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Lecture 30 Replic_Repair notes

Lecture 30 Replic_Repair notes - Lecture 30 DNA Replication...

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Lecture 30 DNA Replication and Repair Campbell 6 th Ed pp. 293-301 7 th Ed. pp. 299-307 I'll give a basic outline of DNA replication first, and then go through it in detail. Here's the model (Fig 16.7/16.9). First, complementary strands of DNA temporarily separate. New nucleotides are inserted in turn, following base-pairing rules. Finally, nucleotides are connected to make a new sugar- phosphate backbone. The term used for this form of replication is semi- conservative. Each new molecule contains 1 old strand and 1 new strand. The experiment done by Meselson and Stahl in the late 1950's to prove this model is explained in the text. (It won't be on the test, but it's interesting to read through). Detailed Description of DNA Replication Replication starts at specific sites called Origins of Replication. (See Fig. 16.10/16.12). Note that these don’t correspond to any particular genes or other coding information on the strands. They’re chosen mostly because they’re roughly uniform distances apart from each other. Proteins attach here and separate the strands. There are many origins of replication on each chromosome, and replication proceeds in both directions, on both strands, from each one. The areas where the two strands are separated and replication is occurring are called Replication Bubbles. Each Replication Bubble has 2 Replication Forks, one at each end, where nucleotides are actually inserted. The bubbles enlarge as replication proceeds. Deoxyribonucleoside triphosphates are the basic building blocks of DNA. They can be abbreviated dNTPs, and are present at high concentration in cells that need to replicate DNA. There are 4 kinds, each containing 1 of the 4 bases. The correct dNTP first base-pairs with the appropriate base on the template strand. Because each of the 2 separated strands of the original DNA molecule are replicated, each serves as a template for synthesis of a new strand (Fig. 16.11/16.13). The phosphate group linked to the sugar on the incoming dNTP is then linked to an -OH group on the last sugar of the new strand. Pyrophosphate, a compound consisting of 2 phosphate groups, is cleaved from the dNTP and released. Cleavage of the high-energy bond between the pyrophosphate group and the phosphate that is incorporated into the growing chain provides the energy required to form the phosphodiester bond between the phosphate and the -OH group in the chain.
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DNA synthesis is performed by an enzyme called DNA polymerase . This enzyme has two specific functions in DNA replication. First, it selects the correct dNTP, using base-pairing rules. Second, it incorporates the dNTP into the growing chain by catalyzing formation of a new phosphodiester bond.
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Lecture 30 Replic_Repair notes - Lecture 30 DNA Replication...

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