DNA Replication, Mutations, and Repair

Abstract

Replication (i.e. copying) of DNA takes place before cell division. During replication one double-stranded DNA molecule produces two identical copies. Each strand of the original double-stranded DNA molecule serves as a template for the production of the complementary strand, a process referred to as semiconservative replication. Replication is triggered by a transcription factor, in yeast called MCB binding factor, in mammals — E2F, that regulates the expression of enzymes necessary for replication: DNA polymerases, DNA primases and cyclins. Replication starts in a specific place (called replication origin) (Fig. 4.1). In genomic DNA of E. coli there is only one place of replication origin (called oriC), whereas eukaryotic DNA has many such sites on each chromosome. In a sequence of replication origin, A:T pairs dominate, which are easier to separate than a C:G pairs, because they are connected only by two hydrogen bonds. Unwinding of DNA at the origin and synthesis of new strands leads to the formation of a replication fork (Fig. 4.2).