Size and sequence matters
Figure 3. The relative electron-transfer rate versus the length of the DNA sequence as measured in experiments by Michel-Beyerle's group at Munich and Giese's group at Basel (red).
The sequence of bases between the donor and acceptor molecules is denoted next to each experimental point. In coherent transport (green line), the electron tunnels from the donor to the acceptor in a single step without becoming localized on an intermediate site.
Charge carriers can tunnel quickly through short DNA strands composed of AT base pairs, but the rate decreases exponentially with sequence length. At longer length scales, charge carriers tend to hop from one GC pair to another (blue line). This incoherent mechanism allows charge to move through much longer DNA strands.
The green and blue lines, and the purple points, are from quantum-mechanical computation models by Alex Burin and Yuri Berlin, who work with one of the authors (MR) at Northwestern.