Slide 1 / 155 New Jersey Center for Teaching and Learning Progressive Science Initiative This material is made freely available at www.njctl.org and is intended for the non-commercial use of students and teachers. These materials may not be used for any commercial purpose without the written permission of the owners. NJCTL maintains its website for the convenience of teachers who wish to make their work available to other teachers, participate in a virtual professional learning community, and/or provide access to course materials to parents, students and others. Click to go to website: www.njctl.org Slide 2 / 155 AP BIOLOGY GENES September 2011 Henriquez, Lageman, Satterfield www.njctl.org Slide 3 / 155 Genes Unit Topics Click on the topic to go to that section · Discovery of DNA · DNA Structure & Semi-Conservative Replication · DNA Replication · RNA Transcription · Gene Expression, Central Dogma · Three Types of RNA, Translation · Article Discussion Day
Slide 4 / 155 Discovery of DNA Return to Table of Contents Slide 5 / 155 Deoxyribonucleic Acid Recall that a DNA is a molecule that stores and transmits genetic information. Slide 6 / 155 DNA To understand the "secret of life" scientists had to figure out the chemical and physical nature of the gene - the factor passed from parent to offspring that directs the activity of the cell and determines traits. By applying basic principles of physics and chemistry and keeping up on the latest discoveries of their time, a group of remarkable scientists were able to determine the structure of DNA.
Slide 7 / 155 DNA and Modern Medicine The discovery of the structure and function of DNA has led to astounding leaps in understanding of biology, heredity, and modern medicine. "It's impossible to overstate the importance of knowing the structure of DNA." - Francis Collins, Director of the Human Genome Project Click Here to see a DNA timeline Slide 8 / 155 "Standing on the Shoulders of Giants" The proof that DNA is the carrier of genetic information involved a number of important historical experiments. These include: Griffith Transformation Experiment Avery-Macleod-McCarty Experiment Hershy-Chase Experiment Contributions of Watson, Crick, Wilkins, and Franklin Slide 9 / 155 Griffith and Transformation In 1928 British Scientist Frederick Griffith was conducting experiments with mice to determine how bacteria made people sick. Griffith isolated two different strains of pneumonia bacteria from mice and grew the bacteria on petri dishes in the lab.
Slide 10 / 155 Griffith's Colonies One strain grew in rough colonies and did not cause disease. The other strain grew in smooth colonies and caused disease. Caused disease Did not cause disease R strain S strain colonies colonies Slide 11 / 155 Mice and the 2 strains When he injected the mice with the rough (R) strain, they lived. When he injected the mice with the smooth (S) strain, they died. However, when he heated the S strain of bacteria, killing them, and then injected the heat-killed S strain bacteria into the mice, they did not die. Slide 12 / 155 Mouse Mortality Heating the S strain killed the bacteria and prevented them from passing disease to the mice.
Slide 13 / 155 Griffith Experiment Part 2 Griffith then mixed heat-killed disease-causing S strain bacteria with live, harmless R strain bacteria and injected this mixture into mice. Before neither heat-killed S strain or live R strain bacteria made the mice sick, but the mixture of the two caused the mice to develop pneumonia and die. Slide 14 / 155 Griffith: Part 2 Slide 15 / 155 What was in the mice lungs? Griffith examined the lungs of mice that had been infected with the mixture of dead S strain and live R strain bacteria and found them filled with disease-causing bacteria. This indicated that a chemical factor was transferred from the dead S strain bacteria to the live R strain bacteria that transformed them into disease-causing bacteria.
