Key Cell Cycle Phases to Know for Molecular Biology

The cell cycle is a series of phases that cells go through to grow and divide. Understanding these phases—G1, S, G2, and M—helps us grasp how cells replicate their DNA and ensure proper distribution of genetic material during division.

1. G1 phase (Gap 1)

   • The cell grows in size and synthesizes proteins necessary for DNA replication.
   • Organelles are duplicated to prepare for cell division.
   • The cell assesses its environment and checks for DNA damage before proceeding to the next phase.

2. S phase (Synthesis)

   • DNA replication occurs, resulting in two identical sets of chromosomes.
   • Each chromosome is now composed of two sister chromatids.
   • The cell continues to grow and produce proteins required for cell division.

3. G2 phase (Gap 2)

   • The cell undergoes further growth and prepares for mitosis.
   • Additional proteins and organelles are synthesized, ensuring the cell is ready for division.
   • The cell checks for any DNA replication errors and repairs them before entering mitosis.

4. M phase (Mitosis)

   • The process of cell division occurs, resulting in two daughter cells.
   • Mitosis is divided into several stages: prophase, metaphase, anaphase, and telophase.
   • The cell's genetic material is evenly distributed to ensure each daughter cell receives a complete set of chromosomes.

5. Interphase

   • The phase that includes G1, S, and G2, where the cell spends the majority of its life cycle.
   • The cell prepares for division while performing its normal functions.
   • Interphase is crucial for growth, DNA replication, and preparation for mitosis.

6. Prophase

   • Chromatin condenses into visible chromosomes, and the nuclear envelope begins to break down.
   • The mitotic spindle forms, and spindle fibers extend from centrosomes.
   • Chromosomes begin to move toward the cell's equatorial plane.

7. Metaphase

   • Chromosomes align at the cell's equator, known as the metaphase plate.
   • Spindle fibers attach to the centromeres of the chromosomes.
   • This alignment ensures that each daughter cell will receive an identical set of chromosomes.

8. Anaphase

   • Sister chromatids are pulled apart and move toward opposite poles of the cell.
   • The spindle fibers shorten, ensuring equal distribution of genetic material.
   • This phase is critical for maintaining the correct chromosome number in daughter cells.

9. Telophase

   • Chromatids reach the opposite poles and begin to de-condense back into chromatin.
   • The nuclear envelope re-forms around each set of chromosomes.
   • The cell prepares for the final separation into two distinct daughter cells.

10. Cytokinesis

    • The cytoplasm divides, resulting in two separate daughter cells.
    • In animal cells, a cleavage furrow forms, pinching the cell membrane.
    • In plant cells, a cell plate forms, leading to the development of a new cell wall.