DNA Replication and Transcription

Abstract

Genetic information of organisms is kept in DNA in the form of an array of nucleotide sequences, and the cell must precisely replicate its chromosomal DNA. The self-complementary nature of the double-stranded DNA molecule is the basis for accurate replication, and organisms are equipped with DNA polymerase enzyme, which adds deoxyribonucleotides to preexisting DNA chains in the 5′  3′ direction, along the template strand of DNA. One strand (the leading strand) is synthesized continuously while the other (the lagging strand) is synthesized discontinuously and is then sealed.

To extract information from DNA, a limited region of the DNA, which constitutes the gene or the gene cluster (operon), is transcribed into RNA. This process is catalyzed by RNA polymerase. As is the case with DNA polymerase, this enzyme is composed of multiple subunits and catalyzes the addition of ribonucleotides to the growing RNA chain in the 5′  3′ direction, along the template DNA. Both the startpoint and the frequency of transcription are determined by the promoter, a specific sequence of DNA to which RNA polymerase and transcription regulatory proteins can bind.