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DNA Structure and Replication

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DNA Structure and Replication. I. Introduction and Review of Nucleic Acids and Genes ... III. Replication. B. Steps in DNA replication: Figure 13.4. 1. Double ... – PowerPoint PPT presentation

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Title: DNA Structure and Replication


1
  • 13
  • DNA Structure and Replication

2
  • I. Introduction and Review of Nucleic Acids and
    Genes
  • A. Genes
  • 1. HistoryKnown that chromosomes contain genetic
    information by 1920.
  • 2. Genetic studies in the 1930s and 1940s
    indicate that DNA is the genetic information.
  • 3. QuestionsHow does DNA specify a protein? How
    is it copied at each cell division?

3
  • The Watson-Crick Double Helix
  • A. Identity of Watson and Crick
  • B. Techniques they used to analyze structure of
    DNAx-ray crystallography with aid of Rosalind
    Franklin collaborating with Maurice Wilkins

4
  • The Watson-Crick Double Helix
  • Nucleotides and Nucleic Acids
  • Review three components of nucleotidesfive-carbon
    sugar, phosphate, and four types of
    nitrogen-containing bases.
  • b) Joined together in covalent bonds between
    sugar and phosphate to make a chain

5
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6
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7
  • The Watson-Crick Double Helix
  • Components of Model
  • Nucleotides
  • Nitrogen bases are laid out in specific and
    highly varied order, carrying code for protein
    synthesis.
  • (animation)

8
  • Two chains wrapped around each other like a
    spiral staircase, with the sugar-phosphate
    covalent bonds making the sides of the staircase.

9
  • Two sides of staircase are held together by
    hydrogen bonds between the N- bases (A, C, G, and
    T) like steps of the staircase.
  • Each base makes half a stair with the other
    always made up of its complement A T, and G
    C.

10
  • III. Replication
  • 2. Each of the two original strands serves as a
    template (pattern) for construction of a new
    matching strand.

11
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12
  • III. Replication
  • B. Steps in DNA replication Figure 13.4
  • 1. Double helix unwinds.
  • 2. Nucleotides on each of two single strands are
    now available to form base pairs with their
    complement from a new free-floating nucleotide.
  • 3. Both original strands can be copied, making
    two double helices from one original.
  • Animation
  • 4. The new helices are composed of half old
    (original) and half new nucleotides Figure 13

13
DNA Zipper
14
DNA Replication in Action
15
New DNA Strands are Identical
16
DNA is now copied so mitosis or meiosis can take
place.
17
  • 5. Replication is complex, but catalyzed by
    enzymes
  • a) The addition and matching of new bases is
    catalyzed by DNA polymerase.
  • b) DNA ligase permanently attaches short sections
    together to make one long chromosome.

18
  • III. Replication
  • C. Importance of error-free copying
  • 1. Error rate minimized by DNA polymerase
    proofreading.
  • 2. Bacterial polymerase brings 10 million bases
    together incorrectly, but makes only 1/100,000
    mistakes.

19
  • Mutations
  • A. Mutation permanent alteration in cells DNA
    base sequence Figure 13.6
  • 1. Point mutationsslight change in chemical form
    of base, or incorrect base pairs
  • 2. Chromosomal mutations Chapter 12
  • B. Almost all cancers begin as a mutation that is
    passed along at replication.
  • 1. In somatic cells (body cells)
  • 2. Mutation rate is low, but after decades of
    accumulated mutations, cells can become
    malignant.

20
  • C. Heritable mutations occur in germ-line cells
    (cells that divide to make sperm and eggs).
  • D. Heritable mutations also create genetic
    diversity.

21
The End
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