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Bio Tool #5 · Biology I Module 2 · SOL BIO.3d

The Membrane Patch

Start with two thin sheets of water and build a piece of cell membrane between them, one kind of molecule at a time: phospholipids, cholesterol, three proteins with three different jobs, and the fibres that hold the patch in place on each side. Predict before every step, then act and watch. Turn the patch with a finger at any point: straight down it is a mosaic, edge-on it is a bilayer. About twenty-five minutes.

Nothing is submitted. Progress saves on this device, so a second sitting picks up where the first stopped. In my own college cell-biology classes, the topics students named hardest were pumps moving ions against a gradient, passive versus active transport, and how the membrane stays fluid. Steps 3 to 6 are built around those three.

Lipid: dark red circle head, tan capsule tails Cholesterol (also a lipid): green rings, so it stands out Protein: rounded cylinder Carbohydrate: hexagon = one sugar Nucleic acid: ATP, built like a nucleotide
Outside the cell Inside the cell (cytoplasm)
or drag to turn it

Every shape here is a real structure you can turn in Mol*

  • 1J4N Aquaporin-1, the real water channel. Four copies sit side by side; look down the middle of any one of them to find its pore.
  • 2ZXE The sodium-potassium pump. A cholesterol molecule is bound in this structure; look for it against the part that sits in the membrane.
  • 2RH1 A receptor that sits in the membrane, the β2-adrenergic receptor. Part of it was replaced by an engineered piece so that it would form crystals.
  • 1IR3 The inside half of the insulin receptor, the part that moves phosphates onto proteins,The kinase half of the insulin receptor, with an ATP look-alike sitting where ATP binds.
  • 3J8A An actin filament, with tropomyosin wrapped along it.
  • molstar.org Mol* is free and open source; paste any PDB ID.