All students in biology and many others have heard of the “central dogma” of molecular biology (see chap. 1, Figure 1.3). DNA is transcribed into RNA, which then is translated into proteins. This “central dogma” is memorized by countless people every year and becomes ingrained in their thoughts about all molecular biology processes. While it is a useful hook for people to remember, it is an oversimplication of what actually goes on in cells and leads to misconceptions. First of all, as you are aware, there are several different categories of RNA. There are messenger RNAs (mRNAs), ribosomal RNAs (rRNAs), transfer RNAs (tRNAs), and a diverse set of other small noncoding RNAs (ncRNAs) that function in the control of expression of the other RNAs. Where do these t into this scheme? Figure 4.1 shows an overview of this more complex process. Also, the cellular concentrations of these RNAs vary. How does this affect these processes?