Chapter 7DNA ReplicationThe next unit involves understanding the details of how the first half ofthe Central Dogma of molecular biology works. The central dogma ofmolecular biology describes the two-step process, transcription andtranslation, by which the information in genes flows into proteins: DNA→RNA→protein (Figure 1).In this study guide, we will focus on how DNA isreplicated.Semiconservative replication — parent strands of DNA separate, serveastemplates,andproduceDNAmoleculesthathaveonestrandofparental DNA and one strand of newDNA. (Figure 2). The process of semiconservative replication occurs in threemain stages:unwinding,base pairingandjoining.UnwindingDNAhelicase,anenzyme,isresponsible for unwinding and unzippingthe double helix. When the double helix isunzipped, the hydrogen bonds betweenFigure 1: Central Dogma of Molecular BiologyFigure 2: Semi-conservative model of replication
the bases are broken, leaving each strands of DNA. Then, proteins calledsingle-stranded binding proteins associate with the DNA to keep the strandsseparate during replication. As the helix unwinds, another enzyme, RNAprimase, adds a short segment of RNA, called an RNA primer, on each DNAstrand.Base pairingThe enzyme DNA polymerase catalyzes the addition of appropriatenucleotides to the new DNA strands. The nucleotides are added to the 3’ endof the new strand. DNA polymerase continues adding to the 3’ end of the newDNA strand. Recall that each base binds only to its complement –A binds toT, and C binds to G. in this way, the templates allow identical copies of theoriginal double-stranded DNA to be produced.