Which phase of the cell cycle is the most metabolically active?
Cellular metabolism is tightly coupled to cell cycle progression, with G1 phase exhibiting maximal biosynthetic activity to support doubling of mass before DNA replication. Upon growth factor binding, PI3K-Akt-mTORC1 pathway stimulates glucose uptake through GLUT1, increases glycolytic flux and pentose phosphate pathway for nucleotide precursors, enhances mitochondrial biogenesis via PGC1-alpha and mitochondrial transcription factor TFAM, and activates ribosome biogenesis through RNA polymerase I mediated rDNA transcription and S6K phosphorylation of ribosomal protein S6. Translation initiation factor eIF4E cap-binding protein synthesizes cyclins, CDKs, replication factors Cdt1, Cdc6, and histone chaperones. Lipid synthesis provides membrane for organelle growth, while amino acid transport sustains protein synthesis. By contrast, S phase devotes resources to dNTP synthesis, M phase shuts transcription, and G0 quiescent cells greatly reduce metabolic rate. Therefore G1 concentrates growth, accumulating tubulin, actin, and centrosome components monitored by size-sensing pathways. 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.
Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 17: G1 Metabolism and Growth.