Historical Perspective - Application of Biology - Lecture Notes, Study notes of Biology

Download Historical Perspective - Application of Biology - Lecture Notes and more Study notes Biology in PDF only on Docsity! HISTORICAL PERSPECTIVES: The Search for the Genetic Code We have been establishing the foundation for our heredity unit. Through our readings and research we have discovered that proteins are responsible for the expression of traits—physical traits as well as traits associated with cellular operations. We have studied the structure of proteins and found that they are organic molecules made up of a series of amino acids. The characteristic of a protein is determined by the sequence and number of amino acids. We have learned that if the amino acid sequence is altered, the protein is altered, and so is the trait. Our next step is to determine WHAT CONTROLS THE PRODUCTION OF PROTEINS? Since proteins control traits, then whatever controls protein production is responsible for all of the traits of cells and subsequently organisms. The search for the genetic material was a long one. Many scientists contributed to what we now know about genetics and the control of protein production. Your goal today is to analyze the research that led to what we now know about genetics. Do the following readings and complete the exercises. Answer the questions on your own sheet of paper. Do not write on this sheet. EXERCISE 1: Fred Griffith and Transformation Read the section entitled Griffith and Transformation in your textbook. 1. What did Griffith hope to learn from his experiment? 2. What was the independent variable in Griffith’s experiment? 3. What was the dependent variable in Griffith’s experiment? 4. What two organisms were involved in Griffith’s experiment? 5. Griffith described his discovery as transformation. Why was this an appropriate description? 6. What information did Griffith’s experiment contribute to the early study of genetics? Griffith’s experiment prompted a lot of study in the scientific community. What was the genetic substance that passed on information, that determined an offspring’s visible traits, that was able to “transform organisms”, and also that accounted for the incredible diversity to be found among living things? Some scientists thought it must be a protein, because proteins are present in large quantities in the cell and carry on numerous functions. Proteins are made of 20 different subunits called amino acids that can be joined in a great variety of combinations. Supporters of proteins as the molecule of heredity thought that this variety would allow for the diversity we see in organisms, much as the 26 letters of the English alphabet placed in a variety of ways produce an immense quantity of words. Other scientists, noting that large amounts of DNA were also present in cells, thought that DNA was the molecule of heredity. However, it seemed too simple a molecule, with only six subunits: deoxyribose (a sugar), phosphate, and four nitrogenous bases (adenine, guanine, thymine, cytosine). What was the molecule of heredity? Was it protein or was it DNA? EXERCISE 2: Oswald Avery Read the section entitled Avery and DNA in your textbook. 7. How did Avery build on scientific information that was already available as he did his experiment? 8. Briefly describe Avery’s experiment. 9. What was Avery’s contribution to what we know about the molecule of heredity? EXERCISE 3: Hershey and Chase Read the section entitled The Hershey-Chase Experiment in your textbook. 10. What is a bacteriophage? What does it do? 11. What chemical difference between DNA and protein did Hershey and Chase take advantage of in their experiment? 12. What was the independent variable in their experiment? 13. What was the dependent variable in their experiment? 14. What were the results of Hershey and Chase’s experiment? 15. What very important conclusion did they draw? The function of DNA as the storage site and transmitter of information for traits was now known. But, what was its structure? How were the subunits arranged in the molecule so that DNA could be the bearer of vast amounts of information and code for the incredible diversity seen in living things? EXERCISE 4: Chargaff Read the section entitled, Chargaff’s Rules in your textbook. Erwin Chargaff added an important piece to the puzzle with his experiments showing the proportions of nitrogenous bases found in DNA were the same in every cell of an organism in a given species, but that the proportions varied from species to species. Examine his results in the following table. Docsity.com