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Cell Cycle Regulation and Cancer Complete Summary
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Content covered in the cell cycle and regulation as well as cancer module of MCB2023S
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Cell Cycle RegulationLecture 1
Cell cycle = 24 hours (typical somatic animal cell)
Basic requirements of the cell cycle:
1. DNA must be accurately replicated
2. Replicated DNA must be segregated into two identical daughter cells
3. Cells must double their mass and duplicate cytoplasmic organielles in each
cell cycle
Traditional cell cycle study methods
- Light microscopy (used to study mitotic stage)
- Measuring DNA replication (S-phase)
o ddNTPs
o artificial thymidine (3-H thymidine) analog bromo-deoxyuridine (BrdU)
§ BrdU is incorporated opposite adenine during DNA replication
• Can be detected by probing cells with fluorescent tagged
antibodies that recognize BrdU
§ generation of antibodies via insertion of BrdU into organisms will
produce antibodies whose presence can be detected by
secondary antibody from a different organism
§ immunocytochemistry
§ BrdU would only be incorporated in replicating cells
o autoradiography to pick up 3H-thymidine incorporation (old method)
- check entry intro mitosis using nuclear envelope breakdown
Model systems for cell cycle study
Cell cycle = universal across all organisms
- Mammalian cell lines proliferating in culture
- Animal embryos
o xenoupus + sea urchin eggs
o genetic analysis in budding yeast and fission yeast
§ fission yeast divide via binary fission (mimics mammalian
example)
,Phases of the Cell Cycle
M
G2 phase
(3-4hr)
G0 phase
Quiesescent state
S phase (6-8hr) G1 phase
(DNA replication) (6-12hr)
Interphase = G1 + S + G2
à DNA is diffusely distributed within nucleus
S phase = DNA replication
G2 = second gap for growth and protein accumulation
M phase = chromosomal segregation and cell division
G1 = first gap, cell growth and preparation
*G0 = cell cycle arrest
Different types of cell cycles
• Embryonic
o Short cycles of constant duration
o Very synchronous rapid divisions in first 2 hours of cell division
o No G1 and G2 (cells are smaller than each parent cell)
o Replicate and divide, replicate and divide
• Growing (somatic mammalian cells)
o Longer cycles of variable duration
o Cells stay a constant size
o Long G1 and G2 phases allowing for growth and nutrient accumulation
• Reversible exit (eg. Neuron)
o Some cells stop growing and leave the cycle for a long period
,*can follow microtubule movement using Tau-GFP labelling
Cell Cycle In Multicellular organisms
- Controlled by growth factors (can allow a cell that has had reversible exit to
re-enter cell cycle for differentiation
o Fgf2 (causes neural stem cells to divide)
o TGFB (causes neural stem cells to stop dividing and differentiate into a
neuron instead)
Checkpoints
1. Mitotic control point (before mitosis) (G2/M transition)
a. Has the mass of the cell doubled
i. Would result in increasingly smaller cells if this was not true
b. DNA replication has completed
i. Same DNA must enter each daughter cell
c. DNA not damaged
i. Want whole complete chromosomes
ii. Don’t want to introduce mutations into daughter cells
2. Exit from mitosis control point (after mitosis)
a. Complete cell division
b. Have the chromosomes aligned correctly
c. Are all chromosomes attached to spindle
3. Start/Restriction Point (before DNA replication) (G1/S transition)
a. Check nutritional status
b. Check DNA is not damaged
, First Evidence of Regulators In Cell Cycle
- HeLa cells
o Cells cultured from biopsy of Henrietta Lacks suffering from cervical
cancer à continued to divide in culture
Dominant M phase factor
- Experiment:
o Artificially synchronize HeLa cells (somatic cells are asynchronous) with
a chemical agent causing fusion of membranes to form hybrid cells
o Fuse cells in different stages of mitosis
§ G1 + M à DNA in G1 cell immediately began to condense
(feature of mitosis)
• A dominant factor is present during mitosis that causes
the G1 cells to transition into a mitotic behavior regardless
of where it is in its own cell cycle
§ S + M à condensation of DNA occurs
§ G2 + M à condensation of DNA occurs
- Result: there is a dominant diffusible factor present during mitosis that can
cause mitotic induction in cells in other parts of cell cycle
Dominant S phase factor
- Experiment: synchronize cells in and mix populations
o G1 + S à G1 cells began to replicate DNA
- Result: Factors are present in S phase that can induce DNA replication in
another cell’s nucleus regardless of passing the Start checkpoint (G1 and S
fusion)
Block to DNA Re-Replication
- G2 + S à G2 nuclei do not induce another round of replication
§ Hybrid cells delay mitosis until S phase nucleus has completed
DNA replication
§ No new DNA synthesis in G2; delayed mitosis
- Result: there is a block to DNA re-replication (seen in G2 + S fusion)
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