U08_F08 - Unit 8 1 UNIT 8 PART A: THE GENETIC CODE PART B:...

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Unit 8 1 U NIT 8 P ART A: T HE G ENETIC C ODE P ART B: P ROTEIN S YNTHESIS P ART A: T HE G ENETIC C ODE Genetic experiments in the early 1960's conclusively proved that the genetic code words, or codons, for amino acids are triplets of nucleotides, that the codons do not overlap , and that there is no punctuation between codons for successive amino acid residues. The amino acid sequence of a protein is therefore defined by a linear sequence of contiguous triplet codons. The first AUG codon in a sequence establishes a reading frame, in which a new codon begins at every third nucleotide residue. By 1966 the base sequence of all the triplet code words for each of the amino acids had been deciphered. Assignment: Nelson & Cox, pp. 1065 - 1075. 1. Use a diagram similar to that below to discuss features of the genetic code (pp. 1066 - 1072). ... GAC CAG TCG TTG CAC . .. ... aa 1 aa 2 aa 3 aa 4 aa 5 ... In doing so, consider:
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Unit 8 2 a. The coding ratio. Given that there are four different bases, what is the minimum number of nucleotides per amino acid required to specify all 20 amino acids (p. 1066)? b. Define "codon" (p. 1066). c. Is the code overlapping or non-overlapping? Use Fig. 27-3 (p. 1066) to distinguish between each. d. Use Fig. 27-4 (p. 1067) to define "reading frame". e. Are individual codewords delimited, as for example words in a sentence are delimited by spaces (p. 1067)? f. What establishes the reading frame in RNA (p. 1069)? g. Changes in the nucleotide sequence can profoundly alter the encoded polypeptide. 1) Given a sequence of RNA, an indication of the correct reading frame, and the genetic code (Fig. 27-7, p. 1069), deduce the relevant polypeptide sequence encoded in that reading frame. 2) What are the expected consequences of a one or two base addition or deletion within the above sequence (Fig. 27-4, p. 1067)? 3) Why are such additions or deletions (when they occur in the DNA) called frameshift mutations? h. Define each of the following (pp. 1069): 1) initiation codon - 2) termination codon - 3) open reading frame i What does degeneracy refer to in the context of coding (Table 27-3, p. 1070)?
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Unit 8 3 j. Use Fig. 27-8 (p. 1071) to describe how aminoacyl tRNAs interact with mRNA. Point out the anticodon on the tRNA and the codon on the mRNA. k.
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U08_F08 - Unit 8 1 UNIT 8 PART A: THE GENETIC CODE PART B:...

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