Cell Cycle
செல் சுழற்சி
A cell does not simply split in two. It executes a highly regulated, sequential program to duplicate its genome and organelles. If this sequence falters, you are looking at the birth of a malignancy, not a healthy daughter cell.
The idea
The cell cycle is the orchestrated sequence of events involving genome duplication, synthesis of cellular constituents, and eventual division into two daughter cells. It is a fundamental process ensuring genetic continuity. The cycle is divided into distinct phases, strictly controlled to prevent errors in DNA replication. Every component must be synthesized before the cell commits to cytokinesis.
Why it matters
It exists to ensure the orderly duplication and distribution of genetic material and cellular components to maintain life across generations.
NEET lens
NEET focuses on the definition and the sequence of events. Do not confuse 'genome duplication' with 'cytokinesis'. Remember, the cell cycle is a continuous process, but we study it in phases for clarity. Expect questions on the chronological order of these events.
Clinical significance
Uncontrolled cell cycle progression is the hallmark of cancer. When regulatory checkpoints fail, cells divide indefinitely, forming tumors. Understanding the cell cycle is the basis for chemotherapy, which targets rapidly dividing cells to halt malignant growth.
Introduction
The cell cycle is the ordered series of events by which a cell duplicates its contents and divides into two daughter cells. It is fundamental to growth, repair, and reproduction in all living organisms.
Core concept
Two major phases: Interphase (preparation, majority of time) and M phase (division). Interphase = G1 + S + G2. M phase = mitosis + cytokinesis. Three key checkpoints ensure accuracy: G1/S checkpoint (Is DNA intact? Enough nutrients?), G2/M checkpoint (Is DNA fully replicated?), Spindle assembly checkpoint (Are all chromosomes attached?). Cyclins/CDKs regulate transitions.
Go deeper
Cell cycle duration varies enormously: rapidly dividing cells (intestinal epithelium) ~12 hours, typical cultured cells ~24 hours, some embryonic cells (early frog embryo) as fast as 30 minutes (no G1 or G2). Nerve cells and muscle cells permanently in G0.
From Class 10
Living cells divide to grow and reproduce. The complete sequence of growth and division that a cell goes through is called the cell cycle.