Mitosis, Meiosis and Cell Cycle Regulation

  • Introduction to Mitosis and Meiosis

    • Mitosis: Cell division for somatic (non-reproductive) cells.
      • Produces two genetically identical daughter cells from a single parent cell.
    • Meiosis: Cell division for gametes (egg and sperm cells).
      • Produces four genetically different daughter cells, each with half the hereditary material of the parent cell.
      • Important for genetic diversity.

  • Cytokinesis

    • Refers to the division of the cytoplasm during cell division, resulting in two daughter cells.
    • Occurs after mitosis and meiosis.

  • Processes of Cell Replication

    • The basic steps for cell replication include:
      1. DNA Replication: All genetic material must be copied.
      2. Separation of Copies: The replicated DNA separates into two sets.
      3. Cytokinesis: The cytoplasm divides to form two cells.
    • Example: Stomach epithelial cells regularly replicate because their environment is harsh and they need constant replacement.

  • Cell Cycle Phases

    • Interphase (most of the cell's life):
      • G1 Phase: Cell growth and normal functions.
      • S Phase: Synthesis phase; DNA is replicated.
      • G2 Phase: Further growth and preparation for mitosis.
    • M Phase (Mitotic Phase): Actual division of the cell, which includes mitosis and cytokinesis.
      • Prophase: Chromosomes condense and become visible.
      • Prometaphase: The nuclear envelope breaks down; spindle fibers attach to kinetochores on chromosomes.
      • Metaphase: Chromosomes align at the metaphase plate.
      • Anaphase: Sister chromatids are pulled apart to opposite sides of the cell.
      • Telophase: Nuclear envelopes reform around the separated chromatids.

  • Chromosome Structure

    • Chromosomes are made up of chromatin (DNA wrapped around histone proteins).
    • In S Phase, each chromosome consists of two sister chromatids.
    • Chromosomes should be properly condensed to allow for easier movement during cell division.

  • Importance of Checkpoints in the Cell Cycle

    • Three main checkpoints control progression through the cell cycle:
      1. G1 Checkpoint: Checks for cell size, nutrients, growth signals, and DNA integrity.
      2. G2 Checkpoint: Checks for successful DNA replication and DNA integrity.
      3. M Checkpoint: Ensures chromosomes are properly attached to spindle fibers before separation.
    • Tumor Suppressor Proteins: Such as p53, can trigger cell cycle arrest or apoptosis if DNA damage is detected.

  • Cancer and Cell Division

    • Cancer cells often bypass normal cell cycle controls, leading to uncontrolled division.
    • Benign Tumors: Non-invasive, localized growths.
    • Malignant Tumors: Invasive and can metastasize, spreading to other body parts.
    • Factors leading to uncontrolled cell division can include mutations in tumor suppressor genes and the overproduction of growth factors.

  • MPF (M Phase Promoting Factor)

    • Composed of Cyclin and CDK (cyclin-dependent kinase).
    • The levels of cyclins fluctuate, influencing the progression through the cell cycle.
    • Active when cyclin binds to CDK, initiating M phase and leading to mitosis.

  • Conclusion

    • Understand the cyclin-CDK relationship and the importance of checkpoints in regulating the cell cycle to prevent cancer.
    • Be prepared to elaborate on each phase of the cell cycle, checkpoint functions, and the implications of uncontrolled cell division.