7.1Transmission and Expression of Genetic Information

As a carrier of genetic information, DNA functions as the blueprint that determines the structure and function of living organisms.

Genetic information plays two roles. The first is the role of heredity in which genetic information is transmitted from the parent to progeny. This can be transmitted from cell to cell in unicellular organisms. Although this is actually transmission from individual to individual in multicellular organisms, genetic information is basically transmitted from cell to cell because it is transmitted through germ cells. Replication of genetic information occurs prior to cell division. In particular, the DNA molecule is doubled. In this chapter, we examine that mechanism.

The other role of genetic information is to achieve the structure and function of cells and individuals using this blueprint. While proteins are the major macromolecules responsible for the structure and function, genetic information carry the information regarding what form and quantity of protein as well as in which cell and under what type of environment will the protein be produced. It carries the information that determines the location to which the produced protein will be transported, and it also determines the degradation rate of the protein. As a result, the respective cells and the individual as an aggregate of these cells can fulfill their function by forming and maintaining themselves. This phenomenon is termed gene expression. The mechanism of expression of information in DNA will be explained in Chapters 810. Traditionally, it has been assumed that basic genetic mechanisms differ between prokaryotes and eukaryotes, including structure, replication, transcription, and translation. However, when living organisms are divided into three domains, the high degree of commonality between eukaryotes and archaea and the substantial differences between these two groups and bacteria become evident (Table 7-1).

Table 7-1 The differences of organisms, belonging to three domains

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