Electron transport through a short poly(GACT)–poly(CTGA) DNA ladder strand connected to semi-infinite metallic cumulene leads has been systematically investigated using Harrison’s tight-binding Hamiltonian and the Landauer–Büttiker approach. Our comparative analysis of single- and multi-electron transport reveals that all valence electrons injected into the DNA by the leads actively participate throughout the quantum transport process, necessitating the explicit incorporation of these contributions in transport models to achieve more accurate predictions. The transmission probability and current–voltage characteristics of the DNA molecule exhibit bioelectronic semiconducting behavior, influenced by both 𝜋- and the often-neglected 𝜎-electrons, and are highly sensitive to the coupling strength of the lead–molecule interface. Our findings demonstrate that the vertical coupling strength between the DNA base-pairs and the sugar–phosphate backbone plays a critical role in determining the semiconducting gap. Notably, at cryogenic lead temperatures, sharp step-like features are observed in the current–voltage characteristics of DNA, both with and without the backbone. These features may be explained by coherent transport, quantum tunneling, or hopping conduction of electrons along both ladder strands. As the lead temperature rises, the current–voltage curves become significantly smoother. These results are fully consistent with experimental observations and provide deeper theoretical insights into electron transport in DNA nanostructures.
