Transcript DNA
Group Reading… Each group is going to be assigned a scientist/experiment to read. Each group will need to have: 2 Readers 1 Scribe (You decide in your group.) 1 Presenter After reading about your scientists experiments answer these questions about EACH!--Be ready to discuss and share with class! 1.What were the scientists trying to figure out? (what was their question?) 2.Briefly describe the experiment they did to answer their question. 3. Describe their results. (what they found out) 4. How/why are their results important to us today? DNA KWL I. Testing for DNA 1928 -scientist Fredrick Griffith isolated a harmful (smooth) bacteria and a rough (not harmful) bacteria *he was actually studying pneumonia bacteria *When he grew the bacteria in the petri plates the harmful one grew into little colonies with smooth edges *Harmless bacteria grew into little colonies with rough edges Smooth Rough – Griffith's Experiments • Griffith set up four individual experiments. • Experiment 1: Mice were injected with the disease-causing strain of bacteria. The mice developed pneumonia and died. • Experiment 2: Mice were injected with the harmless strain of bacteria. These mice didn’t get sick. Harmless bacteria (rough colonies) Lives • Experiment 3: Griffith heated the diseasecausing bacteria. He then injected the heatkilled bacteria into the mice. The mice survived. Heat-killed diseasecausing bacteria (smooth colonies) Lives • Experiment 4: Griffith mixed his heat-killed, diseasecausing bacteria with live, harmless bacteria and injected the mixture into the mice. The mice developed pneumonia and died. Heat-killed diseasecausing bacteria (smooth colonies) Harmless bacteria (rough colonies) Dies of pneumonia 1. “Dead” harmful bacteria and live safe bacteria were combined and produced live harmful bacteria 2. bacteria underwent “transformation” where one bacteria picked up the DNA (genetic info) from another bacteria * At the time he knew the bacteria had changed from harmless to harmful but he did not know that DNA was to blame Oswald Avery repeated Griffith’s work to determine which molecule was most important for “transformation” 1. Avery added enzymes to bacteria (breakdown molecules); enzymes destroyed proteins, lipids, carbohydrates, and RNA a. the mouse still died because the DNA was still being transferred! *So if all the lipids, carbohydrates, proteins and RNA were broken down what is still left? *DNA!!! 2. they discovered that DNA was responsible for the transfer of genetic information Hershey and Chase • Bacterial viruses called bacteriophage were used to show that DNA is genetic material. • The phage consisted of a DNA molecule surrounded by a protein coat. • When the bacteriophage infect bacteria, they attach to the surface and inject DNA into the cell. (the protein coat stays outside) • The first phages were covered in a radioactive label (but the DNA was not), whenthe DNA was injected into the cell, the radioactive coat stayed on the outside. • The new viruses produced in the cell contained no radioactivity. • In the second part of experiment, they made a phage that had radioactive labels on the DNA. Not on the protein coat. • When the phage infected the bacteria, the labeled DNA entered the cell and was found in the infected bacteria. • This demonstrated that the DNA, not protein, carries genetic information for a new generation of viruses. 1.Which scientist did this experiment? 2.What did the bacteria he was using cause? (what sickness) 3. What happened to the harmless bacteria in the last experiment that caused it to kill the mouse? Heat-killed diseasecausing bacteria (smooth colonies) Harmless bacteria (rough colonies) *Answer these three questions on a ¼ sheet of paper and turn in to the basket! Live disease-causing bacteria (smooth colonies) Dies of pneumonia • http://highered.mcgrawhill.com/olcweb/cgi/pluginpop.cgi?it=swf::535 ::535::/sites/dl/free/0072437316/120076/bio 21.swf::Hershey%20and%20Chase%20Experi ment