58 Chapter 2. What’s inside cells[[Student version, December 8, 2002]]
nuclear poresmFigure 2.31:(Schematic.) The flow of information in a cell. Sometimes the product of translation is a regulatory
protein, which interacts with the cell’s genome, creating a feedback loop. [Copyrighted figure; permission pending.]
Figure 2.32:(Drawing, based on structural data.) Transcription of DNA to messenger RNA by RNA polymerase,
awalking motor. The polymerase reads the DNA as it walks along it, synthesizing its mRNA transcript as it moves.
[From (Goodsell, 1993).] [Copyrighted figure; permission pending.]
distant from each other along the chain, or even in another chain.
5.The folded protein may then form part of the cell’s architecture. It may become a function-
ing device, for example one of the ones shown in Figure 2.33. Or it may be a regulatory
protein, helping close a feedback loop. This last option gives a mechanism orchestrating the
development of the cell (or indeed of its surrounding organism).T 2 Section 2.3.4′on page 61 mentions some modifications to the simplified scheme given above.
The big picture
Returning to the Focus Question, we see that we have a lot of work to do: The following chapters
will need to shed physical light on the key phenomenon of specificity, self-assembly, and active
transport. As mentioned throughout the chapter, specific structures and processes from this chapter
to be discussed later include flagellar propulsion, RNA folding, the material properties of bilayer
membranes and of individual DNA and protein molecules, the structure and function of hemoglobin,