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Chapter 13

Chapter 13. DNA Structure and Function. Discovering dna. Methods of inheritance uncertain Suspected that it was due to proteins (great variety) Some evidence of DNA as passing on genes in viruses 1953—James Watson, Francis Crick Described DNA model for inheritance. Building dna.

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Chapter 13

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  1. Chapter 13 DNA Structure and Function

  2. Discovering dna • Methods of inheritance uncertain • Suspected that it was due to proteins (great variety) • Some evidence of DNA as passing on genes in viruses • 1953—James Watson, Francis Crick • Described DNA model for inheritance

  3. Building dna • Deoxyribonucleic acid (DNA) • Nucleotide—monomer unit of nucleic acid • 5-carbon sugar (ribose or deoxyribose) • Nitrogen base • Phosphate group

  4. nucleotides • Adenine • Guanine • Thymine • Cytosine

  5. nucleotides • ALWAYS match with specific base pairing • A—T, T—A • G—C, C—G • Each chain bonded covalently • Base pairs bonded with hydrogen bonds

  6. Dna structure • Polarity of molecules determine shape • Double helix

  7. Dna replication • Interphase—S phase • Makes one copy, doubles amount of DNA • Semiconservative replication—in each copy, one strand of the helix is carried over from the original strand

  8. Dna replication--steps • Step 1—helicase attaches to DNA • Step 2—helicase “unzips” hydrogen bonds between base pairs • This causes double helix to “unwind”

  9. DNA replication--steps • Step 3—DNA polymerase forms new, complementary strand of DNA from free nucleotides • Moves along entire length of DNA

  10. DNA Replication--Steps • Step 3b—DNA ligase binds short stretches of new DNA on “lagging” strand • Okazaki fragments—short sequences of DNA on lagging strand

  11. DNA Replication--steps • Step 4—helicase separates from DNA • Two new strands now formed • Sister chromatids!!!

  12. Animations! • Brief Replication Overview • Brief DNA Replication • Detailed DNA Replication

  13. Dna proofreading • Rare, but sometimes mismatched base pairs • DNA polymerase usually catches these & corrects • If can’t correct mismatch, protective mechanisms stop cell division (Ch. 9, slide 19) • Repair enzymes can repair some damage • Can “snip” out damage or mismatch

  14. cloning

  15. cloning

  16. cloning • Isolate DNA from one organism • Create another organism from DNA • Second organism genetically identical to original

  17. cloning • Embryo cloning • Fertilized egg separates early in division • Natural = identical twins

  18. Cloning • Adult cloning • 1—Start with somatic cell of organism • 2—Remove nucleus of the cell • 3—Take mature egg from female • 4—Remove nucleus from egg • 5—Implant donor nucleus into egg (fused by shock) • 6—New cell begins to divide to early embryo • 7—Implant embryo into surrogate mother • 8—If goes to full term, clone is born

  19. cloning

  20. Cloning • Theraputic cloning • Somatic cell DNA into stem cell • Stem cell is undifferentiated, can turn into almost any tissue • Potentially regenerate organs

  21. cloning • Applications • Livestock • Pets • Humans??? • Organs

  22. cloning • Risks • Egg doesn’t always accept new DNA • New DNA isn’t always used properly • Ethical issues

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