The Genome in Eukaryotes and its Function
Genetic information of prokaryotes and eukaryotes differ in more than their length. In prokaryotes the deoxyribonucleic acid (DNA) molecule appears as a closed loop, tightly folded to fit inside the bacterial cell. In eukaryotes the DNA is complexed with nuclear proteins and creates a specific cell organ—the nucleus—separated from the cytoplasm by the nuclear membrane. The elementary fiber of linked nucleosomes is coiled in chromatin fibers in the form of a solenoid with the DNA outside, 36 nm in diameter, which may be visualized in the electron microscope. Nuclear proteins can be divided into two main groups: histone and nonhistone proteins. Contrary to the histones which represent a narrow, well-defined group of basic proteins, the nonhistone chromatin proteins represent a highly variable group of acidic proteins of various functions. The main task after discovery of DNA as the genetic material was to elucidate in which way DNA codes biosynthesis of proteins.