Presentation on theme: "CHAPTER 9.1 Identifying the Genetic Material Grade 10 Biology Spring 2011."— Presentation transcript:
CHAPTER 9.1 Identifying the Genetic Material Grade 10 Biology Spring 2011
Bell Ringer 1. Describe the structure of a chromosome 2. Define the term gene 3. 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 Procedure:Inject S strain into mice Inject R strain into mice Inject heat- killed S bacteria into mice Inject heat- killed S bacteria & R strain bacteria into mice Results:All mice dieAll 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
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: xKitsd0&feature=related xKitsd0&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 #1Part #1Part #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 #2Part #1Part #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 #3Part #1Part #2 Observations- removing viruses from bacteria Removed S phages from bacteria surface. Separated phages and bacteria. Found that most of the S- label 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 P- label 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 P- labeled 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: 5b0/ 5b0/ Avery: Griffith: g g
Review 1. 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. 2. T/F Avery’s experiments clearly demonstrated that he genetic material is composed of DNA. 3. T/F The experiments of Hershey and Chase cast doubt on whether DNA was the hereditary material.
Answers 1. 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. 2. T Avery’s experiments clearly demonstrated that he genetic material is composed of DNA. 3. F The experiments of Hershey and Chase cast doubt on whether DNA was the hereditary material.