12. In the 1950s, the race to solve the secondary structure of DNA became intens
ID: 144084 • Letter: 1
Question
12. In the 1950s, the race to solve the secondary structure of DNA became intense. In an uncharacteristic rush to publish, Linus Pauling erroneously proposed a triple-stranded structure in February 1953. This model had the nitrogenous bases on the exterior and the sugar-phosphate backbones clustered in the middle. How does the orientation of the sugar-phosphate backbone in this model compare with the one proposed by Watson and Crick? Do you think Pauling's structure could exist in cells? Why or why not?Explanation / Answer
Please find the answers below:
Answer 12: According to the information, Pauling's DNA structure contained a triple-helix, with nitrogenous base on the periphery and sugar-phosphates in the middle. However, the actual Watson-Crick model of DNA describes the DNA as a double-helix having nitrogenous base in the middle with sugars-phosphates in the periphery. The triple-helix is not reasonable in nature because the nitrogenous base on the outside will tend to generate multiple hydrogen bonds with the water molecules in the cytoplasm/nucleus. This will disorient the secondary structure of DNA and it will be no longer present in the tertiary complex form. Thus, this model of DNA is not practical in nature.
Answer 14: According to the tabulated quantitative data, it can be clearly seen that the purines as well as pyrimidines have equal content in the DNA. This is why all the organisms listed here have almost similar ratio of purines to pyrimidine content in their DNA. Thus, the single combination of a purine and pyrimidine can imply a double-helix but not a quadruplet which will mean a quadra-helix.
Answer 15: The experimental results of Chargaff yielded that the nucleic acid contained an equal number of guanine and cytosine as well as adenine and thymidine/urcils. This idea infused the Watons and Crick model of DNA suggesting complementary base pairing. However, even if these results were observed using RNA as sample, the rules would not have changed becuase transcriptional assays demonstrate that RNA too undergoes complementary base pairing with the rules similar to DNA.
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