How Does The Mismatch Repair Pathway Identify The Incorrect Base In E. Coli?

University of Minnesota - Twin Cities

Gamow (1954) proposed that the structure of DNA deduced by Watson and Crick (1953) could be interpreted as a fashion of forming roughly 20 "words" of the mutual amino acids from the 4 "letters" A, T, C, and Grand that represent DNA nucleotides. Crick and coworkers (1961) used a method developed by Benzer to induce mutations in the Deoxyribonucleic acid of a virus by the insertion of a single nucleotide. The mutant could not infect the bacterium Escherichia coli and neither could viruses with a 2nd insertion of a second Deoxyribonucleic acid nucleotide. However, a third nucleotide insertion restored the ability of the virus to infect the bacterium. In 1961, Nirenberg and Matthaei conducted a series of experiments to better understand the period of genetic information from gene to protein. They discovered that in solutions containing the contents of ruptured E. coli bacterial cells from which DNA had been removed, polymers containing only one repeating amino acrid, phenylalanine, would be synthesized if synthetic mRNA equanimous of only the single nucleotide, uracil (U), was added to the solution in which phenylalanine was besides present. In solutions containing mRNA with only adenine (A) or cytosine (C) and the amino acids lysine or proline, polymers containing only these amino acids would be synthesized. The researchers found that when ribosomes were removed by filtration, these polymers did non class. Nirenberg and Leder (1964) extended this work to include other nucleotides. A. Summarize the conclusions regarding the encoding and decoding of heritable information supported by these studies. Explain how these studies provided evidence to back up the Triplet Lawmaking. Khorana (1960) developed a technique for synthesizing RNA composed of predictable distributions of repeated pairs or triplets of nucleotides. He plant, for example, that RNA synthesized when A and U were present in relative concentrations of 4:ane, respectively, will produce RNA sequences with these distributions determined by their relative probabilities: AAU:AAA, AUA:AAA, and UAA:AAA; $0.8^{ii} \times 0.2 / 0.viii^{3}=i / 4$ [calculated every bit follows: i) 4/5 of the bases are A, so the likelihood of selecting A is 0.8; ii) the selection is repeated to determine the 2nd letter of the iii-letter codon; iii) the likelihood of selecting a U is 1 in five; iv) the probability of selecting the set AUU is the production; v) similarly, the probability of AAA is $(4 / 5)^{3}$ ; and half-dozen) the ratio of these probabilities is their relative likelihood]: AUU:AAA, UUA:AAA, and UAU:AAA; $0.8 \times 0.two^{2} / 0.8^{3}=ane / xvi$ and UUU:AAA; $0.2^{three} / 0.8^{3}=1 / 64$ B. Based on Khorana'southward findings, calculate the relative distributions of the following ratios of concentrations of RNA triplet sequences from mixtures in which the relative concentrations of guanine and cytosine, G:C, are 5:1. C. Based on the work of Nirenberg, Matthaei, Leder, and Khorana, the following table was constructed (taken from Khorana's Nobel Prize address): D. Describe the effects of the codons UAA, UAG, and UGA on poly peptide synthesis.

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