Cell cycle

What is cell cycle?

The cell cycle is a series of ordered events that a cell goes through from the time it is formed until it divides into two daughter cells. It encompasses the cell's growth, DNA replication, preparation for division, and the actual division process.

The cell cycle is essential for cell growth, development, and reproduction. It ensures that genetic material is accurately duplicated and distributed to daughter cells. The cell cycle is divided primarily into two broad phases:

1. Interphase

• The longest phase, sometimes called the "resting phase" but actually very active.

• The cell grows and prepares for division.

• Interphase is subdivided into three stages:

  • G1 phase (Gap 1): The cell grows physically, produces RNA, proteins, organelles, and carries out normal metabolic activities. It prepares for DNA replication but does not replicate DNA yet.

  • S phase (Synthesis): DNA replication occurs, duplicating the cell's chromosomes. Each chromosome now consists of two sister chromatids.

  • G2 phase (Gap 2): The cell continues to grow and produces proteins and organelles necessary for mitosis. The cell also begins reorganizing its contents to prepare for division.

Cells that do not divide can enter a resting phase called G0, where they remain metabolically active but do not progress through the cell cycle unless stimulated.

2. M Phase (Mitotic Phase)

• The phase of actual cell division.

• It includes:

  • Mitosis: Division of the cell’s nucleus and its genetic content into two nuclei.

  • Cytokinesis: Division of the cytoplasm, creating two daughter cells.

Checkpoints in the Cell Cycle

The cell cycle has built-in checkpoints to ensure the process proceeds correctly:

• G1 checkpoint: Determines if the cell is ready for DNA synthesis.

• G2 checkpoint: Checks for DNA damage and completeness of DNA replication before mitosis.

• Metaphase checkpoint (during M phase): Ensures chromosomes are properly aligned before division proceeds.

Major events of the cell cycle

Phase	Description	Key Activities
G1 Phase	Cell growth and metabolism	RNA and protein synthesis; organelle production
S Phase	DNA replication	Duplication of chromosomes
G2 Phase	Preparation for mitosis	Synthesis of proteins, organelles; cell growth
M Phase	Cell division (mitosis + cytokinesis)	Nuclear division and cytoplasmic division
G0 Phase	Resting/non-dividing phase	Cells exit cycle temporarily or permanently

Cell cycle regulation read here

Cell division read here