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Transcript
Section 12.2 Replication of DNA Objectives • • Summarize the role of the enzymes involved in the replication of DNA. Explain how leading and lagging strand are synthesized differently. Main Idea • DNA replicates by making a strand that is complementary to each original strand. Semiconservative Replication • In the Watson-Crick model ◦ a replication method was suggested ◦ called semiconservative replication ◦ • In semiconservative replication ◦ DNA strands separate serve as templates produce DNA that has □ one strand of parental DNA □ one strand of new DNA • Unwinding ◦ responsibility of an enzyme DNA helicase ◦ • Unzipping ◦ breaking the hydrogen bonds between the base pairs leaving single strands of DNA ◦ • occurs at a structure called the replication fork □ location where the strands separate one strand is called the leading strand other strand is called the lagging strand Base pairing ◦ DNA polymerase catalyzes the addition of complementary nucleotides to the DNA strands • remember • A to T and C to G • Base pairing ◦ on the lagging strand nucleotides are added away fm the rep fork ◦ nucleotides are added discontinually in small segments • called Okazaki fragments • the leading strand • adds nucleotides to its end in the opposite direction Base pairing ◦ on the lagging strand the Okazaki fragment are joined by □ DNA ligase Comparing Replication with Eukaryotes and Prokaryotes • Eukaryotic DNA ◦ unwinds in multiple places as the DNA is replicated ◦ these replication sites look like bubbles along the DNA strand • Prokaryotic DNA ◦ is circular ◦ it unwinds at a single spot ◦ replication occurs in both directions until it meets