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GENETICS 2: DNA STRUCTURE AND FUNCTION 1.Explain how DNA was discovered: In 1868, Miescher found DNA in pus cells and fish sperm, but he didn’t know what it was. 2.What organisms did Fred Griffith experiment with? S – strain of pneumonia causing bacteria that caused pneumonia and a R – strain that did not cause pneumonia. 3. Compare and contrast the organisms used by Griffith: . The S – strain and the R – strain are the same bacteria except that the s – strain has a sticky outer capsule to stick to its host and the R – strain has no capsule. 4.What is BACTERIAL TRANSFORMATION? When one bacteria comes into contact with another bacteria. It will take a portion of the other bacteria’s DNA and gain new traits. 5. Summarize the Fred Griffith experiments that led to the accidental discovery of bacterial transformation: He injected mice with R cells, and the mice lived. He then injected mice with S cells and the mice died, live s cells found in the mouse blood. S – cells were heated, then injected into the mice, and the mice lived. Dead S cells and live R cells were injected into the mice. Mice died. Live S cells found in the mouse blood. 6. What were the final results of the Fred Griffith Experiments? . Some unknown transformation factor had changed the harmless R cells into deadly S cells that caused pneumonia. 7.What new characteristic had been gained by the bacteria in the Griffith experiments? The R cells began to develop a sticky outer capsule. .8. What two substances were suspected of causing the bacterial transformation ? PROTEIN and NUCLEIC ACID . . 9.Who was the first scientist to claim that DNA was the one responsible for the transformation? OSWALD AVERY 10. Who were Hershey and Chase? . Two scientist who run a series of experiments with viruses and bacteria that proved that DNA was the part responsible for bacterial transformation. 11.What is a bacteriophage and why was it chosen for the Hershey and Chase experiments? The bacteriophage is a virus that invades bacteria cells. The bacteriophage was selected because it is only made up of a strain of DNA and a protein coat. .12. Explain the Hershey and Chase experiments: (4) (a)The outer protein coat of the virus was labeled with radioactive sulfur. (b)The nucleic acid was labeled with radioactive phosphorus. (c)The radioactively tagged virus was observed invading a bacteria cell. (d)It was noticed that the sulfur labeled protein stayed outside the cell and the phosphorus tagged nucleic acid went inside and took over the cell. 13. What did the Hershey and Chase experiments prove? . The Hershey and Chase experiment proved that it was the nucleic acid that was the transforming factor. 14.What is a nucleotide? The sub unit that DNA is made of. Chains of nucleotides make up a DNA molecule. 15. Describe a nucleotide (structure) . It contains: (a)A five carbon sugar (b)A phosphate group (c)One of four nitrogen bases: A = Adenine T = Thymine G = Guanine C = Cytosine 16. What makes one nucleotide different from the others? T and C are single ringed pyrimidines and A and G are double ringed purines.. . Double ring structures Single ringed structures 17.What did Edwin Chargaff observe about these nucleotides? (a)All animal species have the same nitrogen bases in their DNA, but in different amounts. (b)In all animal species, “A” always bonded with “T” and “C” always bonded with “G”. 18 State the techniques used by Rosalind Franklin in studying DNA and list her discoveries: Technique: Franklin used X-Ray diffraction to produce images of DNA.. Discoveries: (a)DNA exist as a long thin molecule of uniform diameter. (b)The DNA structure tends to repeat itself. (c)DNA is helical. 19.Who were Watson and Crick? College students who won the Nobel prize for creating the first true model of the DNA molecule. 20.How did Watson and Crick get the data needed for their model? They collected data from the work of earlier scientist. .21. State the three things that were demonstrated in the Watson and Crick Model: (a)“A” always bonds with “T” and “G” always bonds with “C”. (b)The backbone (or sides of the ladder) were made of chains of sugar – phosphate linkages. (c)The molecule was double stranded and looked like a twisted ladder. 22.What makes one species genetically different from other species? The sequences of bases are different. 23. Draw, color and label a simple version of the Watson and Crick Model. COLOR ALL IDENTICAL SOMPONENTS THE SAME COLOR, DIFFERENT ITEMS DIFFERENT COLORS. .24. What holds one side of the DNA “ladder” to the other side of the DNA “ladder”? Hydrogen bonding between the base pairs. .25. Explain DNA replication: (a)An enzyme called DNA helicase breaks the hydrogen bonds between the base pairs and UNZIPS the ladder. (b)DNA polymerase brings in free floating nucleotides from the cytoplasm and attaches them to the exposed bases. (c)DNA ligase seals the new nucleotides to the growing strand. .26. Why is DNA replication considered “semi-conservative” replication? Each replicated chromosome contains one old side and one new side. .27. Do wrong base pairs ever connect together? If so, what would happen? How is this prevented? Yes it happens. The chromosome would not function properly. The replicate is proof read by DNA polymerase and the incorrect bases are replaced by the correct ones. 28.What prevents the DNA from tangling up as it forms human chromosomes? (a)Histones spool up the DNA into units called nucleosomes. (b)Another histone stabilizes the DNA into loops. (c)Another histone arranges the loops into “domains”. .That’s all until next time. . . . . . . .