Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Chap 13: DNA - Genetic Material QUESTION: Where is genetic information stored? a) b) c) d) in the ribosomes of cells within the proteins of cells within the DNA of cells within the membrane of cells *It is important to remember that scientists didn’t always have the answers, experiments and research must be performed and consensus reached. Science is a process! The answer is here somewhere! Finding the molecule of heredity The material must be… 1.Able to store information that pertains to the development, structure and metabolic activities of the cell 2.Stable so that it can be replicated 3.Able to undergo changes (mutations) 1869 – Discovering Nucleic Acids Swiss Physician, Johannes Friedrich Miescher isolated the chemical he called “nuclein” from the nuclei of white blood cells Now called nucleic acids DNA (deoxyribonucleic acid) RNA (ribonucleic acid) Miescher used pus and bloodstained bandages from a hospital to study “nuclein” NUCLEOTIDES (found in nuclein) Contain a sugar, phosphate and a nitrogen base Four types of Nitrogen Bases Adenine Guanine Cytosine Thymine ***THE BIG QUESTION*** Is it nucleic acids that contain the genetic code or is it proteins? a) Proteins contain 20 amino acids that can be organized in countless ways to determine traits b) Nucleic acids only contained 4 different nucleotides 20 amino acids As a storage molecule amino acids would have a lot of options, you could combine these in different ways Only 4 bases would seem to not have as much versatility It’s like have an alphabet of 20 letters versus and alphabet of 4. TRANSFORMATION OF BACTERIA Frederick Griffith attempted to find a vaccine against pneumococcus He found that one type of bacteria could turn into another An overview of the transformation experiment. Can you summarize this in your own words? DNA WAS DETERMINED TO BE THE TRANSFORMING SUBSTANCE ●DNA from S strain bacteria causes R strain to be transformed ●Enzymes that degrade proteins will not stop the transformation ●Enzymes that degrade DNA does stop the transformation Transformation Animation Activity Quick Recap: 1) What caused scientists to believe that proteins contained the genetic code? 2) What was Miescher’s contribution to genetic studies? 3) How were the nonvirulent R strain bacteria transformed into a virulent strain? 4) Griffith’s experiment resulted in which conclusion? a) DNA contains the genetic code; it is the transforming agent b) Proteins contain the genetic code, they are not destroyed during heating c) Bacteria can spontaneously come to life after being heat killed. Alfred Hershey and Martha Chase Experiments Remember the bacteriophage!!? It’s back! What do you remember about phages? Bacteriophages – viruses that infect bacteria ●Consist of a protein capsid ●A core of DNA (or RNA) ●Experiments used radioactive sulfur to tag the protein ●And radioactive phosphorous to tag the DNA ●The goal was to see which substance (protein or DNA) moved into the infected cell Conclusion: The radioactive tag on the DNA went into the bacteria, not the tagged proteins Animation of the Hershey and Chase Experiment 1. What part of the phage entered the bacterial cell following infection? A)DNA B)RNA C)protein coat D)the entire phage E)no part 2. If 35S was found in progeny phages rather than 32P, Hershey and Chase would have concluded that A)proteins contain phosphorus. B)DNA contains sulfur. C)phage DNA enters the host cell. D)phage protein enters the host cell. E)phage can kill the E. coli cell. 3 3. In the Hershey and Chase experiment, radioactively-labeled A)32P did not enter the cell. B)32P remained inside the cells after vigorous shaking. C)32P was removed from the cells by vigorous shaking. D)32P and 35S remained inside the cells after vigorous shaking. E)32P and 35S were removed from the cells after vigorous shaking. Lecture Reflection 1) How was DNA established as the molecule that contains the genetic code? 2) Now is a good time to mention that at this point, no one knew the structure of DNA, they only had a basic idea of what it was made of, but not its shape. Every basic biology student knows the shape of DNA now, can you sketch it? THE RACE IS ON! Who will be the first to discover the structure of DNA?