Bio111 Exam 2- Module 10- TAMU- Fletcher

🧠 CELL DIVISION & CYCLE – STUDY NOTES

Part 1: Somatic Cells, Gametes & Cell Division Types

Somatic Cells:

  • All body cells (except reproductive cells).

  • Diploid (2n) → two sets of chromosomes (one from each parent).

  • Example: skin, muscle, nerve cells.

Gametes:

  • Sex cells (sperm and egg).

  • Haploid (1n) → one set of chromosomes.

  • Combine during fertilization to form a diploid zygote.

Prokaryotic vs. Eukaryotic Cell Division:

  • Prokaryotes: Divide by binary fission (simple splitting of DNA and cytoplasm).

  • Eukaryotes: Divide by mitosis (for somatic cells) and meiosis (for gametes).

  • Both: Produce new cells from one parent cell and ensure genetic material is copied and distributed.

Part 2: The Cell Cycle & Mitosis

Cell Cycle Overview:
Divided into Interphase (growth & preparation) and the Mitotic Phase (M phase) (division).

1. Interphase

  • G₁ phase: Cell grows, performs normal functions.

  • S phase: DNA is replicated (each chromosome duplicated).

  • G₂ phase: Cell prepares for mitosis (organelles, proteins made).

2. Mitotic Phase

  • Includes Mitosis (division of nucleus) and Cytokinesis (division of cytoplasm).

Mitosis: 5 Stages

  1. Prophase:

    • Chromosomes condense and become visible.

    • Spindle fibers form; nuclear envelope begins to break down.

  2. Prometaphase:

    • Nuclear envelope fully disappears.

    • Spindle fibers attach to centromeres (via kinetochores).

  3. Metaphase:

    • Chromosomes align at the cell’s equator (metaphase plate).

  4. Anaphase:

    • Sister chromatids separate and move to opposite poles.

  5. Telophase:

    • Chromosomes de-condense; new nuclear envelopes form.

    • Spindle breaks down; cell prepares to divide cytoplasm.

Cytokinesis:

  • Division of the cytoplasm → two identical daughter cells.

  • In animal cells: cleavage furrow forms.

  • In plant cells: cell plate forms.

Function:

  • Mitosis: divides nucleus → ensures identical DNA in both daughter cells.

  • Cytokinesis: divides cytoplasm → completes cell division.

Part 3: Cell Cycle Regulation & Cancer

Cell Cycle Checkpoints:

  • Ensure proper cell growth, DNA replication, and division.

  • Purpose: prevent damaged or incomplete cells from dividing.

Three Major Checkpoints:

  1. G₁ Checkpoint (Restriction Point):

    • Checks for DNA damage, size, and nutrients.

    • If failed → cell enters G₀ (resting phase).

  2. G₂ Checkpoint:

    • Checks for proper DNA replication and damage repair.

    • Ensures readiness for mitosis.

  3. M Checkpoint (Spindle Checkpoint):

    • Ensures all chromosomes attached to spindle fibers before separation.

Positive vs. Negative Regulators:

  • Positive regulators: promote cell cycle progression.

    • Example: Proto-oncogenes (normal genes that stimulate division).

  • Negative regulators: inhibit cell cycle progression.

    • Example: Tumor suppressor genes (like p53).

  • When proto-oncogenes mutate → become oncogenes → uncontrolled growth.

  • When tumor suppressor genes mutate → cell loses ability to stop cycle → cancer.

Cancer Development:

  • Cancer: uncontrolled cell division caused by mutations in regulatory genes.

  • Caused by DNA damage, carcinogens, or inherited mutations.

  • Benign tumor: localized mass.

  • Malignant tumor: invades nearby tissues.

  • Metastatic cancer: spreads to other parts of the body.