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Published byDwayne Carr Modified over 8 years ago
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DNA Structure and Function
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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
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Deoxyribonucleic acid (DNA) Nucleotide—monomer unit of nucleic acid 5-carbon sugar (ribose or deoxyribose) Nitrogen base Phosphate group
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Adenine Guanine Thymine Cytosine
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ALWAYS match with specific base pairing A—T, T—A G—C, C—G Each chain bonded covalently Base pairs bonded with hydrogen bonds
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Polarity of molecules determine shape Double helix
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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
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Step 1—helicase attaches to DNA Step 2—helicase “unzips” hydrogen bonds between base pairs This causes double helix to “unwind”
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Step 3—DNA polymerase forms new, complementary strand of DNA from free nucleotides Moves along entire length of DNA
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Step 3b—DNA ligase binds short stretches of new DNA on “lagging” strand Okazaki fragments—short sequences of DNA on lagging strand
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Step 4—helicase separates from DNA Two new strands now formed Sister chromatids!!!
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Brief Replication Overview Brief Replication Overview Brief DNA Replication Brief DNA Replication Detailed DNA Replication Detailed DNA Replication
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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
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Isolate DNA from one organism Create another organism from DNA Second organism genetically identical to original
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Embryo cloning Fertilized egg separates early in division Natural = identical twins
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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
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Theraputic cloning Somatic cell DNA into stem cell Stem cell is undifferentiated, can turn into almost any tissue Potentially regenerate organs
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Applications Livestock Pets Humans??? Organs
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Risks Egg doesn’t always accept new DNA New DNA isn’t always used properly Ethical issues
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