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

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: 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.