1. Using a table that shows which codon represents which amino acid (such as Fig
ID: 207343 • Letter: 1
Question
1. Using a table that shows which codon represents which amino acid (such as Figure 8.2 in your book), determine the following: A) The possible codons that encode Arginine: B) The amino acids that could be encoded if the 2nd position of the AAA codon that encodes Lysine was changed to one of the other 3 bases: C) If you know the sequence of one codon for a particular amino acid, and you had to guess what the sequence of the other codons were, what positions would you have a better than random chance of being able to predict what the sequence was? 2. You are studying the tryptophan synthetase gene that Yanofsky also examined to determine the relationship between the nucleotide sequence and the amindo acid sequence of the gene, as illustrated in Figure 8.3). A) Yanofsky found a large number of mutations that affected the tryptophan synthetase gene. How did he find these mutations and why do you think he probably not recover missense mutations in a big stretch of the gene that encodes the part of the protein between amino acids 49 and 175? B) You start by looking at the mutations that Yanofsky recovered. One of these mutations affected amino acid number 49 and changed it from Glutamic acid to Valine. If you took this mutant E. Coli line and exposed it to a mutagen that could potentially change bases, insert bases, or delete bases, what type of second mutation could you discover that would create a wild-type tryptophan synthetase gene and where would it be located?Explanation / Answer
1.
A.
All of the possible codons that code for Arginine are:
B.The possible aminoacids would be:
C.It would be better to keep each time:any 2 positions constant and change the third one with all the bases to get all sequence of codons.For example in sequences ACG. keep AC constant and change G with all the three bases,next keep AG constant and change C with all three bases and finally keep CG constant and change A with all three bases.
2.
A.He found these mutations by seeing a change in the aminoacid sequences at position 38 in the mutants.While the mutant A23 had aminoacid Arg in place of Gly at positon 38, the mutant A46 had aminoacid Glu at position 38 in place of Gly.No missense mutation was observed in part of the gene that codes for aminoacids between 49 and 175 as there was no change in aminoacid sequences between the given stretch and this might be because that stretch of the gene did not undergo any mutation.
B.The second mutation would be a reverse mutation and that would be located in the same place where the wild type sequence was mutated so that mutated sequence is changed to original wild type sequence and in this case it would be position at aminoacid number 49.
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