lecture08 - Biology 172 Lecture 8: Monday, May 24, 2010...

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1 Lecture 8: Monday, May 24, 2010 Biology 172 Today’s Outline Announcements Models for DNA Replication - Conservative model - Semi-conservative model - Dispersive model - Meselson-Stahl Expt DNA Replication - Basic Features - Initiation - Elongation - Termination DNA Repair •  Discussion Tomorrow: Herbicides Quiz on Photosynthesis
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2 What does DNA do? 1. Copy Function - Faithfully copied during cell division DNA Replication 2. Expression Function - Encodes cellular products that determine phenotype RNA Protein Transcription Translation
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3 Structure of DNA
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4 Models for DNA Replication Semi-conservative model Conservative model Dispersive model
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5 Fig14.8 The Meselson-Stahl experiment
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6 Fig14.8 The Meselson-Stahl experiment Semi-conservative model - consistent with all data Conservative - eliminated after 1st generation Dispersive - eliminated after 2nd generation
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7 Figure 4-9 DNA FORMS A TEMPLATE FOR ITS OWN SYNTHESIS. 1. If the hydrogen bonds between complementary base pairs are broken, the DNA helix can separate. 2. Each strand of DNA can serve as a template for the formation of a new strand. Free nucleotides attach according to complementary base pairing. 3. When the new strands polymerize to form a sugar- phosphate backbone, secondary structure is restored. New New Old Old Conclusion: The original molecule has been copied. Each copy has one strand from the original DNA molecule and one new strand.
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8 Today’s Outline Chromosome Structure Models for DNA Replication - Conservative model - Semi-conservative model - Dispersive model - Meselson-Stahl Expt DNA Replication - Basic Features - Initiation - Elongation - Termination DNA Repair
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9 New strand 5 end Phosphate Base Sugar Template strand 3 end 5 end 3 end 5 end 3 end 5 end 3 end Nucleoside triphosphate DNA polymerase Pyrophosphate - new nucleotides are added to an existing chain by phosphodiester bonds - catalyzed by DNA polymerase - requires a template - requires dNTPs - proceeds in the 5’ to 3’ direction Basic Features of DNA Replication
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10
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11 DNA Synthesis Proceeds in Two Directions A chromosome being replicated
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12 DNA Synthesis Proceeds in Two Directions Bacterial chromosomes have a single point of origin. New DNA Old DNA Origin of replication Replication proceeds in both directions 5 5 3 3 Fig. 14.10
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13 DNA Synthesis Proceeds in Two Directions Replication bubble Old DNA Eukaryotic chromosomes have multiple points of origin. Replication fork New DNA Replication proceeds in both directions from each starting point 3 3 5 5 5 5 3 3 3 3 5 5 Fig. 14.10
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Topoisomerase relieves twisting forces Helicase opens double helix 3 5 5 A is opened, unwound, and primed. 5
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lecture08 - Biology 172 Lecture 8: Monday, May 24, 2010...

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