2.1. Cell physiology[[Student version, December 8, 2002]] 33
Figure 2.4:(Drawing, based on structural data.) Relative sizes of the objects shown in panel (a) of Figure 2.3
(10^6 ×magnification). (a)Single carbon atom. (b)Glucose, a simple sugar molecule. (c)ATP, a nucleotide.
(d)Chlorophyll molecule. (e)Transfer RNA, or “tRNA.” (f)Anantibody, a protein used by the immune system.
(g)The ribosome, a large protein machine. (h)The virus responsible for polio. (i)Myosin, a molecular machine
discussed in Chapter 10. (j)DNA, a nucleic acid. Chapter 9 will discuss the mechanical properties of long molecules
like this one. (k)F-actin, a cytoskeletal element. (l)Ten enzymes (protein machines) involved in glycolysis, a
series of coupled chemical reactions that produce ATP, the energy currency molecule, from glucose. Chapter 11 will
discuss ATP production. (m)Pyruvate dehydrogenase, a large enzyme complex also discussed in Chapter 11. [From
(Goodsell, 1993).] [Copyrighted figure; permission pending.]
Cells are the fundamental functional units of life. Whether alone or integrated into communities
(organisms), individual cells perform a common set of activities. More precisely, while a particular
cell may not do everything on the following list—there are a couple hundred distinct, specialized
cell types in our bodies, for example—still there is enough overlap between all cells to make it clear
that all are basically similar.
- Like entire organisms, individual cells take in chemical or solar energy. As discussed in
Chapter 1, most of this energy gets discarded as heat, but a fraction turns into useful
mechanical activity or the synthesis of other energy-storing molecules, via a set of
processes collectively called “metabolism.” Chapter 11 will examine one aspect of
this remarkably efficient free energy transduction process. - In particular, each cell manufactures more of its own internal structure, in order to
grow. Much of this structure consists of a versatile class of macromolecules called
“proteins.” Our bodies contain about 100 000 different kinds of protein. We will