A&P VM 5

Overview of the Cell Cycle

  • Cells continually divide to replace old or damaged cells, necessitating a process known as the cell cycle.

Stages of the Cell Cycle

G1 Phase (Gap 1)

  • Occurs first in the cell cycle. Cells grow and perform protein synthesis.

    • Key Functions:

      • Protein synthesis

      • Metabolism

      • Cellular respiration (produces ATP)

  • Waste buildup occurs; cells may remain in G1 phase indefinitely.

  • Non-dividing cells examples:

    • Brain cells do not increase in number but grow in size and connections.

    • Skeletal muscle cells do not undergo mitosis but grow in size and strength.

S Phase (Synthesis)

  • Following G1, cells enter S phase to prepare for division.

    • Key Functions:

      • DNA replication occurs; chromosomes replicate from 46 to 92.

    • Chromosomes consist of chains of DNA wrapped around proteins.

  • Factors causing cells to enter S phase:

    1. Cells grow too large; membrane cannot transport nutrients or remove waste efficiently.

    2. Accumulation of waste products.

    3. Genetic instructions dictate how many times a cell can divide (e.g., blood cells).

G2 Phase (Gap 2)

  • Occurs after S phase; preparation for mitosis.

    • Key Functions:

      • Energy and enzymes necessary for cell division are produced.

      • Histones (proteins) are synthesized to support the chromosome structure.

Interphase

  • Comprises G1, S, and G2 phases; cells are not actively dividing.

  • Key features include a nucleus with a membrane and visible chromosomes during certain phases.

Mitosis Stages

Prophase

  • First stage of mitosis; chromosomes condense and become visible.

    • Early Prophase: Chromosomes begin to thicken, remnants of the nuclear membrane are visible.

    • Late Prophase: Chromosomes are fully condensed, and the nuclear membrane disappears.

Metaphase

  • Chromosomes align along the cell's equatorial plane.

    • Key Structure: Spindle fibers attach to centrioles and pull chromosomes.

Anaphase

  • Sister chromatids are pulled apart toward opposite poles of the cell.

  • Transition is characterized by the separation of chromatids.

Telophase

  • Final stage of mitosis; chromosomes reach opposite poles and start to de-condense.

    • Key Feature: Formation of a cleavage furrow indicating that the cell is preparing to split into daughter cells.

Conclusion

  • After mitosis, two daughter cells are formed, each typically identical to the original cell.

  • Students will use microscopes to identify these phases in lab sessions, focusing on their distinct characteristics.