De Novo Replication - Lecture notes 1-3 PDF

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De novo replication molecular biology notes...

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DE NOVO REPLICATION o OriC (Chromosomal origin of replication) is about 250 bp long o It contains recognition sites for DNA binding proteins: Dna A and ATP  This binding causes the denaturation of A+T rich sections of the ori and opens a bubble  Unwinding in both directions is accomplished by helicase  ssb single-stranded DNA binding proteins bind to the single strands and keep them from re-annealing  RNA Primers are made:  RNA polymerase on the leading strand  RNA primase on the lagging strand  DNA polymerase III extends the primer as DNA  The polymerases: o Polymerase I and II can be largely thought of as repair enzymes o Polymerase III is the major replication enzyme  Require a template  Require dNTP s  Require a primer which provides a free 3 -OH group to hook the next nucleotide onto  Look over fig 7-11 to see the significance of a primer  Note that synthesis occurs 5  3 (fig 7-12)  Both pol I and pol III have proofreading ability  Called 3  5 exonuclease activity  If wrong base inserted, i.e., no base-pairing after synthesis, the pol goes backwards and chews out the mis-matched base and tries again. (See fig 7-13)  pol I only: has 5  3 exonuclease activity: It can chew up any DNA that it bumps into AS it is synthesizing new DNA.  This is important in a technique known as nicktranslation (See fig. 7-14).  Compare the differences between pol I and pol III in table 7-1, page 131.  The Mechanics of Replication o Study figure 7-15 and note that this scheme is impossible because:  All the known DNA replicating enzymes use the 3 -OH group as the growing end. (The 5 -PO4 end does not grow or elongate!)...