Mechanisms of disease Flashcards
How can the cell cycle be visualised/quantified?
visualised via fluorescence microscopy which generates stains of proteins.
quantified via fluorescent flow cytometry which measures the DNA content of every cell population
How is the cell cycle regulated?
Regulated via cyclin-dependent kinases (CDK) which form a complex with cyclin, causing its activation. It then phosphorylates a specific substrate protein.
This is regulated by:
- continuous cycles of synthesis/apoptosis
- post-translational modification via phosph.
- dephosphorylation
- binding of CDKI
What are cyclins?
encoded by 20 genes, cyclins are regulatory subunits controlled by GF
What are CDKs?
encoded by 10 genes, CDKs are catalytic subunit
Explain the mechanism of retinoblastoma protein .
1/ unphosphorylated Rb binds to E2F transcription factors, preventing expression of S-phase proteins
2/ in presence of cyclin D-CDK4 or cyclin E-CKD2, Rb becomes phosphorylated and drives replication. It also stimulates expression of more cyclin E, creating a positive feedback.
Explain the regulation of cell cycle and apoptosis.
- GF drive early gene expression - TF FOS, JUN, MYC
- This stimulates delayed gene expression
- E2F sequestered by binding to unphosphorylated RB
- G1 cyclin-CDK complexes hypophosphorylate Rb allowing more E2F activity + more cyclin E, S-phase proteins
- G1/S phase cyclin-CDK complexes hyperphosphorylate Rb - stimulating release of E2F
Switches activated by post-translational modification or removal of inhibitors
Explain mechanisms by which growth control can be disrupted in neoplasia
TP53 is continually destroyed by proteasome.
Mutagen binding induce activation of protein kinases which phosphorylate TP53 preventing its destruction to:
- drive expression of CDK (malfx: cells proliferate faster)
- activates DNA repair mechanism (malfx: more mutations)
- induce apoptosis (malfx: become resistant to dying)
Define drugs acting on the cell cycle: S-phase drugs
they cause DNA damage
- 5-fluorouracil - prevent thymidine synthesis
- cisplatin - binds to DNA to cause damage and block repair
Define drugs acting on the cell cycle: M-phase drugs
they target the mitotic spindle: vinca alkaloids, paclitaxel : - stabilises microtubules - prevent polymerisation - arrest cells in mitosis
Define the response of the cell in response to DNA damage
may trigger cell cycle arrest or apoptosis:
- stop the cell cycle - CDKI genes, CHEK2, etc.
- DNA repair - nucleotide/base excision enzymes, mismatch repair, etc.
- programmed cell death - BLC family, caspases