Replication notes

3) Steps of DNA replication- all DNA has the same properties but replication is different
oriC: where DNA replication starts on bacterial chromosome.
 list item
DnaA (an enzyme) binds to bases at oriC on bact. Chromosome
 Helicase (another enzyme) binds to Dna A-oriC complex
 Helicase starts unwinding DNA at oriC, starts “unzipping” DNA strands
 Single strand binding protein attaches to unzipped DNA at “replication bubble”
 DNA polymerase: attaches to DNA primer (small swatch of DNA, complimentary to few bases that helps start DNA replication)
• Primers degrade quickly. Humans lose DNA because linear, bacteria are circular so they do not
o Note- DNA polymerase only work in a 5 prime to 3 prime direction
o Note: Helicase moves ahead of DNA polymerase, unwinding and unzipping DNA as it goes. This moves the replication bubble along
 One strand synthesized continuously (one long strand with no breaks). Other strand is synthesized discontinuously meaning that it takes little breaks.
• Strand which synthesizes continuously is called the leading strand.
• Other strand is called the lagging strand ( synthesized discontinuously) Okazaki fragments are the little bits of DNA which result from taking breaks
• Okazaki Fragments have to be patched together by DNA ligase
• DNA polymerase falls off chromosome at terminus site
 Because bacterial chromosomes are circular, after replication chromosomes are interlocked.
• So topoisomerase 4 will break both strand son one of the chromosomes, un-interlock them and then patch the chromosome back together.
 Last step! Methyl groups added to some bases in DNA =methylation
