The cell cycle, well detaild explenation, that include diagrams and and visual elements that will help you to undestands fully how it works, it is formed, and all topic related.
Week 12 MTC Notes
The Cell Cycle & Its Regulation
Ie. Cell Division/Reproduction
The Cell Cycle:
- The cell doctrine: “where a cell arises there must be a previous cell.”
- For a cell to reproduce, it must duplicate its contents & divide cyclically. (the cell cycle)
Fundamental tasks of the cell cycle:
• Copy and pass on genetic info to next generation.
• Produce 2 genetically identical daughter cells
• DNA in each chromosome must be accurately replicated
• Replicated chromosomes must be equally distributed between daughter cells.
• Coordinate growth with division to maintain size & contents.
4 Phases:
Ø Interphase
- Cell continues to transcribe genes, synthesize proteins, & grow.
1. G1 Phase (gap)
§ Provide additional time for cell to grow & duplicate
Cytoplasmic organelles
2. S Phase (synthesis)
§ DNA Replication
§ Restriction/Commitment Point – no turning back.
3. G2 Phase (gap)
§ Provide additional time for cell to grow & duplicate
Cytoplasmic organelles
§ Replicated chromosomes condense
Ø Mitosis & Cytokinesis
4. M Phase (mitosis & cytokinesis)
§ Prophase – nuclear membrane breaks down
§ Prometaphase – replicated chromosomes are lined up
§ Metaphase – chromosomes separated into 2 sister chromatids
§ Anaphase – chromatids arrive at ends of cell, decondense & form separate nuclear
membranes
§ Telophase – Plasma membrane pinches cell into 2.
5. G0 = Some cells (neurons) that don’t divide, just stop at G0.
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, The Cell-Cycle Control System:
- To ensure these tasks are completed, there exists a complex network of regulatory proteins, known
as the cell-cycle control system.
o Ordered series of biochemical switches that control the main events of the cycle:
§ DNA replication
§ Segregation of duplicated chromosomes
o Responds to various signals from outside & inside the cell
o Critical to regulation of cell numbers
o Malfunction can lead to cancer. (Abnormal number of chromosomes/Mutated DNA)
- Can stop the cycle using molecular ‘brakes’ at 2 important checkpoints.
Molecular Brakes of the Cell-Cycle Control System:
• Govern cell-cycle by activating & inactivating proteins that regulate DNA replication, mitosis &
cytokinesis.
• Activation via phosphorylation à by protein kinases (consume ATP + phosphorylate substrate)
• Deactivation via dephosphorylation à by protein phosphatases
• To become fully active, protein kinases must first become partially active by binding to a cyclin
• Cyclins – have no enzymatic activity.
• Cyclin Dependant Kinases (Cdk’s) – partly activated by cyclin.
o Cyclin + Cyclin Dependant Kinase = Cyclin-Cdk
• Cdk-Activating kinase (CAK) – phosphorylates the partly activated cyclin-Cdk, fully activating it.
o Activation of Cyclin-Cdk complexes can trigger cell-cycle events. (Entry into S-phase or M-
phase.)
§ ‘M’-Cyclin + Cdk = M-Cdk à drives cells into M-phase
§ ‘S’-Cyclin + Cdk = S-Cdk à drives cells into S-phase
Cdk Inactivation: Once ‘?’-Phase is complete, ubiquitin-dependant proteolysis destroys cyclins.
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