Q.11 Which one of the following statements about the G1 checkpoint of eukaryotic cell
division cycle is INCORRECT?
(A) Cell assures the existence of favorable extracellular environment
(B) Cell assures the DNA has no damage
(C) Cell assures the damaged DNAs are directed for repair mechanism
(D) Cell assures complete replication of DNA

The incorrect statement is (D) Cell assures complete replication of DNA.​

G1 checkpoint, also called the restriction point or G1/S checkpoint, occurs at the end of G1 phase before S phase entry in the eukaryotic cell cycle. This control point evaluates key readiness factors to prevent flawed DNA replication.​

Option Analysis

Option (A): Correct. The cell assesses favorable extracellular signals like growth factors and nutrients to commit to division. Without these, cells enter G0 quiescence.​

Option (B): Correct. DNA integrity is checked for damage via p53-dependent and independent pathways; severe damage triggers arrest or apoptosis.​

Option (C): Correct. Detected damage activates repair via checkpoint kinases (ATM/ATR), halting progression until fixed or irreparable.​

Option (D): Incorrect. G1 precedes S phase, so DNA replication has not occurred; completion is verified at G2/M checkpoint post-S phase.​

The G1 checkpoint eukaryotic cell division cycle serves as a critical control mechanism ensuring cells only proceed to DNA synthesis when conditions support genomic fidelity. This G1 checkpoint evaluates growth signals, cell size, and DNA integrity before S phase commitment, preventing errors that could lead to cancer or cell death.​

Key Functions

• Monitors favorable extracellular environment via mitogenic signals; absence directs to G0.​

• Verifies DNA has no damage using sensors like MRN complex and p53 pathway.​

• Activates damaged DNA repair mechanisms through ATM/ATR kinases for arrest and resolution.​

• Prepares proteins and energy for replication without checking completion (handled in G2).​

MCQ Insights for CSIR NET

In exams, errors often confuse G1 with G2: complete replication of DNA occurs post-S at G2/M, not G1. Rb-E2F regulation and cyclin-CDK complexes drive passage.​

Dysregulation links to oncogenesis, making this vital for molecular biology and cell cycle studies.​