cell biology

Overview of Cell Division

  • Focus areas: Mitosis and Meiosis

Cell Cycle Phases

  1. Interphase

    • Composed of three sub-phases: G1, S, G2.

    • G1 Phase: Initial growth phase.

    • S Phase: DNA replication occurs where DNA makes identical copies.

    • G2 Phase: Further growth and preparation for mitosis; includes checkpoints.

  2. Mitosis

    • Division of somatic cells (body cells).

    • Consists of the following stages:

      • Prophase: Chromosomes become visible; nuclear membrane begins breaking down; spindle fibers start to form.

      • Metaphase: Chromosomes align in the center of the cell (metaphase plate).

      • Anaphase: Chromatids are pulled apart to opposite ends of the cell.

      • Telophase: Nuclear membranes reform around the two sets of chromosomes; begins cytokinesis.

    • Cytokinesis: Final division of the cytoplasm, resulting in two genetically identical daughter cells.

  3. Meiosis

    • Division that produces gametes (sperm and egg cells).

    • Two main stages (each with its own phases): Meiosis I and Meiosis II.

      • Meiosis I includes:

      • Prophase I: Homologous chromosomes pair up (synapsis); crossing over occurs (genetic variation).

      • Metaphase I: Chromosomes align at the metaphase plate; independent assortment leads to variability.

      • Anaphase I: Homologous chromosomes are pulled apart.

      • Telophase I: Two new cells form, each with half the number of chromosomes (haploid).

      • Meiosis II is similar to mitosis:

      • Prophase II: Chromosomes condense and become visible again.

      • Metaphase II: Chromosomes align at the metaphase plate.

      • Anaphase II: Sister chromatids are pulled apart.

      • Telophase II: Four genetically diverse gametes are produced.

    • Emphasis on genetic variation from crossing over and independent assortment.

Key Definitions

  • Diploid (2n): A cell with two complete sets of chromosomes, one from each parent (e.g., somatic cells).

  • Haploid (n): A cell with one complete set of chromosomes (e.g., gametes).

  • Homologous Chromosomes: Chromosome pairs, one from each parent, that are similar in shape, size, and genetic content.

  • Chiasmata: The point of crossover between homologous chromosomes where genetic material is exchanged during prophase I of meiosis.

  • Independent Assortment: The random distribution of maternal and paternal chromosomes into gametes during meiosis.

Importance of Checkpoints in the Cell Cycle

  • Checkpoints ensure that cells only proceed to the next phase if they are ready and conditions are favorable.

  • Proto-oncogenes: Normal genes that help regulate cell growth and division.

  • Oncogenes: Mutated proto-oncogenes that can lead to uncontrolled growth and tumor formation when activated.

  • Tumor Suppressor Genes: Genes that monitor and regulate cell division; example includes p53, which acts as a checkpoint.

Cancer and Mutations

  • Discussed the role of oncogenes and tumor suppressor genes in cancer development, particularly focusing on the consequences of a mutated p53 gene.

  • Key points:

    • Proto-oncogenes become oncogenes through mutation.

    • Tumor suppressor genes (like p53) typically prevent uncontrolled cell division and promote apoptosis in damaged cells.

    • Loss of function in tumor suppressor genes leads to increased risk of cancer due to unchecked cell division.

Laboratory Techniques

  • Staining techniques are essential for observing cells under a microscope. Different stains can highlight specific cell components:

    • Fluorescent stains can target specific areas such as cell walls or nuclei, enhancing visibility of the chromosomes during the cell cycle.

  • Common microscopy observations include:

    • Chromatin is visible during interphase.

    • Distinct chromosomes appear in prophase.

Summary of Learning Outcomes

  • Students must:

    • Identify each stage of both mitosis and meiosis and describe the key events.

    • Understand the importance of genetic variation from meiosis and the implications for evolution and adaptation.

    • Know the function and effect of oncogenes and tumor suppressor genes in cell growth regulation and cancer prevention.