Overview
This lecture explains the cell cycle, its phases, regulation mechanisms, the relationship to cancer, and introduces key cell cycle vocabulary and proteins.
Levels of Biological Organization
- Living things are made of one or more cells, as stated in the cell theory.
- Cells form tissues, tissues form organs, and organs form organ systems in multicellular organisms.
- Different cell types (skin, muscle, stomach) are specialized for specific functions.
Cell Growth and Division
- Multicellular organisms grow by producing more cells through cell division, not by enlarging individual cells.
- Mitosis, followed by cytokinesis, produces new body cells.
- Cell division must be regulated to prevent uncontrolled growth.
Cancer and Uncontrolled Cell Division
- Cancer results from cells dividing too frequently and losing regulatory control.
- Cancer cells may lack communication, normal functions, anchoring, and can divert nutrients from healthy cells.
- Risk factors include genetics, toxins, radiation, and excessive UV exposure.
- Uncontrolled cell division forms tumors, which may be stationary or spread.
The Cell Cycle and Its Phases
- The cell cycle is divided into interphase (cell growth, DNA replication, normal functions) and M phase (mitosis and cytokinesis).
- Most cells spend their time in interphase, not dividing.
- Phases of interphase include G1 (cell grows), S (DNA synthesis), and G2 (cell prepares for mitosis).
- M phase is when the cell actually divides.
Checkpoints & Regulation
- G1 checkpoint: checks cell growth, DNA damage, and available resources.
- G2 checkpoint: checks correct DNA replication and sustained growth.
- M (metaphase) checkpoint: ensures chromosomes are properly aligned and attached to the spindle.
- If a cell fails a checkpoint, it may pause to fix the issue or undergo apoptosis (self-destruction).
Regulatory Proteins
- Genes code for proteins that regulate the cell cycle, responding to internal and external cues.
- Cyclins and Cdks (cyclin-dependent kinases) are positive regulators, enabling progression through phases.
- Different cyclins bind Cdks in different phases; their concentration rises and falls based on signals.
- Negative regulators, like the p53 protein, can initiate apoptosis.
Special Cell Cycle Conditions (G0 Phase)
- Some cells enter G0 phase, a resting state where they do not prepare to divide but still function.
- Some cells remain in G0 temporarily; others, like many neurons, stay permanently and do not divide.
Key Terms & Definitions
- Cell Cycle — series of phases cells go through to grow and divide.
- Mitosis — process where the cell nucleus divides.
- Cytokinesis — division of the cytoplasm after mitosis.
- Interphase — phase where the cell grows and replicates DNA.
- G1 Phase — period of cell growth before DNA replication.
- S Phase — phase where DNA is synthesized (replicated).
- G2 Phase — further cell growth and preparation for mitosis.
- M Phase — mitosis and cytokinesis occur.
- Checkpoint — control point where conditions are assessed before proceeding.
- Apoptosis — programmed cell death.
- Cyclin/Cdk — proteins that regulate progression through the cell cycle.
- p53 — protein involved in triggering apoptosis.
- G0 Phase — resting phase where cells do not divide.
Action Items / Next Steps
- Review cell cycle phases and checkpoints.
- Explore more on cyclins, Cdks, and apoptosis-related proteins.
- Study differences between cancerous and healthy cell division processes.