Lecture.12.Fall.2013

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Unformatted text preview: yrase vs. topoisomerase DNA gyrase is specific to prokaryotes - eukaryotic cells don’t encode gyrase Instead, eukaryotic cells use topoisomerases - what do these enzymes do? unwind as well DNA gyrase is a popular target for antibiotics - why? replication would not continue if there was no gyrase human cells dont have gyrase, thus it wont harm you. Initiation, continued: Primers • DNA polymerases cannot initiate DNA synthesis on a base template • They require a primer, providing an existing 3’OH group to which a new nucleotide can be added. • To solve this problem, an enzyme called primase synthesizes short (~10-12 nt) strands of RNA nucleotides to get replication started. rna can sythesize outta nowhere • These are called primers. Primers • Primase is an RNA polymerase (not DNA) and does not require a 3’-OH group to which nucleotides can be added. can start from scratch • On the leading strand, how many primers do you require? • On the lagging strand, how many primers do you require? 1 a lot Primase synthesizes short RNA primers, providing a 3’-OH 3. Elongation: DNA polymerases • DNA polymerase III is a larg...
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This document was uploaded on 02/25/2014.

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