Theoretical Test

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4. The Chemistry of DNA (5pts)4-1. In 1944 Oswald Avery isolated a genetic material and showed, byelemental analysis, that it was a sodium salt of deoxyribonucleic acid. Asegment of DNA with formula mass of 1323.72 is shown.Assuming that equimolar amounts of the four bases are present in DNA,write the number of H atoms per P atom. Calculate, to 3 significant6
figures, the theoretical weight percentage of H expected upon elementalanalysis of DNA.4-2. Chargaff extracted the separated bases and determined theirconcentrations by measuring UV absorbance. The Beer-Lambert lawwas used to obtain the molar concentration. Chargaff discovered thefollowing molar ratio for bases in DNA:adenine to guanine = 1.43 thymine to cytosine = 1.43adenine to thymine = 1.02 guanine to cytosine = 1.02Chargaff’s discovery suggested that the bases might exist as pairs inDNA. Watson and Crick mentioned in their celebrated 1953 paper inNature: "It has not escaped our notice that the specific pairing we havepostulated immediately suggests a possible copying mechanism for thegenetic material."Draw structures of the specific pairing found in DNA. Indicate hydrogenbonds. Omit the sugar-phosphate backbone.4-3. Mutation can occur through base pairings different from the above.Draw structures of any three alternative base pairs.4-4. The plausibility of the formation of purine and pyrimidine bases in theprebiotic atmosphere of the Earth from HCN, NH 3 , and H 2 O has beendemonstrated in the laboratory. Write the minimum number of HCN andH 2 O molecules required for formation of the following compounds.NH 2OONH 2NNNNHNHNNHNNHNNH 2NHONHOadenineguanineUracilcytosine7
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Theoretical Test

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