Phases of Cell Cycle — Core Principles
Core Principles
The cell cycle is the life story of a cell, from its birth to its division into two new cells. It's broadly divided into two main acts: Interphase and M-phase. Interphase is the long preparatory stage, where the cell grows and duplicates its genetic material.
It has three sub-phases: G1 (growth and protein synthesis), S (DNA replication, where DNA content doubles but chromosome number stays the same), and G2 (further growth and preparation for division). Following interphase is the M-phase, the actual division stage.
M-phase consists of karyokinesis (nuclear division) and cytokinesis (cytoplasmic division). Karyokinesis is further broken down into Prophase (chromosomes condense, nuclear envelope breaks down), Metaphase (chromosomes align at the equatorial plate), Anaphase (sister chromatids separate and move to opposite poles), and Telophase (nuclear envelopes reform, chromosomes decondense).
Finally, cytokinesis physically divides the cell into two daughter cells. Some cells may exit the cycle from G1 and enter a non-dividing state called G0.
Important Differences
vs Interphase and M-phase
| Aspect | This Topic | Interphase and M-phase |
|---|---|---|
| Duration | Longer (approx. 90-95% of cell cycle) | Shorter (approx. 5-10% of cell cycle) |
| Metabolic Activity | Highly metabolically active; growth, synthesis of proteins and organelles | Metabolically less active; primary focus on division |
| DNA State | DNA replication occurs (S phase); DNA is in chromatin form (decondensed) | DNA is condensed into visible chromosomes; segregation of chromosomes occurs |
| Key Events | Cell growth, DNA synthesis, organelle duplication, preparation for division | Nuclear division (karyokinesis) and cytoplasmic division (cytokinesis) |
| Visibility of Chromosomes | Chromosomes are not individually distinguishable (as chromatin) | Chromosomes are condensed and clearly visible under a microscope |
| Purpose | Preparation for cell division, ensuring genetic material is duplicated | Actual segregation of genetic material and formation of daughter cells |