Cell cycle and it's checkpoints
- 2. • Cell division is very important process in a living organisms. During the division of a cell, DNA replication and cell growth also tales place. • All the processes, i.e., cell division, DNA replication, and cell growth, hence have to take place in a coordinated way to ensure correct division and formation of progeny cells containing intact genomes. • Although growth (in terms of cytoplasmic increase) is a continuous process, DNA synthesis occurs only during one specific stage in the cell cycle. • The replicated chromosomes (DNA) are then distributed to the daughter nuclei by a complex series of events during cell division. These events are themselves under genetic control. Complete life cycle is called as cell cycle.
- 3. There are 2 phases of cell cycle :- 1. Interphase 2. M-phase
- 5. The most active phase of the whole cell cycle. Constitutes 95% of whole cell cycle. It is the preparatory phase for cell division. In interphase metabolism of cell increases. A series of metabolic changes occurs during interphase in cell. These changes are not visible under microscope, so some scientists termed interphase as resting phase.
- 6. Howard and Pelc classifieds interphase into 3 subjects categories. 1. G1 phase or Pre DNA synthesis phase (1st gap phase) 2. S phase (DNA Synthesis phase) 3. G2 phase (2nd Gap phase) or Post DNA synthesis phase (Pre mitosis phase).
- 7. G1 phase also known as pre synthetic phase as it occurs between mitosis and initiation between DNA replication, During this stage cell is metabolically active and continuously grows. Cell organelle increase and rapidly synthesizes different types of RNA and proteins. As now proteins are available, so synthesis of new protoplasm takes place and start growing in size. Cell grows maximum in this phase.
- 8. Replication of nuclear DNA and synthesis of histone protein. The DNA amount becomes double. Note: Amount of DNA becomes double but Chromosome duplication do not takes place.
- 9. Occurs during this phase. Proteins are synthesized in Final preparation of M- Phase preparation for mitosis Example- formation of Tubulin Protein which is required for spindle fibres formation while cell growth continues.
- 10. 0 0.5 1 1.5 2 2.5 3 3.5 4 M PHASE G1 PHASE S PHASE G2 PHASE
- 11. IT HAS 4 PHASES : 1. •Prophase 2. •Metaphase 3. •Anaphase 4. •Telophase
- 12. •Centrioles which had undergone duplication during S-Phase start moving towards the opposite pole. •End of prophase do not show golgi apparatus, Endoplasmic nucleus and nuclear envelope.
- 13. •Best stage to study morphology of chromosome. •Disintegration of nuclear envelope
- 15. •Also known as reverse prophase. •Cytokinesis takes place which starts in late anaphase.
- 17. HOW THE CELL IS CONTROLLED? IS IT ONLY THIS MUCH? WITHOUT ANY PREPARATION HOW CAN IT BE DONE? PREPARATION FOR THIS IS ALSO NEDED. THIS ALL WILL BE TAUGHT TO YOU IN THE TOPIC CELL REGULATION , CHECK POINTS AND PROTIENS REQUIRED FOR THIS.
- 18. Leland and H. Hartwell, R. Timothy Hunt and Paul M. Nurse won the 2001 Nobel Prize in Physiology or Medicine for the discovery of the central molecules like cyclins and cyclin dependent kinase (CDKs). Nurse, T. Hunt and Hartwell in 2001 studied cell cycle in sachcharomyces (Baker yeast).
- 19. The cell cycle has major 3 check points 1. First check point- Late G1 check point 2. Second check point- Late S check point 3. Third check point- Metaphase or anaphase transition point Regulation in a cell cycle at check points occour using regulatory proteins such as CYCLIN, CYCLIN- Dependent kinase, ANAPHASE-Promoting complex, and many other proteins.
- 22. Phosphorylates the Threonine or Serine Residues of its target protein. Phosphorylated proteins in turn result in the initiation or regulation of major cell cycle events such as replication (S phase), mitosis, and cytokinesis (M phase). But the phosphrylation role of CdK is mediated by Cyclin. cyclin combines with Cdk forming an active cyclin- Cdk complex(CCC).CCC is functional only in
- 23. There are 3 types of Cyclin , depending on the phases of cell cycle at which they function: a) G1/S cyclin, which binds to the CdK at the end of the G1 and function in the S phase by promoting DNA Synthesis. b) S cyclin, which binds to the CdK in the Sphase and stimulates DNA replication c) M cyclin, which binds to CdK in the M phase and promotes mitosis.
- 24. Regulation includes:- 1.Activation of cyclin-CdK complex 2.Inhibition of cyclin-CdK complex
- 25. •The activity of CDK is regulated by the formation or dissociation of CCC. •The active site of CdK is a cleft blocked by a T-loop. •Binding of cyclin with CdK dislocates the loop and exposes the active site, forming CCC. •Phosphorylation of threonine residue induces changes in the loop and forms completely active CdK, capable of phosphorylating the proteins involved in the cell regulation. .
- 26. •CdK contains tyrosine residue at the roof of active site which is the site of inhibition . •An enzyme called wee 1 kinase phosphorylates the tyrosine, leading to the inactivation of
- 27. Done with the help of CAK CdK activating kinase . CAK dephosphorylates the roof of active site and reactivates the CCC.
- 29. In cancer cells check points do not work properly leading to uncontrolled division. The total heredity material which occur outside the chromosome is called plasmogene. Some cells in adult animals do not appear to exhibit division are heart cells The cells which do not divide in Go phase are neurons.
- 30. Thank you For any query or doubts mail me at- ritisha.gupta9719@gmail.com Ritisha Gupta