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DNA Structure and Replication

DNA Structure and Replication. Lifespan Gene In The News. Chromosomes . Contain all information for an organism Karyotype = arrangement of chromosomes. Eukaryotic Chromosomes. Chromatin = DNA Histone proteins condenses to form strands called chromosomes,

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DNA Structure and Replication

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  1. DNA Structure and Replication

  2. Lifespan GeneIn The News

  3. Chromosomes • Contain all information for an organism • Karyotype = arrangement of chromosomes

  4. Eukaryotic Chromosomes • Chromatin = • DNA • Histone proteins • condenses to form strands called chromosomes, • Strands occur just prior and during cell division

  5. DNA • Double stranded, coiled molecule

  6. Discovery of Hereditary Material • Friedrich Miescher (1869) • Isolates “nuclein” from nucleus • was not called DNA until the 1920’s • No notion it contained hereditary material • Gregor Mendel (late 1800s) • Pioneering work in genetics • Traits are inherited discrete factors

  7. Discovery of Hereditary Material • Walter Sutton (early 1900s) • Suggested chromosomes held hereditary factors • No direct evidence for support • Thomas Hunt Morgan (1910) • Provided experimental evidence to support Sutton • Identified X (sex) hormone • worked with chromosomes of fruit flies and eye color

  8. Discovery of Hereditary Material • Phoebus Levene (1920s) • Two types of nucleic acid in cells, composed of repeating nucleotides • Both types with nearly identical structures • DNA & RNA are the 2 types

  9. Nucleotide Structure • Three different components • Phosphate group • Nitrogen containing base (A,T,G,C,U) • Five-carbon sugar (ribose or deoxyribose)

  10. Nitrogen Containing Bases

  11. Discovery of Hereditary Material • Oswald Avery (early 1940s) • Preliminary evidence for DNA as hereditary material • Transformed bacteria by transferring DNA

  12. Discovery of Hereditary Material • Edwin Chargaff (late 1940s) • Proportion of bases varies in the DNA of different type organisms • Portions of bases roughly equal, (A=T & C =G) • Purines = pyrimidines (A + G = C + T)

  13. Discovery of Hereditary Material • George Beadle & Edward Tatum (1950s) • One-gene-one-enzyme theory • Enzyme production under control of genes • Alfred Hershey & Martha Chase (1952) • Building of Avery’s work, confirmed DNA as hereditary material

  14. Discovery of Hereditary Material • Rosalind Franklin & Maurice Wilkins (1953) • Developed double helix model for DNA • Evidence from X-ray diffraction

  15. Discovery of Hereditary Material • James Watson & Francis Crick (1953) • Structure of DNA • Synthesized previous research • Nobel Prize in 1962, along with Wilkins, Franklin died before nominations were made

  16. Structure of DNA

  17. Discovery of Genetic Code

  18. DNA is Self-Replicating • Before Cells divide • Enzymes break bonds between bases • Complementary strands separate • Complementary bases are added to strands • Copy of DNA results

  19. Replication Mechanisms • Replication begins at various points • Proceeds in both directions

  20. Replication Mechanisms • DNA molecule separates at its bases • Forms split, or replication fork • Each strand acts as a template

  21. Replication Mechanisms • Replication proceeds from 5‘ to 3‘ end

  22. Genes • One-gene-one-enzyme theory • Production of a given enzyme is under control of a specific gene • Production of a given peptide is under control of a single gene (revised statement)

  23. Gene • The unit of heredity • Is a sequence of nucleotides • Codes for amino acid sequences of polypeptides or for RNA

  24. DNA Sequences • Genome = all genetic information • Promoters = “start here” part of sequence • Introns = extra sequences between polypeptide-specifying portions, are not expressed, interrupt most eukaryotic genes • Exons = portions of a gene that are expressed

  25. Repeated Sequences • Repetitive DNA • 20-50% of eukaryotic DNA • May play structural roles in chromosomes

  26. Repeated Sequences • Telomeres • At ends of chromosomes • Shorten as cell replicates • Cells do not function when telomeres become too short Telomeres in yellow

  27. Mutations • Change can occur in DNA • Point mutation or gene mutation • Change in genetic message • Chromosome mutation

  28. Sources of Mutation • Ionizing radiation • Ultraviolet radiation • Some chemicals • Transposable elements

  29. Transposable Elements • “jumping genes” • Some DNA sequences move from one position to another • Make up more than 40% of human genome • First reported by Barbara McClintock

  30. Transposable Elements • Significance • Contribute to rate of mutation • May cause visible changes • Example: mottling in corn

  31. End Chapter 9

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