  The functionality of many biological systems depends on reliable electron
transfer with minimal heating. Unlike man-made electric circuits, nature
realizes electron transport via insulating chiral molecules. Here we include
spin into the analysis of tunneling through these molecules, and demonstrate
its importance for efficient transport. We show that the helical geometry
induces robust spin filtering accompanied by, and intimately related to,
strongly enhanced transmission. Thus, we resolve two key questions posed by
transport measurements through organic molecules, demonstrating their common
origin.
