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cell cycle - exam Flashcards

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1
Q

cell cycle

A
  • cycle of cell duplication and division
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2
Q

CELL CYCLE
two key tasks

A

1) Faithful DNA duplication
2) Accurate DNA segregation

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3
Q

Four phases of the eukaryotic cell cycle

A
  • G1 -> S -> G2 -> M
    G1: growth and preparation for DNA synthesis
    S: DNA replication
    G2: preparation for mitosis (organelle replication)
    M: mitosis + cytokinesis
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4
Q

Five stages of mitosis
defined on…

A

the basis of chromosome behaviour

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5
Q

Five stages of mitosis

A

1) prophase
2) prometaphase
3) metaphase
4) anaphase
5) telophase

cyctokinesis

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6
Q

Five stages of mitosis
1) prophase

A
  • Sister chromatid pairs disentangle and condense in the nucleus
  • nuclear envelope remains intact
  • Duplicated centrosomes (microtubule organising centre) move apart
  • Mitotic spindle assembles
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7
Q

Five stages of mitosis
2) Prometaphase:

A
  • Centrosome reaches the spindle pole
  • Breakdown of the nuclear envelope
  • Chromosomes attach to spindle microtubules via, kinetochore, and move
    o Kinetochore – the protein structure on chromatids where the spindle microtubules attach during cell division
  • The kinetochore attaches the chromosome to the spindle
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8
Q

Five stages of mitosis
3) Metaphase:

A
  • Centrosomes are at the spindle pole
  • Chromosomes are aligned at the spindle equator
  • A cell can pause in metaphase before it proceeds to the anaphase
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9
Q

Five stages of mitosis
4) Anaphase:

A
  • Sister chromatids synchronously separate
  • Daughter chromosomes move apart towards the spindle poles
  • Spindle poles more outward
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10
Q

Five stages of mitosis
5) Telophase

A
  • Two sets of daughter chromosomes arrive at the spindle poles and decondense
  • New nuclear envelopes assemble
  • contractile ring starts to contract
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11
Q

Five stages of mitosis
Cytokinesis:

A

: end of mitosis

completed nuclear envelope surrounds decondensing chromosomes

contractile ring creating cleavage furrow

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12
Q

the plant cell cycle

A
  • The cell plate is mase up of plasma membrane and cell wall components delivered in vesicles, and it partitions the cell in two
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13
Q

How do we study cell-cycle progression?

A

Morphological changes during cell-cycle progression

DNA features indicating cell-cycle progression

Cytoskeletal changes during cell-cycle progression

Live imaging of cell-cycle progression

Cellular markers indicating cell-cycle progression

Cell cycle analysis by quantitation of DNA content

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14
Q

How do we study cell-cycle progression?
Morphological changes during cell-cycle progression

A
  • Cell morphology/Appearance
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15
Q

How do we study cell-cycle progression?
DNA features indicating cell-cycle progression

A
  • DNA labelling: e.g. DNA-binding dyes
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16
Q

How do we study cell-cycle progression?
Cytoskeletal changes during cell-cycle progression

A
  • Mitotic spindle: e.g. antibodies recognising microtubules
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17
Q

How do we study cell-cycle progression?
Live imaging of cell-cycle progression

A
  • Time lapses
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18
Q

How do we study cell-cycle progression?
Cellular markers indicating cell-cycle progression

A
  • DNA synthesis e.g. artificial thymidine analogue BrdU (bromodeoxyuridine) is incorporated into newly synthesized DNA
  • Mitosis marker: e.g. anti-phospho-histone H3 (Ser10) antibody
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19
Q

How do we study cell-cycle progression?
Cell cycle analysis by quantitation of DNA content

A
  • DNA content: doubles during S phase, can be quantified by flow cytometry
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20
Q

BASICS OF CELL CYCLE
phases

A

o G1/S/G2/M

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21
Q

BASICS OF CELL CYCLE
- What defines the stages of mitosis

A

o Chromosome behaviour

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22
Q

BASICS OF CELL CYCLE
- How do we study cell-cycle progression

A

o Cell morphology
o DNA features
o Mitosis markers
o Flow cytometry

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23
Q

REGULATION OF CELL CYCLE

Study These Flashcards
A
  • Cycle of cell duplication and division
  • Cell cycle must be carefully controlled  must be able to stop if conditions change
24
Q

REGULATION OF CELL CYCLE
discovery of key regulators:
- Leland H. Hartwell

Study These Flashcards
A

o Discovered a specific class of genes, e.g. CDC28 (CDK), that control the cell cycle; introduced the concept “checkpoint”
o Checkpoint
 A stage in the eukaryotic cell cycle at which the cell examines internal and external cues and “decides” whether or not ot move forward with division

