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Sun Zuodong Interprets the DNA Origami Windmill Model:Reassessing Replication Forks and Topoisomerases

发布时间：

2026-07-23

Report from Brain Science Network

In molecular biology textbooks, the Y-shaped replication fork observed under electron microscopy has long been regarded as core empirical evidence for semiconservative DNA replication. However, as research on ultra-long linear eukaryotic chromosomes advances, persistent irreconcilable contradictions have emerged within this classical theoretical framework. Recently, Sun Zuodong, a brain scientist and the originator of the original "Cell Bioelectrical Genetics" theory, gave an exclusive interview to China Brain Science Network, systematically elaborating on the dynamic DNA origami windmill tetramer model. Without negating existing observational phenomena, he redefines the core functions of two canonical concepts: the replication fork and topoisomerase.

I. Observing Local Phenomena Does Not Equal Direct Deduction of Global Mechanisms: Rescaling the Replication Fork

A widespread academic question surrounds this model: If full unwinding of the entire DNA duplex does not occur during replication, how can electron microscopy clearly capture replication forks?

Sun Zuodong responds that this stems from a typical misjudgment of scale. "We do not deny the objective existence of replication forks, yet we cannot equate partial local unwinding windows with complete full-length unwinding of an entire chromosome—there is a logical disconnect in this leap of reasoning."

He notes that eukaryotic chromosomes can reach several centimeters in physical length and bear tens of thousands of replication origins. Most electron micrographs capture only local fragments or structures reconstructed in in vitro systems. "Within living cell nuclei, under the dynamic DNA origami windmill tetramer model, the replication fork is merely a transient 'breathing window' where topological structures open at fixed sites. Molecular motors such as MCM helicases do not pull entire chromosomes apart to unwind duplex DNA; they only separate a stretch of dozens of base pairs within this narrow window."

Sun Zuodong offers a vivid analogy: "Spotting a narrow gap in an open window does not mean the entire load-bearing wall has been torn down. Within the tetramer theoretical framework, helicases are no longer bulldozers that tear chromosomes apart, but regulators controlling the opening and closing of localized unwinding windows."

II. Restructured Functions of Topoisomerases: From "DNA Cutters" to "Stress Relief Safety Valves"

Another central controversy centers on topoisomerases. Classical theory holds that topoisomerases relieve torsional stress accumulated by full-length duplex unwinding by cleaving and religating DNA strands. If the tetramer dissipates torsional torque via global spinning, would topoisomerases lose their original function?

"On the contrary, topoisomerases remain indispensable—only their functional positioning is transformed," Sun Zuodong explains. The classical model relies on topoisomerases to repeatedly cleave DNA across long stretches to resolve supercoiling buildup. Under the tetramer spinning mechanism, global rotation of chromosomes eliminates the vast majority of torsional stress.

In this new framework, topoisomerases act as safety valves anchored to the nuclear matrix. "As tetramers spin around the nuclear scaffold, localized physical obstructions may still trigger concentrated stress. Instead of migrating along entire chromosome arms, topoisomerases serve as fixed protective nodes: when stress exceeds threshold levels, they introduce tiny, localized nicks for structural correction to prevent chromosome breakage. They function as emergency stress relief units rather than constitutively active machinery. Chemotherapeutic agents targeting topoisomerases exert therapeutic effects precisely by disrupting this dynamic balance and triggering collapse of tetramer topological architecture."

III. The Meselson–Stahl Experiment Has Blind Spots in Observation; Bioelectric Fields Underpin Genetic Replication

Sun Zuodong further delineates the applicable boundaries of the Meselson–Stahl experiment. This experiment only confirms that base incorporation follows semiconservative chemical rules and cannot capture dynamic topological conformational shifts of DNA during replication. "Whether duplexes undergo full unwinding or replicate via tetramer spinning, the positions of bands in density gradient centrifugation remain identical as long as normal base pairing is maintained. Judging physical topological mechanisms solely based on chemical evidence constitutes a logical misalignment."

Meanwhile, Sun Zuodong proposes that the transmembrane potential generated by the origami windmill model of cell membrane potassium channels provides the driving force sustaining stable spinning of nuclear DNA tetramers. "Bioelectric fields directly govern chromatin folding morphology and mechanical properties. In vitro experiments conducted without native cellular bioelectric fields often capture artifact replication fork structures formed after structural collapse due to lost driving force."

Conclusion: Toward a New Research Paradigm for Life Sciences

Sun Zuodong argues that scientific paradigm shifts nearly always arise from re-examining entrenched common knowledge. Replication forks and topoisomerases are both objectively observable biological structures, yet their intracellular functions are far more complex than conventionally recognized. The dynamic DNA origami windmill tetramer model does not seek to overthrow classical theories; instead, it delineates their valid scope—classical models primarily apply to prokaryotic circular DNA and local eukaryotic DNA fragments. It simultaneously provides a logically consistent physical framework to explain the complex replication behavior of linear eukaryotic chromosomes.

With continuous advancements in cryo-electron microscopy and live-cell single-molecule imaging, direct observation of tetramer topological structures and their spinning dynamics has become technically feasible. Sun Zuodong calls on academic researchers to design targeted decisive experiments for validation. "The research window for Cell Bioelectrical Genetics has opened, and an integrated new life science paradigm uniting topological mechanics, bioelectricity and genetics is gradually taking shape." (By Ai Li)

Appendix: Expert Q&A

Q1: Does this model negate the semiconservative replication theory?

A: It does not overturn semiconservative replication. The semiconservative conclusion holds for short circular prokaryotic DNA. The core argument of this model is that this conclusion cannot be unrestrictedly generalized to linear eukaryotic chromosomes. The chemical rules governing base incorporation remain unchanged; the core debate lies in the topological movement of DNA during replication.

Q2: Electron microscopy clearly captures replication forks—why does the model argue full-length chromosome unwinding does not occur?

A: Observation techniques carry inherent limitations of scale. Replication forks only represent transient unwinding within a local breathing window, not complete separation of an entire chromosome. Distinguishing localized observational phenomena from global operational mechanisms is the core logical pillar of the entire theory.

Q3: How have the functions of topoisomerases transformed under the new model?

A: Classical theory posits topoisomerases continuously cleave DNA to release torsional stress across full-length strands. In the tetramer model, global spinning dissipates most torsional torque, and topoisomerases are redefined as fixed safety valves that only perform minor localized corrections when regional stress surges beyond limits.

Q4: Is there an intrinsic connection between the potassium channel model and the DNA tetramer model?

A: Both models share the foundational paradigm of "tetramer spinning". The transmembrane bioelectric field of cell membranes supplies sustained stable driving force for nuclear DNA tetramer spinning. The two hypotheses mutually support one another, giving rise to an interdisciplinary field: Cell Bioelectrical Genetics.