ap biology molecular genetics unit chapters 16 & 17

Download AP Biology Molecular Genetics Unit Chapters 16 & 17

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  • AP Biology Molecular Genetics Unit Chapters 16 & 17
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  • Chapter 16 Objectives 1.Explain how Griffith and Averys experiment with pneumococcus bacteria contributed to the understanding of molecular genetics. 2.Define transformation. Use Griffith & Avery's results to explain how it occurs. 3.Using Hershey & Chase's procedure, use given hypotheses to predict results. Evaluate each hypothesis based upon the actual results of the experiments. 4.Identify the component parts of nucleic acids. Describe their organization into DNA and RNA. 5.Explain how Chargaff's rule supports the base pairing rule. 6.Explain how the two strands of a DNA molecule are complementary. 7.Explain how DNA replication is semiconservative. 8.Outline the process of DNA replication. Include the names and roles of any enzymes involved in the process. 9.Explain why one strand of DNA is replicated continuously, while the other strand is discontinuous. 10.Define Telomere. Explain why the mechanism of replication results in the shortening of telomeres. 11.Explain how DNA condenses into chromosomes in eukaryotic cells.
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  • What part of the cell controls heredity? Actual traits are not inherited. Traits are developed. Inheritance must come from something that is in the gametes and in the resulting zygote Since the gametes and zygote are cells, the control center of heredity must have some cellular origin Cells have 3 fundamental regions Cell membrane Cytoplasm Nucleus One of these 3 regions must control heredity & determine how traits will develop in the organism
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  • What part of the cell controls heredity? It follows logically that hereditary control is centered either in the membrane, the cytoplasm, or the nucleus. We will assume two alternative hypotheses: 1.The nucleus controls heredity 2.The cytoplasm controls heredity An experiment to test these must allow for simple manipulation of cell parts and simple observation of developing traits Manipulating cell parts would be simplified by using a single celled organism, but it must be large enough to work with and observe easily, and must have some distinct inherited trait.
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  • 1943 - Hammerlings Experiment The giant unicellular algae of the genus Acetabularia are an ideal experimental subject. They are large, easy to manipulate, and easy to observe
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  • Hammerlings Experiment All Acetabularia species have a base (which contains the nucleus), a stalk, and a cap. The base and stalk are similar between species, but the cap varies greatly
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  • Hammerlings Experiment A. mediterranea has an umbrella shaped cap. A. crenulata has a crenulated (fringed) cap. If you cut off the cap, it will regenerate. The regeneration is under hereditary control
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  • Experimental Design: Cut off the cap of each alga Remove a section of the stalk (which contains cytoplasm, but not the nucleus) Place a stalk from A. crenulata on a base (containing a nucleus) of A. mediterannea (Experiment 1) Place a stalk from A. mediterannea on a base of A. crenulata (Experiment 2) Observe the regeneration of the cap on each hybrid alga
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  • Exp. #1 Stalk C on Base M If the cytoplasm controls heredity... The cap that regenerates will follow instructions from the cytoplasm in the stalk. The cap should resemble type C If the nucleus controls heredity... The cap that regenerates will follow instructions from the nucleus in the base The cap should resemble type M
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  • Exp. #1 Stalk C on Base M The algae regenerated type M caps, suggesting the nucleus in the base of the cell controlled the development of the cap
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  • Exp. #2 Stalk M on Base C Similarly, algae with a nucleus from type C regenerated a crenulated cap. In both experiments, the nucleus controlled regeneration
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  • The Nucleus as Control Center If the nucleus is the center of hereditary control, there must be something inside of it that actually directs the development of traits. The nucleus consists almost entirely of: Proteins Nucleic Acids DNA RNA
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  • What material in the nucleus controls heredity? Nucleic Acids? DNA and RNA Complex polymer made of nucleotides Nitrogenous bases are variable 4 types (AGCT) Protein? Complex polymer made of amino acids Amino acid side chains are variable 20 different types of essential amino acids commonly found in protein With more variability, protein was the favored hypothesis
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  • What material in the nucleus controls heredity? To test these hypotheses, we need to separate the proteins from the nucleic acids, treat a test subject with each, and observe the results. Viruses are made entirely out of nucleic acids and proteins. Viruses inject their genetic material into a host cell, take over the hereditary machinery of the host, and use it to reproduce itself. We can use viruses as a test subject if we can find a way to easily identify or manipulate the proteins and the nucleic acids.
