G1 Phase
G1 நிலை
Most students mistake G1 for a resting phase. It is the most metabolically active period of the cell cycle. If a cell fails to regulate G1, it loses control over its own destiny—leading directly to oncogenesis.
The idea
G1 phase is the interval between mitosis and the initiation of DNA replication. During this phase, the cell is metabolically active and continuously grows in size. It synthesizes necessary proteins, RNA, and organelles required for the subsequent S phase. The cell prepares its machinery for DNA duplication.
Why it matters
It allows the cell to accumulate resources and reach a critical size before committing to the energy-intensive process of DNA replication.
NEET lens
NEET focuses on the metabolic state and the timing of G1 relative to S phase. Remember: DNA content remains 2C, but cell size increases. Do not confuse G1 with G0; G0 is a quiescent stage, while G1 is active preparation. Expect questions on protein synthesis and organelle duplication here.
Clinical significance
The G1 checkpoint, or 'Restriction Point', is the critical gatekeeper. Mutations in proteins like p53, which monitor this phase, allow cells with damaged DNA to bypass the checkpoint. This leads to the uncontrolled proliferation characteristic of malignant tumors.
Introduction
G1 phase (Gap 1 or First growth phase) is the first phase of interphase, between completion of the previous cell division and the start of DNA replication, characterized by cell growth and preparation for S phase.
Core concept
Events in G1: cell grows (volume increases), protein synthesis, organelle biogenesis, assembly of replication machinery. G1 duration is most variable: rapidly dividing cells = short G1 (~1-2 hrs); slowly dividing cells = long G1 (days to years); permanently non-dividing cells exit to G0. G1/S checkpoint (restriction point): regulated by Rb protein, cyclin D-CDK4/6, and p53. Once past this checkpoint, cell is committed to divide.
Go deeper
Restriction point (in animals): the point in late G1 beyond which the cell no longer needs external growth factors to complete the cell cycle. Passing the restriction point = commitment to division. Before it: remove growth factors → cell arrests. After it: remove growth factors → cell completes division anyway.
From Class 10
Between one cell division and the start of DNA replication, cells have a growth period. This is G1 phase.