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© 2012 Pearson Education, Inc. Lecture by Edward J. Zalisko PowerPoint Lectures for Campbell Biology: Concepts & Connections, Seventh Edition Reece, Taylor,

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Presentation on theme: "© 2012 Pearson Education, Inc. Lecture by Edward J. Zalisko PowerPoint Lectures for Campbell Biology: Concepts & Connections, Seventh Edition Reece, Taylor,"— Presentation transcript:

1 © 2012 Pearson Education, Inc. Lecture by Edward J. Zalisko PowerPoint Lectures for Campbell Biology: Concepts & Connections, Seventh Edition Reece, Taylor, Simon, and Dickey Chapter 10 Molecular Biology of the Gene

2 DNA REPLICATION © 2012 Pearson Education, Inc.

3 10.4 DNA replication depends on specific base pairing In their description of the structure of DNA, Watson and Crick noted that the structure of DNA suggests a possible copying mechanism. DNA replication follows a semiconservative model. –The two DNA strands separate. –Each strand is used as a pattern to produce a complementary strand, using specific base pairing. –Each new DNA helix has one old strand with one new strand. © 2012 Pearson Education, Inc. Animation: DNA Replication Overview

4 Figure 10.4A_s1 A parental molecule of DNA G C A T T A A T C G

5 Figure 10.4A_s2 A parental molecule of DNA A C G C A T T A The parental strands separate and serve as templates Free nucleotides T A T T A A T A G G G C C A T C G C

6 Figure 10.4A_s3 A parental molecule of DNA A C G C A T T A The parental strands separate and serve as templates Free nucleotides T A T T A A T A G G G C C A T C G C Two identical daughter molecules of DNA are formed A T T A C G G C

7 Replication must occur quickly. Multiple origin of replication sites are started along eukaryotic chromosomes. DNA polymerase catalyzes DNA synthesis Problems and Solutions Associated with DNA Replication © 2012 Pearson Education, Inc. Animation: Origins of Replication Parental DNA molecule Origin of replication Bubble Parental strand Daughter strand Two daughter DNA molecules

8 DNA strands are twisted around each other and must be separated Helicase Enzyme that unwraps DNA and separate H-bonds between strands Problems and Solutions Associated with DNA Replication © 2012 Pearson Education, Inc.

9 Replication must be accurate DNA polymerase can proof-read its own work Correct mistakes Problems and Solutions Associated with DNA Replication © 2012 Pearson Education, Inc.

10 DNA Polymerase can only add nucleotides to the 3 end of a pre-exiting DNA strand One-strand synthesized as a single continuous strand (leading strand) The other (lagging strand) synthesized in small fragments (Okazaki fragments) DNA Ligase connects these fragments RNA polymerase (primase) starts replication by building a small, RNA primer Problems and Solutions Associated with DNA Replication © 2012 Pearson Education, Inc.

11 5 end 3 end P P P P P HO A T C G GC P P P A T OH 5 end 3 end Remember….. DNA strands run in opposite directions. 5 indicates open P end 3 indicates open -OH end

12 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 DNA Polymerase can only attach nucleotides to 3-end

13 Overall direction of replication DNA ligase Replication fork Parental DNA DNA polymerase molecule This daughter strand is synthesized continuously This daughter strand is synthesized in pieces Animation: Lagging Strand Animation: Leading Strand

14 LE Parental DNA 5 3 Leading strand Okazaki fragments Lagging strand DNA pol III Template strand Leading strand Lagging strand DNA ligase Template strand Overall direction of replication

15 5 3 Parental DNA 3 5 Overall direction of replication DNA polymerase Replication fork Leading strand DNA ligase Primase OVERVIEW Primer DNA polymerase DNA polymerase Lagging strand Lagging strand Leading strand Leading strand Lagging strand Origin of replication Animation: DNA Replication Review

16 Bacteria cultured in medium containing 15 N DNA sample centrifuged after 20 min (after first replication) DNA sample centrifuged after 40 min (after second replication) Bacteria transferred to medium containing 14 N Less dense More dense Conservative model First replication Semiconservative model Second replication


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