Chapter6 - Each strand serves as a template for synthesis...

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Unformatted text preview: Each strand serves as a template for synthesis of the complementary strand Figure 6.1: DNA replication as originally envisaged by Watson and Crick. Meselson and Stahl proved DNA replication is semiconservative Meselson and Stahl proved DNA replication is semiconservative Figure 6.3: Results of the Meselson-Stahl Experiment. The top of the tube is at the left, the bottom at the right. Reproduced from M. Meselson and F. W. Stahl, Proc. Natl. Acad. Sci. USA 44 (1958): 671x682. Photo courtesy of Matthew Meselson, Department of Molecular and Cellular Biology, Harvard University. DNA in chromosomes is replicated semiconservatively Figure 6.5: Results of chromosome replication and labels of sister-chromatid exchange Replication of a circular DNA molecule through a structure Figure 6.7b: The parental and daughter segments Replication can be uni- or bidirectional During -form replication, both parental DNA strands remain intact. Figure 6.8: The distinction between unidirectional and bidirectional DNA replication Eukaryotes use multiple origins to replicate the chromosome Figure 6.12: How bubbles enlarge and merge in bidirectional replication Key proteins at the DNA replication fork Figure 6.13: Role of key proteins in DNA replication DNA gyrase relieves the stress of helix unwinding Figure 6.14: DNA gyrase introduces a doublestranded break ahead of the replication fork and swivels the cleaved ends around the central axis to relieve the stress of helix unwinding. The components that differ between DNA and RNA Figure 6.15: Differences between DNA and RNA DNA synthesis requires an RNA primer DNA polymerase adds dNTPs to the free 3'-OH of the RNA primer Figure 6.16: Priming of DNA synthesis with an RNA segment The RNA primer at the 5' end of new DNAs must be removed Figure 6.17: Precursor fragment structure Addition of a deoxynucleotide to the 3'-OH end of a primer chain DNA synthesis always proceeds in a 5' to 3' direction Figure 6.18: Addition of a nucleotide to the 3'-OH terminus of a primer strand The lagging strand is synthesized discontinuously Figure 6.20: Okazaki fragments in the replication fork Events in joining precursor fragments in the lagging strand Removal of the RNA primer Replacement of the primer with DNA Joining adjacent DNA fragments Joining adjacent DNA precursor fragments in eukaryotes Figure 6.22: Joining of adjacent precursor fragments in eukaryotes Dideoxynucleotides lack a 3'-OH and are chain terminators Figure 6.23: Deoxyribose and dideoxyribose Sanger sequencing takes advantage of ddNTP chain terminators Figure 6.24: Dideoxy method of DNA sequencing DNA sequencing machines use fluorescent dideoxynucleotides Figure 6.25: Trace of fluorescence pattern from a DNA sequencing gel Double-strand break repair pathways Figure 6.30: Double-strand break in a duplex DNA molecule with overhanging 3' ends facing the gap Adapted from D. K. Bishop and D. Zickler, Cell 117 (2004): 9x15. Resolution of Holliday junctions Figure 6.31: Resolution of Holliday junctions ...
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