Slide 16 / 155 What was the chemical factor? He also noted this factor was passed on as the bacteria reproduced. Slide 17 / 155 1 What is bacterial transformation? The inheritance of genetic material A The exchange of genetic material between B strains of bacteria The interaction between strains of bacteria C The passage of genetic material from parent D to offpsring Slide 18 / 155 2 Why was Griffith's experiment significant? It showed that a chemical factor transformed A R strain bacteria into S strain bacteria It proved dead bacteria could still transmit B disease directly to mice It indicated proteins were the source of C genetic material None of the above D
Slide 19 / 155 Avery, Macleod, MacCarty Oswald Avery, Colin MacLeod, and Maclyn McCarty were the first to demonstrate that DNA was the substance that caused bacterial transformation. Avery's group built on Griffith's work to determine which chemical was responsible for transforming the R strain bacteria. In the 1930s and 1940s, at the Rockefeller Institute for Medical Research in New York City, Avery and his colleagues suggested that DNA, rather than protein as was believed at the time, was the hereditary material in bacteria. Slide 20 / 155 Avery's Experiment First they repeated Griffith's experiment by mixing heat-killed S strain and R strain bacteria and verifying transformation occurred.Then they lysed the S cells by adding detergent. Detergent disrupts the cell membrane and cell wall, causing the DNA, RNA, proteins and other molecules to spill out. They mixed the S lysate with R strain bacteria and determined that the contents of cell parts in the Lysate S lysate still allowed transformation to occur. Slide 21 / 155 Their Three Mixtures Next they mixed heat-killed S strain lysis containing DNA, RNA, and Protein with R strain bacteria and allocated the mixture into three test tubes: To tube A they added DNase - an enzyme that destroys DNA molecules. To tube B they added RNase. To tube C they added Protease. Finally, they injected each mixture into the mice and waited for results.
Slide 22 / 155 3 What does the enzyme RNase do? Breaks down RNA molecules A Synthesizes RNA molecules B Breaks down proteins C Synthesizes proteins D Slide 23 / 155 4 If DNA were the molecule being transferred from dead S strain bacteria to live R strain bacteria, then the mice injected with DNase treated bacteria would most likely Survive A Die B Remain unaffected C Pass on pneumonia to their offspring D Slide 24 / 155 Avery's Results The results of the experiment showed that the mice injected with both the RNase and Protease treated bacterial cells died. However, the mice injected with the DNase treated bacterial cells survived. *Destroying the DNA prevented transformation of R strain bacteria.
Slide 25 / 155 5 What did Avery's experiment prove? Bacteria can exchange genetic information A DNA is the molecule that causes bacterial B transformation RNA and Proteins are the molecules responsible for C transferring genetic information DNase breaks down DNA molecules D Slide 26 / 155 Hershey and Chase Alfred Hershey and Martha Chase conducted a series of experiments helping to confirm that DNA was the genetic material in cells. Hershey and Chase showed that when viruses (made of proteins and DNA) infect bacteria, their DNA enters the host cell but most of their proteins do not. Hershey shared the 1969 Nobel Prize in Physiology for his work involving the genetic nature of viruses. Slide 27 / 155 The Hershey Chase Experment
Slide 28 / 155 6 What would you expect to see if protein had been injected into the cell instead? Red-labeled cells A Green-labeled cells B Cells containing phosphorous C Cells containing oxygen D Slide 29 / 155 DNA Structure & Semi- Conservative Replication Return to Table of Contents Slide 30 / 155 Structure of DNA In 1962, the Nobel Prize in Physiology and Medicine was awarded to James Watson, Francis Crick, and Maurice Wilkins for their determination of the structure of DNA in 1953. Unfortunately, the rules of the prize award state it can only go to the living. This meant Wilkin's colleague Rosalind Franklin who collected all the data they used could not receive honor. Franklin died at the age of 37 in 1958 from ovarian cancer which is thought to be the result of her work with X-ray radiation incurred while doing the research.
Slide 31 / 155 X-ray Crystallography Franklin and Wilkins used a technique called X-ray crystallography to discover more information about the structure of DNA. X-ray crystallography is a method of determining the arrangements of atoms within a crystal. When X-rays (a type of electromagnetic wave) strike a crystal, they diffract around electrons. The angles and intensities of diffracted beams can be used to determine the position of atoms and chemical bonds. This diffraction pattern indicated the double helical shape of DNA Slide 32 / 155 Watson and Crick's Double Helix Using information from the work of Wilkins and Franklin, James Watson and Francis Crick were the first to propose the double helical nature of DNA. Francis Crick is also well known for coining the term "central dogma" regarding the flow of genetic information from DNA to RNA to protein. The day they discovered the helix in 1953, they are said to have left their lab, walked into a pub in Cambridge, England and interrupted the patrons' lunchtime shouting " we have discovered the secret to life !" Slide 33 / 155 Double Helix
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