The present invention provides compositions and methods for transferring phospholipids and other molecules between the leaflets of a cell membrane. The compositions comprise at least one nucleic acid or compound having a hydrophilic region, where the composition is able to form a nanostructure that forms a toroidal pore in a lipid membrane. The nucleic acid or hydrophilic region-containing compound further contains an attached molecule capable of inserting the nanostructure into the lipid membrane. The invention also provides methods for scrambling lipids and other molecules in a cell membrane, which can be used to alter the function of a selected cell or to facilitate the death of the cell. The scrambling activity of synthetic scramblases described herein outperforms previously known enzymatically active DNA nanostructures and naturally occurring scramblases, in some cases by several orders of magnitude.