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BELL RINGER 9-17-15 1. How is diffusion different from an ion pump? a. b. c. d. 2. Most animal cell membranes have proteins that pump ________ ions out of the cell and potassium ions into the cell. a. b. c. d. 3. Diffusion takes place due to osmotic pressure Diffusion requires the cell to use energy for the transfer of molecules Diffusion does not transfer all of the ions across the cell membrane Diffusion transfers molecules from an area of high to low concentration Calcium Carbon Magnesium Sodium Living cells use _______________ as their main source of energy. a. b. c. d. Carbohydrates Cellulose Lipids Proteins AGENDA Standard Notes – A History Lesson Timeline Closing – Crossword Puzzle STANDARD SB2. Students will analyze how biological traits are passed on to successive generations. Distinguish between DNA and RNA. Explain the role of DNA in storing and transmitting cellular information DISCOVERING DNA 3 major experiments that led to the conclusion that DNA is the genetic material in cells: Griffith’s Discovery of Transformation Avery’s Experiments with Nucleic Acids Hershey-Chase Experiment GRIFFITH’S DISCOVERY OF TRANSFORMATION When: 1928 Who: Frederick Griffith What: He was working with two related strains of bacteria One strain, S, causes pneumonia and is covered by a capsule made of polysaccharides. The other strain, R, has no capsule and doesn’t cause pneumonia. What caused the pneumonia? The bacteria or the capsule? HOW Griffith used mice to test the bacteria. S bacteria caused pneumonia. And, R bacteria is completely harmless. HOW He decided to use heat to kill the bacteria (the capsule remained). When the mice were injected with the heat killed S strain they did not get sick and die. When they were injected with heat killed S strain and live R strain they got sick and died, and live S strain was withdrawn from the dead mice Conclusion: transformation – a change in the genotype that is caused when cells take up foreign material. Huh? The R strain that was not lethal took up foreign material from the S strain and transformed into the lethal S strain WHAT CAN WE LEARN FROM GRIFFITH’S EXPERIMENTS? Genetic material can be transferred between cells. Still, no one knew that this genetic material was DNA. (That’ll come later.) AVERY’S EXPERIMENTS WITH NUCLEIC ACIDS When: 1940s Who: Oswald Avery What: He wanted to figure out if the transforming agent in Griffith’s experiment was protein, RNA, or, DNA. HOW In trying to determine if the transforming agent was DNA, RNA, or protein Avery used enzymes to destroy each of these molecules in heat-killed S bacteria. S bacteria that were missing protein and RNA were able to transform R cells into S cells. S bacteria without DNA did not transform R cells. WHAT CAN WE LEARN FROM AVERY’S EXPERIMENTS? DNA is responsible for transformation in bacteria. No idea what it looks like though! HERSHEY-CHASE EXPERIMENT When: 1952 Who: Alfred Hershey and Martha Chase What: Wanted to determine how DNA affected other cells. HOW Studied bacteriophages (viruses that infect bacterial cells and cause the cells to produce viruses) They knew that protein has sulfur but not phosphorous and DNA has phosphorous but not sulfur. http://highered.mcgrawhill.com/olc/dl/120076/bio21.swf WHAT CAN WE LEARN FROM THE HERSHEY-CHASE EXPERIMENT? DNA is the hereditary material. DISCOVERING DNA’S STRUCTURE How did Watson and Crick figure out that DNA has a double helical structure? They used information from experiments by Chargraff, Wilkins, and Franklin. CHARGRAFF’S OBSERVATIONS When: 1950 Who: Erwin Chargraff What: For each organism he studied: Amount of A=T Amount of G=C FRANKLIN AND WILKINS – PHOTOGRAPHS OF DNA When: 1952 Who: Rosalind Franklin and Maurice Wilkins What: Developed high-quality x-ray diffraction images of DNA The images suggested that a DNA molecule resembled a tightly coiled helix made of two chains of nucleotides. WATSON & CRICK When: 1953 Who: James Watson and Francis Crick What: Set out to physically build a 3D model of DNA Took into account Chargraff’s data and Franklin’s x-ray diffraction studies Also used their knowledge of chemical bonding HOW Used paper models of the bases to figure out the base pairs of pyrimidines with purines. Made a 3D model of a DNA double helix using tin, wire, and other materials. TIMELINE Use the pictures, dates, and names provided to create an accurate timeline. Be sure to include a summary of the experiments and conclusions Griffith Avery Chargraff Franklin