Cracking the AP Biology Exam


Molecular Genetics


You’ll recall from our discussion of bioenergetics in Chapter 4 that enzymes are proteins that are essential for life. This is true not only because they help liberate energy stored in chemical bonds, but also because they direct the construction of the cell. This is where DNA comes into the picture.

DNA’s main role is directing the manufacture of proteins. These proteins, in turn, regulate everything that occurs in the cell. But DNA does not directly manufacture proteins. Instead, DNA passes its information to an intermediate molecule known as ribonucleic acid (RNA). These RNA molecules carry out the instructions in DNA, producing the proteins that determine the course of life.

The flow of genetic information is therefore:

DNA → RNA → proteins

This is the central doctrine of molecular biology.

We said in the beginning of this chapter that DNA is the hereditary blueprint of the cell. By directing the manufacture of proteins, DNA serves as the cell’s blueprint. But how is DNA inherited? For the information in DNA to be passed on, it must first be copied. This copying of DNA is known as DNA replication.