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Molecular Genetics

Molecular Genetics. DNA & Replication. DNA Structure. Nucleotides - Deoxyribose sugar Phosphate Nitrogen Bases Purine/Pyramidine Pairing - Adenine/Thymine Guanine/Cytosine (Chargaff ’ s 1:1 Rule) Directionality 3′ carbon - exposed hydroxyl group 5′ carbon – exposed phosphate group.

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Molecular Genetics

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  1. Molecular Genetics DNA & Replication

  2. DNA Structure Nucleotides - Deoxyribose sugar Phosphate Nitrogen Bases Purine/Pyramidine Pairing - Adenine/Thymine Guanine/Cytosine (Chargaff’s 1:1 Rule) Directionality 3′ carbon - exposed hydroxyl group 5′ carbon – exposed phosphate group

  3. History of DNA, Ch.16 (know these for the exam): • Watson & Crick • Chargaff's rule • Franklin • Hershey & Chase • Willkins • McLeod/Avery/McCarty • Griffith

  4. Chromosome Structure

  5. Euchromatin vs. Heterochromatin

  6. Transposons • DNA segments that can move to new locations • Can encode transposon enzymes • Effect of insertion mutation: may or may not affect gene expression • In bacteria, can carry antibiotic resistance and jump between genome and plasmids • In humans, some Alu insertions linked to disease (breast cancer, hemophilia, type II diabetes) • Alu insertion in ACE gene linked to athletic performance

  7. Chromosome Structure • http://www.youtube.com/watch?v=qYsW0jIFH5A (1:17) • http://www.youtube.com/watch?v=eYrQ0EhVCYA (2:18) • http://www.youtube.com/watch?v=gbSIBhFwQ4s (1:42)

  8. DNA Replication • Semiconservative • ½ old – template strand • ½ new – complementary strand • Requires enzymes • Copy: Antiparallel 5′ → 3′ direction Leading Strand Lagging Strand

  9. Nucleotide Triphosphates supplying energy for bonding

  10. Enzymes/Proteins Helicase Unzips DNA (break H+ bonds) to form Replication Fork SSBPs (single-strand DNA-binding proteins) Maintains strand separation Topoisomerases Breaks/rejoins double helix to prevent knots Primase Initiates replication by synthesizing an RNA primer Inserts at special “origin of replication” sequences DNA Polymerase Assembles new DNA strand Unidirectional movement (reads 3′ → 5′ ) Replaces RNA primer afterwards DNA Ligase Connects Okazaki fragments (short segments on lagging strand)

  11. Replication Fork

  12. Okazaki fragments

  13. DNA Replication Animations http://www.youtube.com/watch?v=-mtLXpgjHL0 (2:04) http://www.youtube.com/watch?v=I9ArIJWYZHI (2:18)

  14. Telomeres The ends of eukaryotic (linear) chromosomes Repeating nucleotides (vertebrates: TTAGGG x 1000+) Lagging strand has no primer at one end, leaving a single-stranded section of template that will be degraded (shortening the chromosome) Telomerase adds more repeating bases to the lagging strand Prevents the lagging strand from getting shorter with each replication Absent in somatic cells: chromosomes get progressively shorter over time, limiting lifespan of tissue Secret to immortality? Cancer cells express telomerase

  15. Telomerase Animations http://www.youtube.com/watch?v=AJNoTmWsE0s (2:06) http://www.youtube.com/watch?v=DV3XjqW_xgU (4:38) *if time

  16. Repairing Mistakes DNA Polymerase proofreads and corrects mismatched bases (1/100K times) Acts as an exonuclease (cleaves bonds), reducing the error rate to about 1  10–7 Mismatch Repair Enzymes Redo section missed by DNA Polymerase Nucleotide Excision Repair System Fix DNA damaged by mutagens (ex: UV rays)

  17. Nucleotide Excision Repair http://www.youtube.com/watch?v=uN82GLQYAUQ (1:05) http://www.youtube.com/watch?v=CcTayxEblio (0:42) http://www.youtube.com/watch?v=bgUH9NfO2QM (0:27)

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