CrowdedRoom

A slice of a crowded cell

Shapes are kinds of molecule, not particular ones: ribosomes (the big protein-making machines), other proteins, strands of RNA and water. Not to scale, and far emptier than a real cell.

How full is a real cell? Inside the bacterium E. coli, every litre of the cell's insides holds about 300 to 400 grams of big molecules (Zimmerman and Trach, 1991). And a protein called GFP spreads out about 11 times more slowly inside E. coli than it does in water (Elowitz and colleagues, 1999).

The game

Toy model A simplified picture to show one idea. Not a measurement, and not a prediction. Of crowding: one small molecule stepping at random on a flat grid of squares, where a real cell is 3D and full of moving molecules.

The grid is 15 squares by 15. The small molecule (a circle) starts in one corner. Its partner (a square) sits still. Each step, the small molecule gets bumped one square up, down, left or right, at random. If that square holds a crowder (a dark block) or the wall, it stays put, but the step still counts. It stops when it lands next to the partner. We run it 200 times and give the average.

1. Crowded (crowders on about 35 of every 100 squares)

   Your guess first: how many steps, on average?

   under 500 steps500 to 1,000 steps1,000 to 2,500 stepsover 2,500 steps

2. Some crowd (crowders on about 20 of every 100 squares)

   Your guess first: how many steps, on average?

   under 500 steps500 to 1,000 steps1,000 to 2,500 stepsover 2,500 steps

3. Empty room (no crowders)

   Your guess first: how many steps, on average?

   under 500 steps500 to 1,000 steps1,000 to 2,500 stepsover 2,500 steps