DNA Clones and Suitcases

Last week in AP Biology we talked about DNA’s history this week we talked about how those discoveries would inspire future experiments. Once Watson and Crick discovered DNA’s structure the next question is, how does it replicate?

                DNA starts to separate at the origin of replication because of helicase. It then starts to create a replication bubble and fork. Next, single stranded proteins are added to the two parental strands to prevent them from reattaching. DNA polymerase III then starts to add nucleotides to the DNA. The polymerase adds the nucleotides in the direction of 5’ to 3’. Also, there is a leading strand and lagging strand during the replication process. The leading strand is replicated continuously, but the lagging strand is replicated in Okazaki fragments. Pieces of RNA mark the beginnings of the Okazaki fragments. Once pol III is done adding nucleotides pol I start to remove the RNA pieces and replacing them with pieces of DNA. DNA ligase then finishes it all up by connecting all the DNA fragments.

                Next we learned about how the DNA is packaged. In a mixture of DNA and histones we get nucleosomes which are looped in giant supercoils that created chromosomes. The histones have the ability to switch genes on and off and when the DNA spreads out it can be accessible for transcription.