BIOCHEM 2B03 Chapter Notes - Chapter 28: Eukaryotic Dna Replication, Type I Topoisomerase, Turnover Number
6 Sep 2013
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Chapter 28: dna metabolism: replication, recombination and repair. Rule identify the 5" ends and 3" ends. Rule biosynthesis of nucleic acids proceeds in the 5" to 3" direction. Dna is replicated by a nucleophilic substitution reaction: (dna)n + dntp (dna)n+1 + ppi, nucleophilic attack of 3" hydroxyl on the 5" phosphate of the incoming ntp. Dna replication is a chemical reaction: o atom in the hydroxyl is electron rich (nucleophile, p atom in the 5" phosphate is electron poor (electrophile) Inorganic pyrophosphate is displaced from the incoming dntp. Many reactions that involve the liberation of ppi are energetically unfavorable that is go" of the reactants is similar to or less than that of the products. The key is the pyrophosphate: (dna)n + dntp (dna)n+1 + ppi. The enzyme inorganic pyrophosphatase degrades ppi and the removal of this product is what causes the reaction to proceed (think le chatelier: eg/ (dna)n + dntp (dna)n+1 + ppi.
