
51
E2F
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
Steps of Mitogen-driven cell cycle entry mediated by Rb and E2F
```
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
Myc
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
How do abnormally high proliferation signals cause cell death/ cell arrest?
Abnormally high Myc > Arf expression > Arf inactivates Mdm2 > p53 active/ stable > cell arrest/ apoptosis
55
Mdm2
Ubiquitin ligase that deactivates p53 and leads to its degradation in proteosomes
56
DNA damage = Cell arrest
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
ATM/ATR kinase
p53 activation to cell arrest mechanism component triggered by DNA damage
58
Chk1/Chk2 kinase
p53 activation to cell arrest mechanism component triggered by ATM/ATR kinase and leads to phosphorylation of p53
59
Arf
product of abnormally high Myc
| deactivates Mdm2
60
3 cell grown and division types
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
TOR pathway
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
TOR products
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
What are 5 ways to study the cell cycle?
1. Budding yeast
2. Mammalian tissue samples
3. Xenopus eggs and fly eggs
4. BrdU labeling
5. FACs (Flow Cytometry)
64
What are the benefits to studying with budding yeast?
```
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
What are the common budding yeast mutants?
TS (temperature sensitive) mutants
Conditional
Proteins fold in lower temperature but do not fold correctly at high temp
66
2 examples of TS budding yeast mutants
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
Advantages of studying with Xenopus and Drosophila embryos?
large size
can be microinjected
fertilization leads to series of rapid cell divisions without egg growth
No gap phase in early stages
68
Benefits to studying with mammalian tissues
Immortalized cell lines
Visualize by microscopy
Cells can be stained with DNA-binding dyes and antibodies
69
BrdU labeling
BrdU is a Thymidine analog
| With α-BrdU antibodies, can visualize all new cells
70
Flow Cytometry (FACs)
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
2 ways to sync cells
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
Cdc
Cell-division-cycle
73
Examples of chemicals to inhibit DNA synthesis
1. hydroxyurea (HU)
2. thymidine
3. aminopterin
4. cytosine
