32 Chapter 2. What’s inside cells[[Student version, December 8, 2002]]
Figure 2.3:(Drawing, based on electron microscopy.) Relative sizes (10^5 ×magnification). (a)Some molecules and
macromolecules (enlarged in Figure 2.4). (b)Abacterial cell (see Figures 2.1, 2.2a and 2.5). Visible structures include
flagella (trailing to the right), the nucleoid (white region in center), and the thick, rigid cell wall. The flagella propel
the bacterium by a mechanism discussed in Chapter 5; they are in turn driven by motors discussed in Chapter 11.
(c)Human immunodeficiency virus. (d)Abacterial virus, or “phage.” [From (Goodsell, 1993).] [Copyrighted figure;
permission pending.]
them to partition itself into separate compartments. (b)Cells useactive transportto bring synthe-
sized materials to particular destinations. (c)Biochemical processes are highlyspecific:Most are
mediated by enzymes, which select one particular target molecule and leave the rest alone.
2.1 Cell physiology
Roadmap Wewill begin our story by recalling some of the characteristic activities of living cells,
then turn to their overall structural features. The physical aspects of cell function and structure
are sometimes called “cell physiology.” Section 2.2 will turn to the ultimate molecular constituents
of cells, progressively building from the smallest to the largest. This approach is generally called
“molecular cell biology.” By this point we will have a beautiful, but static, picture of the cell as a
collection of architectural elements. To close the circle of logic, we’ll need to understand something
about how these elements get constructed, and more generally how the cell’s otheractivitiescome
about. Thus, Section 2.3 will introduce the world of “molecular devices.” This third aspect of
cellsisthe primary focus of this book,though along the way we will touch on the others, and even
occasionally go beyond cells to organisms.