Understanding the Cell Cycle

The Cell Cycle

  • The cell cycle is the series of events that cells go through as they grow and divide.
  • It is essential for organism growth, tissue repair, and replacement of old cells.

Main Phases of the Cell Cycle

  • The cell cycle consists of two primary phases:
    • Interphase
    • M Phase (Mitosis + Cytokinesis)

Interphase

  • Interphase is the preparation phase and comprises most of the cell's life.
Stages of Interphase:

  1. G1 Phase (Gap 1):

    • The cell grows and synthesizes proteins necessary for DNA and cell functions.
    • The cell performs routine metabolic processes and checks conditions to ensure they are favorable for DNA division.
    • Key question: Are conditions suitable for division?

  2. S Phase (Synthesis):

    • The cell replicates its DNA, ensuring each daughter cell will have an identical set of chromosomes.
    • This involves synthesizing the complete set of chromosomes.

  3. G2 Phase (Gap 2):

    • Further growth occurs, and the cell checks its DNA for errors.
    • The cell prepares for division by synthesizing proteins needed for mitosis and assembling structures required for cell division.

M Phase (Mitosis)

  • During M Phase, the cell divides its duplicated DNA into two new nuclei.
Stages of Mitosis:

  1. Prophase:

    • Chromosomes condense and become visible.
    • Spindle fibers emerge from the centrioles to assist in moving chromosomes.

  2. Metaphase:

    • Chromosomes align at the cell's equatorial plane (middle) and attach to spindle fibers.

  3. Anaphase:

    • Sister chromatids are pulled apart to opposite poles of the cell, ensuring that each new cell will receive one copy of each chromosome.

  4. Telophase:

    • New nuclear membranes form around the separated chromatid sets; chromosomes begin to uncoil back into chromatin.

Cytokinesis

  • The final step of cell division; the cytoplasm of the cell divides, creating two distinct daughter cells.
  • Each daughter cell contains its own nucleus, and the DNA is identical to that of the original cell.

Key Points to Remember

  • The cell cycle is tightly regulated to prevent errors, such as uncontrolled division which can lead to cancer.
  • It primarily applies to eukaryotic cells (found in plants, animals, and humans).
  • Some cells, such as nerve cells, may exit the cycle permanently and enter a resting phase known as G0 (Gap 0), where they stop dividing.