Cracking the AP Biology Exam


Molecular Genetics


All living things possess an astonishing degree of organization. From the simplest single-celled organism to the largest mammal, millions of reactions and events must be coordinated precisely for life to exist. This coordination is directed from the nucleus of the cell, by deoxyribonucleic acid, or DNA.

DNA is the hereditary blueprint of the cell.

The DNA of a cell is contained in structures called chromosomes. The chromosomes consist of DNA wrapped around proteins called histones. When the genetic material is in a loose form in the nucleus it is called euchromatin, and its genes are active, or available for transcription. When the genetic material is fully condensed into coils it is called heterochromatin, and its genes are generally inactive. Situated in the nucleus, chromosomes direct and control all the processes necessary for life, including passing themselves and their information on to future generations. In this chapter, we’ll look at precisely how they accomplish this.