Mechanisms of Disease I - Cell Growth and Differentiation Flashcards
Define cell growth and differentiation
Cell growth - bigger organism, more cells
Differentiation - cells become complex, an end to growth
Cell growth precedes differentiation, but with some overlap
What are the 2 forms of cell growth
Hypertrophy - Bigger cells
Hyperplasia - more cells
Define Hypertrophy
Hypertrophy is simply cells growing bigger
More proteins, more membrane
Elevated protein synthesis is a big driver of increased cell size
Define Hyperplasia
More cells, caused by cell division or proliferation
Define differentiation
Where a cell exits the cell cycle and the cell is programmed to express type-specific genes.
Cell morphology and function changes
What is common between growth and differentiation
Cell growth and differentiation are governed by the integration of multiple signals: intra- and extracellular signals
Signals converge on the promoters of key genes
Promoters act as “co-incidence detectors”
Express gene YES/NO? How much?
What are the three types of ligand signalling methods
- Paracrine: produced locally to stimulate proliferation of a different cell type that has the appropriate cell surface receptor
- Autocrine: produced by a cell that also expresses the appropriate cell surface receptor
- Endocrine: like conventional hormones, released systemically for distant effects
What are the extracellular signals and what do they do ?
Stimulate proliferation and promote survival
Mitogens
e.g. Growth factors and interleukins (EGF, FGF, NGF, PDGF, IGF1, IL2, IL4)
Induce differentiation and inhibit proliferation, e.g. TGFb
Can do either, e.g. Wnt ligands
Induce apoptosis, e.g. TNFα and other members of the TNF family
Describe the growth factor signalling pathway in the cell
1) Growth factor binds receptor
2) Signal transducers activate kinase cascade
3) Transcription factors are activated in the nucleus
4) mRNA is translated into proteins
5) Proteins made can either return to there nucleus, remain in the cytoplasm or go the the cell membrane
Describe the phases of the cell cycle
G0 - Quiescent cells, Can either go onto becoming differentiated or rejoin the cell cycle
G1 - Cells grows in size as most macromolecules are synthesised
S - DNA replication occurs
G2 - The cell grows more
Mitosis - The cells divides into 2 daughter cells
How can we measure DNA content of a cell
Fluorescent flo cytometry
Describe how a flow cytometry table would look for Low rate of division
60% of cells would be in G1 where they have the lowest amount of DNA
20% of cells would be in S phase where there is slowly and increasing amount of DNA
20% would be in G2 where all the cells would have undergone DNA replication
Describe how a flow cytometry table would look for High rate of division
40% of cells would be in G1 where they have the lowest amount of DNA
40% of cells would be in S phase where there is slowly and increasing amount of DNA
20% would be in G2 where all the cells would have undergone DNA replication
In fluorescence microscopy what does each stain colour show
Blue= DNA
Red = γ-tubulin
Green = CHEK2
Yellow = centrioles
(γ-tubulin and CHEK2 colocalised)
Outline the checkpoints present in the cell cycle and what it checks for
1st check near end of G1, Check for DNA damage, cell size and metabolite/nutrient stores
2nd check at end of G2, Check for DNA damage and if DNA is completely replicated
3rd check during mitosis, Check for if chromosomes are aligned on spindle
Explain how Cyclin-dependant Kinases operate
When enough cyclin is present in the cell it binds and activates cyclin dependant kinases, which phosphorylates specific substrates
Cyclin is produced by the induction of Growth Factors
How is Cyclin-CDK activity regulated
Cycles of synthesis (gene expression) and destruction (by proteasome)
Post translational modification by phosphorylation
Dephosphorylation
Binding of cyclin-dependent kinase inhibitors (CDKIs)
Explain how Retinoblastoma is a key substrate for S-Phase initiation
Unphosphorylated RB binds E2F transcription factor preventing its stimulation of S-phase protein expression
Cyclin D-CDK4 and E-CDK2 phosphate RB and releases E2F
Released E2F stimulates the expression of more Cyclin E and
S-phase proteins
What happens when there’s DNA damage during the cell cycle
1) Stop the cycle
(cyclin dependent kinase inhibitors, CHEK2 etc.)
2)Attempt DNA repair
(nucleotide or base excision enzymes, mismatch repair etc.)
3) if repair impossible
Programmed Cell Death (BCL2 family, caspases)
What is the role of Tumour protein 53
TP53 is normally destroyed by proteasome in a normal cells,
When there is DNA damage kinase activation phosphorylates TP53 so it isn’t destroyed.
phosphorylated TP53 can cause:
1) DNA Repair
2) Apoptosis
3) Expression of CDKI, cell cycle arrest
What would the effects be of the loss of TP53
TP53 loss-of-function mutations are amongst the most frequent in cancer
- Prevent cell cycle arrest
- Prevent apoptosis
- Prevent DNA repair
How does S-phase chemotherapy drugs work
Objective: stop proliferation, induce apoptosis
S-phase drugs cause DNA damage, e.g.
5-fluorouracil (prevents synthesis of thymidine)
Cisplatin (binds to DNA causing damage and blocking repair)
How does M-phase chemotherapy drugs work
M-Phase drugs target the mitotic spindle
Vinca alkaloids:
stabilize free tubulin
prevent microtubule polymerization
arrest cells in mitosis
Paclitaxel (Taxol):
stabilizes microtubules
preventing de-polymerization
arrests cell in mitosis
