The Temporal Architecture of Human Cells: Organelle Clocks and Distributed Circadian Time

For decades, eukaryotic circadian timing has been framed mainly through nuclear transcription-translation feedback loops (TTFLs). Here, we synthesize evidence supporting a broader organelle-centered model in which cellular time emerges from dynamic coupling between TTFL clocks, post-translational feedback loop (PTFL) oscillators, and entrained rhythmic modules across mitochondria, endoplasmic reticulum, lysosomes, peroxisomes, Golgi apparatus, plasma membrane, and cytoskeleton. Metabolic flux, redox cycling, proteostasis, ion handling, membrane excitability, trafficking, and mechanotransduction act as temporal currencies that either sustain selected transcription-independent rhythms or transmit phase information within a TTFL-coordinated network. In this layered architecture, the TTFL remains a central integrator that stabilizes inter-organelle phase relationships, aligns intracellular rhythms with environmental Zeitgebers, and links biochemical state to epigenetic and RNA-based regulation. We propose that circadian dysfunction reflects progressive intracellular desynchronization rather than isolated clock-gene failure, opening diagnostic and therapeutic opportunities aimed at restoring subcellular temporal coherence.