25
REGULATION OF CELL CYCLE discovery of key regulators: - Sir Paul M. Nurse
o Cloned and characterised CDK suggesting a general principle of cell cycle regulation
26
REGULATION OF CELL CYCLE discovery of key regulators: - Tim hunt
o Discovered the first cyclin
27
REGULATION OF CELL CYCLE Multiple cell cycle checkpoints
- The cell cycle is constantly checked (3 major checkpoints covered here) - The cell cycle control system triggers the major events of the cell cycle - Underlying molecular regulators: GAS vs BRAKE
28
REGULATION OF CELL CYCLE GAS:
cyclin-CDK complexes specific to cell cycle stages
29
REGULATION OF CELL CYCLE GAS: cyclin
: undergoes a cycle of synthesis and degradation – CDK regulator
30
REGULATION OF CELL CYCLE GAS: CDK
cyclin-dependent kinase, constantly present but inactive
31
REGULATION OF CELL CYCLE Cyclin-CDK complexes:
specific cell cycle stages e.g. cyclin d and Cdk4/6
32
REGULATION OF CELL CYCLE Activation of human CDK2
- Conformation change (t loop no longer blocks ATP binding site)
33
REGULATION OF CELL CYCLE Activation of human CDK2: role of proteins
- CDK: cyclin-dependent kinases -> modify their target proteins/drive cell cycle - Cyclin: CDK regulator -> undergo a cycle of synthesis and degradation - CAK: further activates the cyclin-CD complexes (changes morphology further)
34
REGULATION OF CELL CYCLE Multiple cell cycle checkpoints
3 major checkpoints
35
REGULATION OF CELL CYCLE Cell cycle checkpoints: G1/S or restriction (R) point
Transition from early to late G1 phase: restriction point - Restriction (R) point: start checkpoint or point of no return
36
REGULATION OF CELL CYCLE Cell cycle checkpoints: G1/S or restriction (R) point: combination of...
extrinsic and intrinsic signals
37
REGULATION OF CELL CYCLE Cell cycle checkpoints: G1/S or restriction (R) point: early G1
- Mitogen-dependent early G1: extrinsic growth-stimulating signals e.g. growth factors, CycD+CDK4/6
38
REGULATION OF CELL CYCLE Cell cycle checkpoints: G1/S or restriction (R) point: late G1
- Mitogen -independent late G1: intrinsic regulation, CycE+CDK2
39
REGULATION OF CELL CYCLE Cell cycle checkpoints: G1/S or restriction (R) point: pRB
- The retinoblastoma tumour suppressor protein (pRb or pRB) o Important protein that works un through the pathways
40
REGULATION OF CELL CYCLE Cell cycle checkpoints: G1/S or restriction (R) point: Rb/E2F pathway in cell cycle regulation
o Check integrity throughout G1 phase o Activation of E2F -> works with coactivators allows next stage of cell cycle to start
41
REGULATION OF CELL CYCLE Cell cycle checkpoints: G1/S or restriction (R) point: Rb/E2F pathway in cell cycle regulation: hyperphosphorylation...
inactivates Rb leading to activation of E2F
42
REGULATION OF CELL CYCLE G1/S or restriction (R) point - G1/S transition:
o DNA replication occurs in the S phase o DNA integrity needs to be checked before replication (intrinsic signals) o Mainly controlled by CDK2 o G1/S-cyclin: CycE o S-cyclin: CycA o The p53 pathway mediates DNA damage responses
43
REGULATION OF CELL CYCLE G1/S or restriction (R) point DNA break?
If DNA gets breaks it can be single stranded or double stranded If these breaks are detected cell cycle will be paused (allowing time for DNA to repair) If the damage is too bad to be repaired then the cell will die
44
REGULATION OF CELL CYCLE G1/S or restriction (R) point - The p53 pathway and G1/S checkpoint
Different stressors cause different breaks in DNA
45
Cell cycle checkpoints: G2/M - G2/M transition
o To assess DNA integrity (intrinsic signals) o Mainly controlled by CDK1 o M-cyclin: CycB o The p53 pathway again mediates DNA damage responses
46
P53 pathway in G1/S and G2/M checkpoints:
- ssDNA: generated by resection of DSBs - ChK: checkpoint kinase - CDC25a: phosphatase, to remove inhibitory phosphate for CDK - Wee1: kinase, to add inhibitory phosphate to CDK - GADD45: growth arrest and DNA damage-inducible gene - 14-3-3: kinase inhibitor
47
Cell cycle checkpoints: metaphase/anaphase spindle assembly checkpoint
o To ensure each chromosome is properly attached to the spindle apparatus and accurate DNA segregation
48
Cell cycle checkpoints: metaphase/anaphase APC/C
o A member of the ubiquitin ligase family of enzymes, multifunctional o To degrade S- and M-cyclins (CycA and B) (in order to move onto next stage) o Not all CDKs are degraded o To degrade securing allowing activation of separase to separate sister chromatids
49
APC/C regulates...
other phases of cell cycle - Substrate specificity and co-factors determine the outcome  SAC: spindle assembly checkpoint (metaphase/anaphase)  CDH1: CDC20 homologue-1 - Promotes cell cycle progression
50
Metaphase to anaphase transition (spindle assembly complex)
- Unattached kinetochores catalyse formation of the MCC (mitotic checkpoint complex) - MCC: composed of BubR1, Bub3, Mad2 and CDC20 - MCC inhibits APC/C (to pause/stop cell cycle)
51
BRAKE: ways to slow down or withdraw from the cell cycle
- CDK inhibitor proteins (CKIs): o Bind to cyclin-CDK complexes, e.g. p21 - Inhibit CDKs by modifying their phosphorylation sites o E.g. kinases and phosphatases - Formation of MCC to inhibit APC/C
52
Homeostasis tissue homeostasis
o Maintenance of the dynamic balance between cell proliferation, differentiation and death to preserve normal tissue morphology and function balance of cell proliferation, cell death and cell differentiation
53
Defective tissue homeostasis:
cancer
54
Cell cycle dysregulation and cancer oncogenes
the lack of inhibition or gain of function of which will lead to cancer cyclins CDKs E2F MYC Mdm2
55
Cell cycle dysregulation and cancer tumour supressors
the increased inhibition or loss of function of which will lead to cancer RB p53 p12, p27, p57 BRCA1, BRCA2

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