52 Chapter 2. What’s inside cells[[Student version, December 8, 2002]]
Figure 2.23:(Fluorescence micrograph.) Newt lung cell in which the DNA is stained blue and microtubules in
the cytoplasm are stained green. This network of rigid filaments helps the cell maintain its proper shape, as well as
supplying the tracks along which kinesin and other motors walk. Chapter 10 will discuss these motors. [Copyrighted
figure; permission pending.]
Figure 2.24: (Drawing, based on molecular-dynamics simulations.) Space-filling model of an artificial bilayer
membrane. Imagine repeating the arrangement of molecules upward and downward on the page, and into and out
of the page, to form a double layer. The phospholipid molecules are free to move about in each layer, but remain
oriented with their polar head groups facing outward, toward the surrounding water. Chapter 8 will discuss the self-
assembly of structures like these. As with any molecular structure, keep in mind when looking at this picture that
things are not really static: The molecules are in constant, riotous, thermal motion. [Copyrighted figure; permission
pending.]