The final piece of the puzzle—how molecules such as sugar or ions pass in and out of the lipid bilayer, and how the cell communicates with its outside—was solved in 1972, nearly fifty years after Gorter and Grendel’s experiments. Two biochemists, Garth Nicolson and Seymour Singer, proposed a model in which proteins were embedded, like hatches, or channels, crossing the cell membrane. The lipid bilayer was not uniform or monotonous; it was porous by design. Proteins, floating in the membrane and spanning from inside to outside, allowed molecules to permeate the membrane and allowed other
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