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CHAPTER 9.1 Grade 10 Biology Spring 2011 Identifying the Genetic Material Bell Ringer 1. 2. 3. Describe the structure of a chromosome Define the term gene When in the cell cycle is DNA copied? Bell Ringer- Answers A chromosome consists of two replicated strands of DNA tightly coiled around proteins. The two strands, called chromatids, are attached at a point celled a centromere. A gene is a segment of DNA that codes for a protein or RNA molecule A cell’s DNA is copied during the synthesis (S) phase Objectives Relate Griffith’s conclusions to the observations he made during the transformation experiments Summarize the steps involved in Avery’s transformation experiments, and state the results Evaluate the results of the Hershey and Chase experiment Identifying the Genetic Material Mendel explained why you resemble your parents. Why? Raised questions of what are genes made of? Griffith’s Experiments In 1928 Fredrick Griffith: bacteriologist Was trying to prepare a vaccine against pneumonia Vaccine: substance that is prepared from killed or weakened disease-causing agents, including certain bacteria Griffith’s Experiments Worked with 2 types, or strains, of S.pneumoniae Strain #1: Enclosed in a capsule composed of polysaccharides Capsule protects bacterium from body’s defense Virulent: able to cause disease Forms smooth colonies (S strain) Griffith’s Experiments Strain #2: Lacks polysaccharide capsule and does not cause disease Forms rough colonies (R strain) Griffith’s Experiments Experiment: Experiment #1 Experiment #2 Experiment #3 Experiment #4 Starts with: Mice are alive Mice are alive Mice are alive Mice are alive Procedure: Inject S strain into mice Inject R strain into mice Inject heatkilled S bacteria into mice Inject heatkilled S bacteria & R strain bacteria into mice Results: All mice die All mice live All mice live All mice die Griffith’s Experiments Results: The heat-killed S strain still had their capsule When Griffith injected mice with heat-killed S bacteria, the mice still lived This meant that it was not the capsule that killed the mice When injected mice with heat-killed S and R strain bacteria mice died Blood showed that the live R bacteria had acquired capsules The R had been changed and became virulent Transformation: change in genotype caused when cells take up foreign genetic material Griffith’s Experiments Results: When injected mice with heat-killed S and R strain bacteria mice died Blood showed that the live R bacteria had acquired capsules The R had been changed and became virulent Transformation: change in genotype caused when cells take up foreign genetic material Did not know what was causing this transformation Avery’s Experiments 1944 Compared the activity for the material responsible for transformation Looked at protein (polysaccharide capsule) and DNA Demonstrated that DNA is the material responsible for transformation DNA contains the instructions for the making of the capsule in the S strain bacteria Avery’s Experiments Hershey-Chase Experiments 1952 It was known that viruses are composed of DNA or RNA surrounded by a protective protein coat Bacteriophage: virus that infects bacteria Was known the when phages infect bacteria they are able to produce more viruses, which are released when the bacterial cells rupture Hershey-Chase Experiments Bacteriophage video: http://www.youtube.com/watch?v=_J9xKitsd0&feature=related Needed to figure out how bacteriophage reprograms the bacteria to make new viruses Is it the DNA, protein or both responsible? Hershey-Chase Experiments DNA: only molecule inside phage that contains phosphorous Protein: only molecule inside phage that contains sulfur Hershey-Chase Experiments Step #1 Part #1 Part #2 Labeling bacteriophages. Used T2 bacteriophage and E.coli (bacteria). Grew in nutrients that contained sulfur so T2 took up sulfur in its protein coat. Used T2 bacteriophage and E.coli (bacteria). Grew in nutrients that cotained phosphorous so T2 took up phosphorous in its DNA. Hershey-Chase Experiments Step #2 Part #1 Part #2 Infecting E. coli. The S-labeled phages infected the E. coli. S was radioactive so could be traced. The P-labeled phages infected the E.coli. P was radioactive so could be traced. Hershey-Chase Experiments Step #3 Part #1 Part #2 Observations- removing viruses from bacteria Removed S phages from bacteria surface. Separated phages and bacteria. Found that most of the Slabel was part of the phage. Meaning that the protein was not injected into the bacteria. Removed P phages from bacteria surface. Separated phages and bacteria. Found that most of the Plabel was part of the bacteria. Meaning that the DNA was injected into the bacteria. Also, the new phages produced by the bacteria also contained the Plabeled DNA. Hershey-Chase Experiments Conclusions: DNA is injected into bacterial cells, proteins remain outside of the bacterial cells Injected DNA cause the bacteria to produce more viral DNA and proteins This means that the DNA (not the protein) is the hereditary material, at least in viruses Identifying the Genetic Material Further experiments have shown that DNA is the molecule that stores genetic information in living cells Videos Hershey Chase: http://www.tudou.com/programs/view/x5FYaoM8 5b0/ Avery: http://www.youtube.com/watch?v=RWFc8Iqz4Jg Griffith: http://www.youtube.com/watch?v=vQOdDGM5vS g Review 1. 2. 3. T/F Griffith’s experiments with S.pneumoniae in mice showed that harmless bacteria could turn virulent when mixed with heat killed bacteria that cause disease. T/F Avery’s experiments clearly demonstrated that he genetic material is composed of DNA. T/F The experiments of Hershey and Chase cast doubt on whether DNA was the hereditary material. Answers 1. 2. 3. T Griffith’s experiments with S.pneumoniae in mice showed that harmless bacteria could turn virulent when mixed with heat killed bacteria that cause disease. T Avery’s experiments clearly demonstrated that he genetic material is composed of DNA. F The experiments of Hershey and Chase cast doubt on whether DNA was the hereditary material.
