Practice question

G2 phase operates as final growth and quality control interval preparing cells materially and regulatory for mitosis. After completion of DNA replication in S phase, cells enter G2 where synthesis continues: transcription of genes encoding tubulin isotypes, gamma-tubulin ring complex proteins gamma-TuRC, pericentrin, Cep192, and microtubule-associated proteins rises to stockpile building blocks for spindle assembly. Centrosomes duplicated in S phase mature by acquisition of pericentriolar material becoming competent microtubule organizing centers. Organelles including Golgi apparatus and mitochondria expand through lipid synthesis and fusion events driven by mitofusins. Checkpoint kinase ATR activated by persistent RPA-coated single-stranded DNA and Chk1 maintain inhibitory Wee1-dependent Tyr15 phosphorylation on CDK1, holding cyclin B-CDK1 inactive while replication finishes. When replication and repair complete, Cdc25 phosphatases remove inhibitory marks, triggering feedback amplification that drives lamina breakdown, chromosome condensation, and Golgi unlinking. G2 thus ensures daughters inherit complete genome and sufficient organelle mass. This circuitry is highly conserved across eukaryotes, integrating growth factor signals, DNA damage surveillance, and developmental cues, and its disruption frequently underlies oncogenesis, providing targets for checkpoint inhibitors and cancer therapeutics.