222 Chapter 7. Entropic forces at work[[Student version, January 17, 2003]]
Figure 7.2: (Drawing, based on structural data.) It’s crowded’s insideE. coli.For clarity, the main part of the
figure shows only the macromolecules; the lower right inset includes smaller molecules as well (water molecules,
however, are still omitted).Left side,astrand of DNA (far left) is being transcribed to messenger RNA, which is
immediately translated into new proteins by ribosomes (largest objects shown). Between the ribosomes, proteins of
many shapes and sizes are breaking down small molecules for energy, and synthesizing new molecules for growth and
maintenance. The region depicted is about 100nm× 100 nm.[From Goodsell, 1993.]
arab
Figure 7.3:(Schematic.) Origin of the depletion interaction. (a)Twosurfaces of matching shape separated by
more than twice the radiusaof some suspended particles. Each surface is surrounded by a depletion zone of thickness
a(dashed lines).(b)When the surfaces get closer than 2a,the depletion zones merge and their combined volume
decreases.