IB Bio Mitosis

IB Unit 5: Cell Division and Cancer

Overview of Cell Division

  • Cell Division: Essential process with critical regulation to maintain cellular function.

    • Must be controlled.

1.6.1 Stages of the Cell Cycle

  • Interphase: Active period in cell life.

    • G1 Phase (Gap 1): Increase in cell size, organelle production, protein synthesis.

    • S Phase (Synthesis): DNA replication occurs.

    • G2 Phase (Gap 2): Final preparations for mitosis, further growth.

  • Mitosis: Process of nuclear division.

  • Cytokinesis: Physical division of the cytoplasm (not part of mitosis).

1.6.2 Interphase Functions

  • Active metabolic reactions:

    • Protein synthesis

    • DNA replication

    • Increase in organelles (mitochondria & chloroplasts).

1.6.3 Chromosome Structure during Mitosis

  • Chromosome Condensation: Chromosomes condense by supercoiling to prepare for mitosis.

1.6.4 Role of Cyclins

  • Cyclins: Proteins involved in regulating the cell cycle.

    • Level of cyclin must reach a threshold for transition to the next stage of the cell cycle.

1.6.5 Phases of Mitosis

  • Prophase: Chromatin condenses to chromosomes; spindle fibers form.

  • Metaphase: Chromosomes align at the cell equator.

  • Anaphase: Sister chromatids separate and move to opposite poles.

  • Telophase: Nuclear membranes reform around separated chromosomes.

1.6.6 Cytokinesis in Plant vs. Animal Cells

  • Animal Cells: Contractile ring forms cleavage furrow; cells pinch apart.

  • Plant Cells: Vesicles fuse to form cell plate that develops into a new cell wall.

1.6.7 Identifying Phases in Micrographs

  • Use of microscopes to determine phases of mitosis in various slides.

1.6.8 Determining Mitotic Index from a Micrograph

  • Mitotic Index: Ratio of cells in mitosis to total number of cells.

    • Important for assessing cellular proliferation, especially relevant in cancer.

1.6.9 Definitions

  • Mutagens: Agents causing mutations in DNA that may result in cancer.

  • Oncogenes: Genes that, when mutated, can cause uncontrolled cell division leading to tumors.

  • Metastasis: Process by which cancer cells spread from the primary tumor to other parts of the body.

1.6.10 Correlation Between Smoking and Cancer

  • Smoking: Strong correlation with various cancers:

    • Lung, throat, mouth, and several others linked to chemical exposure.

Review of Cell Theory

  1. All organisms consist of one or more cells.

  2. Cells are the basic units of life.

  3. Cells arise only from pre-existing cells.

Reasons for Cell Division

  • Growth: Production of similar cells (muscle cells).

  • Injury Repair: Replacement of damaged cells.

  • Zygote Division: Initial cell division leading to multicellular organism, followed by differentiation.

  • Asexual Reproduction: Production of identical offspring through mitosis (e.g., hydra).

Chromosome Terminology

  • Centromere: Links sister chromatids.

  • Sister Chromatids: Duplicated chromosomes.

  • Centrioles: Organizing spindle microtubules.

  • Centrosome: Structure containing centrioles.

  • Telomere: Ends of chromosomes, important for chromosomal stability.

Coordination of Cell Division

  • Multi-cellular organisms must coordinate division across tissues, crucial for growth and maintenance.

    • Varies by cell type:

    • Embryo cell cycle < 20 minutes

    • Skin cells: Divide every 12-24 hours

    • Liver cells: Divide every 1-2 years

    • Mature nerve & muscle cells: No division after maturity (G0 phase).

Overview of DNA Organization for Division

  • Structure: DNA is organized as chromatin, which condenses into chromosomes for division.

  • Double Helix: DNA wrapped around histone proteins, forming a chromatin fiber.

Checkpoint Control System

  • Checkpoints: Mechanisms to assess completion of critical cellular processes.

    • G1/S Checkpoint: Determines if DNA synthesis can begin;

    • G2/M Checkpoint: Checks if DNA synthesis is complete correctly;

    • Spindle Checkpoint: Assesses if chromosomes are properly attached to spindle.

"Go-Ahead" Signals and Cyclins

  • Internal Signals: Cell growth and nutrition.

  • External Signals: Growth factors entrusting the cell division process.

  • Cyclins and Cdks: Cyclins activate cyclin-dependent kinases, which regulate the cell cycle transitions.

Cyclins Discovery

  • Discovered serendipitously by Tim Hunt studying mitosis in sea urchins.

    • Cyclins are crucial in controlling progression through the cell cycle.

Phases of Mitosis
Prophase

  • Chromatin condensation to sister chromatids.

  • Centrosomes move to opposite poles.

  • Nuclear membrane breaks down.

Metaphase

  • Chromosomes line up along the cell equator; spindle fibers attach to centromeres.

Anaphase

  • Separation of sister chromatids to opposite poles, now referred to as chromosomes.

Telophase

  • Chromosomes arrive at the poles, de-condensing into chromatin. Nuclear membranes reform.

Cytokinesis Details

  • Differentiates between plant and animal cells.

  • Animal Cells: Form cleavage furrow through contractile proteins.

  • Plant Cells: Form cell plate using vesicles from Golgi apparatus.

Mitotic Index Significance

  • Measures cellular proliferation.

  • Used in medicine for predicting cancer treatment responses; elevated mitotic indices indicate high cellular division related to abnormalities.

Cancer Development and Mutagens

  • Cancer: Abnormal growth of tissue; classified as benign or malignant tumors.

    • Benign: Localized growth without spreading.

    • Malignant: Can metastasize, impairing body functions.

  • Mutagens: Cause gene mutations, potential carcinogenic agents include radiation, chemicals, and certain biological agents.

Key Mutations Leading to Cancer

  1. Unlimited growth activation.

  2. Ignored checkpoints deactivation.

  3. Evading apoptosis.

  4. Immortality through chromosome maintenance genes.

  5. Promoting vasculature.

  6. Overcoming anchorage dependency.

Cause of Cancer "Hits"

  • Physical agents (radiation, UV light), chemicals, lifestyle factors (tobacco), age, and genetics contribute to mutational frequency.

Common Cancers in the U.S.

  • Projected diagnoses reveal varying prevalence:

    • 30.3% breast cancer

    • 12.3% lung cancer

    • 8.7% uterine cancer

    • 21.5% prostate cancer.

Primary vs. Secondary Tumors

  • Primary Tumor: Site of original cancerous growth.

  • Secondary Tumors: Result from metastasis, or spread of cancerous cells to new sites.

Correlation Between Smoking and Cancer Incidence

  • Strong connections with multiple cancers, particularly lung, mouth, throat, and others.

  • Evidence includes carcinogens in tobacco affecting health directly.