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  • Tobacco Mosaic Virus & Holmes Ribgrass Virus Tobacco Mosaic Virus (TMV) was the first virus discovered and isolated. TMV infects plants, and forms characteristic lesions that are identifiable as tobacco mosaic disease. Holmes ribgrass virus (HRV) also infects plants. The lesions formed in Holmes Ribgrass disease are distinctly different from TMV lesions Viruses consist of a protein coat surrounding a core of nucleic acids (RNA in the case of these 2 viruses) Viruses inject their host with their genetic material, and take over the host for the purpose of replication
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  • Heinz Fraenkel-Conrat 1955 In the first of a series of experiments, Fraenkel-Conrat enzymatically digested the protein coat from TMV viruses and isolated the RNA core (and vice versa) He then infected tobacco plants with only the protein he derived from the virus. The plants did not develop tobacco mosaic disease He also infected tobacco plants with only the RNA from his viruses. These plants developed tobacco mosaic lesions These results suggest that nucleic acids control the heredity of the virus and the characteristics associated with the viral disease Remember, protein was the favored hypothesis for the hereditary material (due to its greater structural variability)!
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  • Fraenkel-Conrat; Hybrid Viruses In this experiment, he created hybrid viruses consisting of the protein coat from HRV and an RNA core from TMV He infected tobacco plants with the hybrid viruses
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  • Fraenkel-Conrat; Hybrid Viruses If protein was the hereditary material, the plants should exhibit the symptoms of HRV If the RNA is the heredity material, the plants should form lesions characteristic of TMV
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  • Results Not only did the plants show disease symptoms characteristic of tobacco mosaic disease, but viruses collected from the infected plants were fully formed tobacco mosaic viruses. The hereditary material from the TMV core caused the disease symptoms, was replicated in the host cells, and directed the formation of TMV protein coats in the offspring viruses. That core material was RNA, not protein as hypothesized
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  • Hershey and Chase 1952 In another classic experiment to identify the hereditary material, Alfred Hershey and Martha Chase used radioactively tagged viruses (bacteriophages viruses that infect bacteria) Both protein and DNA contain carbon, hydrogen, oxygen and nitrogen, but each contains one element that the other does not. Protein contains sulfur, while DNA contains phosphorus. Viruses grown in a culture containing radioactive sulfur will tag the proteins in a way that can be identified and tracked in the lab. If viruses are grown in a culture containing radioactive phosphorus, their nucleic acids can be tracked
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  • Hershey/Chase Experiment Produce radioactively tagged viruses Allow them to infect bacteria Agitate, wash, and centrifuge the cultures Test the wash solution and the bacterial cells for radioactive residue
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  • Predictions: If protein is the hereditary material, then the wash solution should contain radioactive phosphorus residue and radioactive sulfur should be detectable in the bacterial cultures If DNA is the hereditary material, the wash solution should contain sulfur, while the bacterial culture should contain the tagged phosphorus
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  • Results and conclusions: The cells that were infected contained residues of radioactive tagged phosphorus. DNA was injected into the host cells DNA is the hereditary material
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  • Frederic Griffith 1927 Pneumonia is a deadly disease. There are various causes, including both bacterial and viral types The causes and treatment of bacterial pneumonia has been of enormous importance to medical science for generations To determine the pathogen responsible for infectious disease, a researcher will adhere to a series of logical concepts called Kochs Postulates: The bacteria must be present in every case of the disease. The bacteria must be isolated from the host with the disease and grown in pure culture. The specific disease must be reproduced when a pure culture of the bacteria is inoculated into a healthy susceptible host. The bacteria must be recoverable from the experimentally infected host.
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