1. DNA Replication Pt. 2 10.5 Pgs. 188 – 189 Objective: I can describe in EXCRUCIATING detail how DNA is replicated. File:/dna-replication1.swf

2. 1) DNA unwinds and unzips  Enzyme: Helicase  Single-stranded DNA stabilized  Single-Strand Binding Proteins (SSB)  Replication Fork – site where unzips  Template strand = strand that is read (a.k.a. parent strand) Replication fork

3. 2) Primer added to each template strand  Made of RNA (few hundred nucleotides)  Provides place to start adding DNA Enzyme: Primase

4. 3) Build new DNA using old as template (semi-conservative replication)  Enzyme: DNA Polymerase (III)  Starts at primer (can’t start on single-strand)  Adds matching nucleotide  Can only build 5’ to 3’ (read 3’ to 5’) Polymerase adds nucleotides to 3’ end of newly made strand

5.  Because DNA is anti-parallel (and DNA polymerase only builds 5’ to 3’)…  Leading strand: build continuously  Lagging strand: build discontinuously  Segments in lagging strand called Okazaki fragments http://highered.mheducation.com/sites/0072943696/student_view0/chapter3/animation__dna_replication__quiz_1_.html http://highered.mheducation.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120076/micro04.swf::DNA+Replication+Fork File animations

6. 4) Primers (made of RNA) removed and replaced with DNA nucleotides  Enzyme: RNase H (a.k.a. DNA polymerase I) 5) Gaps between newly constructed strands filled in – making last phosphodiester bond (because DNA Polymerase can only…)  Enzyme: DNA ligase http://www.youtube.com/watch?v=4PKjF7OumYo http://www.youtube.com/watch?v=4jtmOZaIvS0

7.  Enzymes are good at proofreading and repairing mistakes  Especially DNA Polymerase (III)  However, proofreading not perfect  This is OK, because this leads to mutation, and with mutation… Can have evolution http://highered.mheducation.com/sites/9834092339/student_view0/chapter14/proofreading_function_of_dna_polymerase.html