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.