1/18/2016 Replication requires: Some Enzymes Involved in DNA 1 Uncoiling the parent DNA Replication and Their Functions 2.Unzipping the hydrogen bonds between base pairs exposing the nucleotide sequence of each strand to serve as a Enzyme Function template Helicase Unzipping the DNA helix 3.Synthesizing two new strands by attaching complementary Primase Synthesizing an RNA primer nucleotides to each single-strand template DNA polymerase IIl Adding bases to the new DNA chain;proofreading the chain for mistakes Ligase Final binding of nicks in DNA during synthesis and repair Gyrase Supercoiling Details of DNA Replication Details of DNA Replication Begins at an origin of replication:a short AT rich sequence DNA polymerase III adds nucleotides in a 5'to 3'direction Helicase unwinds and unzips the DNA double helix; leading strand-synthesized continuously in 5to 3 breaks hydrogen bonds direction ection is 3'to 5 G 51/18/2016 5 Replication requires: 1. Uncoiling the parent DNA 2. Unzipping the hydrogen bonds between base pairs exposing the nucleotide sequence of each strand to serve as a template 3. S nthesizin t ne str nds b tt chin Synthesizing two new strands by attaching c mplement r complementary nucleotides to each single-strand template DNA Polymerase Helicase Template strands 1 2 3 3 • Begins at an origin of replication: a short AT rich sequence • Helicase unwinds and unzips the DNA double helix; Details of DNA Replication p ; breaks hydrogen bonds • An RNA primer is synthesized by primase, an RNA polymerase • DNA polymerase III adds nucleotides in a 5′ to 3′ direction leading strand – synthesized continuously in 5′ to 3′ Details of DNA Replication leading strand synthesized continuously in 5 direction lagging strand – synthesized 5′ to 3′ in short segments; overall direction is 3′ to 5′