Lecture 21Outline of Last Lecture I. Nucleic AcidsA. Nitrogenous BasesB. Base NumberingII. Base Linkages and PhosphorylationIII. Sugar Backbone of DNA and RNAIV. NucleosidesA. Nucleoside Uses in MedicineV. DNA Outline of Current Lecture I. The Central DogmaII. Semi-Conservative ReplicationIII. DNA Replication ProcessIV. Eukaryotic DNA ReplicationV. Prokaryotic DNA ReplicationCurrent LectureThis next chapter focuses on DNA replication. DNA is what holds the information needed to make an organism. It is what is transmitted from generation to generation. DNA is made into RNA, which is translated into proteins. This can all be summarized through the central dogma of DNA. DNA acts as the template to replicate itself. It is transcribed into RNA. RNA can turn into DNA through reverse transcription. RNA is the template that is translated into protein. When DNA is replicated, a single chromosome forms 2 daughter chromosomes. DNA replication is known as being semi-conservative. This means that each strand acts as a template for the new. Each daughter double helix contains one template strand. This was proven through experiments looking at multiple generations of replication.The enzyme that is “in charge” of DNA replication is called DNA polymerase. The nucleosides during replication are called dATP, dGTP, dCTP, and dTTP. These stand for deoxy-nucleoside triphosphates. DNA polymerase can only replicate DNA going in the 5’ to 3’ direction. A primer is needed to get the replication process going. The primer contains a short strand of bases that makes the hydroxyl group available. As new bases are added the phosphorylation process cause one phosphate to bond and the other two leave. Eukaryotic DNA replication occurs at replication forks. This is caused by DNA opening up and separatinginto the two strands. This leads to the formation of replication origins. The unwound DNA is now open for eachstrand to serve as a template. DNA has directionality. This causes one strand to be the leading strand. The leading strand goes from the 3’ to 5’ direction, which means the replication naturally occurs in the 5’ to 3’ direction. The other strand is facing the opposite way, due to DNA’s antiparallel properties. This template is called the lagging strand. Its replication occurs discontinuously. The leading strand is replicated continuously. BCHM 307 1nd EditionThe lagging strand requires multiple primers to keep the process going. This causes DNA to be replicated in short strands, called Okazaki fragments.Prokaryotic DNA is replicated in a different way. This is due to prokaryotic DNA being circular. The circle starts to open up in both directions at an origin. There are two replication forks and the original strands are being replicated in opposite directions simultaneously. The strands reach the terminus end and split into two newly replicated
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