Overview
This lecture covers how the cell cycle regulates cell division, its importance for growth and cancer prevention, and the roles of key proteins and checkpoints.
Levels of Biological Organization
- All living organisms are made of one or more cells.
- In multicellular organisms, cells form tissues, which form organs, which work together in organ systems.
- Cells are specialized (e.g., skin, stomach, muscle cells) to perform different functions.
The Cell Cycle and Cell Division
- The cell cycle regulates when cells grow and divide.
- Organisms grow by cells dividing (mitosis), not by cells merely getting bigger.
- Cytokinesis is the splitting of the cytoplasm that follows mitosis.
- Most of a cell’s life is spent in interphase, not dividing.
Cancer and Uncontrolled Cell Division
- Cancer results from cells dividing uncontrollably due to failed regulation.
- Cancer cells may not communicate, function, or anchor themselves properly.
- Some cancers have genetic links; others are triggered by toxins, radiation, or UV exposure.
- Tumors are formed from uncontrolled cell growth; some stay localized, others spread.
Phases of the Cell Cycle
- Interphase: includes G1 (cell grows), S (DNA replicates), and G2 (cell grows and prepares for mitosis).
- M phase: includes mitosis and cytokinesis, where actual cell division happens.
- Most cells divide infrequently; certain cells like hair follicles divide more often.
Cell Cycle Checkpoints
- G1 checkpoint: checks for cell growth, DNA damage, and resources before DNA replication.
- G2 checkpoint: checks for correct DNA replication and adequate resources before mitosis.
- M (metaphase) checkpoint: ensures chromosomes are properly attached and aligned before separation.
Regulation and Apoptosis
- If checkpoint requirements are not met, cells pause for repairs or undergo apoptosis ("cell suicide") if damage cannot be fixed.
- Proteins regulate the cell cycle: positive regulators (allow progression, e.g., cyclin and Cdk) and negative regulators (stop cycle, e.g., p53).
- Cyclin levels fluctuate throughout the cycle, binding with CdK to regulate phase transitions.
G0 Phase: Non-dividing Cells
- Some cells enter G0, a resting phase where they do not prepare to divide but continue normal functions.
- Some cells (e.g., many neurons) may remain in G0 permanently and cannot divide.
Key Terms & Definitions
- Cell cycle — the sequence of growth and division in a cell.
- Mitosis — process of dividing the nucleus and genetic material.
- Cytokinesis — division of the cytoplasm after mitosis.
- Interphase — the phase in which the cell grows and DNA is replicated.
- G0 phase — resting phase for non-dividing cells.
- Checkpoint — control point where cell cycle progress is assessed.
- Apoptosis — programmed cell death for unrepairable cells.
- Cyclin — regulatory proteins controlling cell cycle progression.
- CdK (Cyclin-dependent kinase) — enzyme activated by cyclin to advance the cell cycle.
- p53 — protein that helps regulate apoptosis and cell cycle arrest.
Action Items / Next Steps
- Review cell cycle diagrams and phases (G1, S, G2, M, and G0).
- Learn the roles of cyclin, CdK, and p53 in cell cycle regulation.
- Prepare examples of how cancer relates to cell cycle dysregulation.