6.2 Replication

• Replication is the process in which genetic information is passed on to the next generation
• In eukaryotes, replication takes place in the nucleus of the cell
• In prokaryotes, replication occurs in the cytoplasm since they do not have a nucleus
• Replication is a multi-step process that involves multiple enzymes
• DNA Replication
• The first step in DNA replication is to unwind and break the hydrogen bonds in the twisted DNA
• Helicase unwinds the DNA strands and breaks the hydrogen bonds between the bases
• Topoisomerase and single-strand binding proteins relax the coil in front of the replication fork and prevent recoiling
• DNA polymerase III adds corresponding nucleotides to the template strand after RNA primase adds an RNA primer
• DNA polymerase I goes through the replicated DNA to fix mistakes and replace the RNA primer with DNA nucleotides
• Ligase glues the newly replicated segment that used to be the RNA primer with the rest of the DNA strand
• Leading and Lagging Strand
• DNA replication is a "semiconservative" process, conserving one unchanged DNA strand to serve as a template
• DNA polymerase III works in the 5' → 3' direction on the leading strand
• The lagging strand is replicated in small segments called Okazaki fragments
• Ligase glues all the Okazaki fragments together to complete the lagging strand replication
• DNA polymerase III needs space to bind to the template strand, leading to the loss of a few base pairs during replication
• Telomeres are bits of unimportant DNA added at the end to compensate for the loss of base pairs
• Loss of DNA due to inefficient replication can lead to the body malfunctioning
• Conclusion
• DNA replication involves unwinding DNA and using the existing strand as a template
• Helicase acts as "scissors" by cutting DNA through breaking hydrogen bonds
• Topoisomerase and single-strand binding proteins prevent DNA from recoiling
• DNA polymerase I edits mistakes and replaces the RNA primer with DNA nucleotides
• Ligase functions as the glue in DNA replication
• DNA polymerase III works only in the 5' → 3' direction, leading to the replication of the lagging strand in Okazaki fragments