4. When a scientist makes a genetically modified bacterium as a tool for other experiments, there is always a fear that it might get out of the lab and wreck the environment. So there has been an interest in developing a âkill switch,â by which the scientist could ensure the bacterium only grows in the lab. Recently, one way to do this has been developed, wherein an artificial amino acid (that is not found in nature) is required for bacterial growth. To make this work, the artificial amino acid (call it âamacXâ) must be encoded by the bacterial mRNA, recognized by a tRNA, and must be provided as a growth factor in laboratory media.
A. Look at the Genetic Code. How would you decide which of the codons you should use to represent amacX? (There may be more than one possible choice, so focus more on general principles than on a specific codon.) Are there any codons that you couldnât use for this purpose? Why couldnât you use them?
B. The gene for which enzyme would have to be mutated to make this work? Specifically, what mutation would need to be introduced to this enzyme? [Make a sketch as part of your answer.]
C. Letâs say this organism escapes into a natural environment where there is no amacX. Make another sketch showing what a Ribosome from this bacterium would look like when it encounters an amacX codon during translation. What would happen to this Ribosome?
4. When a scientist makes a genetically modified bacterium as a tool for other experiments, there is always a fear that it might get out of the lab and wreck the environment. So there has been an interest in developing a âkill switch,â by which the scientist could ensure the bacterium only grows in the lab. Recently, one way to do this has been developed, wherein an artificial amino acid (that is not found in nature) is required for bacterial growth. To make this work, the artificial amino acid (call it âamacXâ) must be encoded by the bacterial mRNA, recognized by a tRNA, and must be provided as a growth factor in laboratory media.
A. Look at the Genetic Code. How would you decide which of the codons you should use to represent amacX? (There may be more than one possible choice, so focus more on general principles than on a specific codon.) Are there any codons that you couldnât use for this purpose? Why couldnât you use them?
B. The gene for which enzyme would have to be mutated to make this work? Specifically, what mutation would need to be introduced to this enzyme? [Make a sketch as part of your answer.]
C. Letâs say this organism escapes into a natural environment where there is no amacX. Make another sketch showing what a Ribosome from this bacterium would look like when it encounters an amacX codon during translation. What would happen to this Ribosome?
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Part B
Think about the DNA coding sequence of a gene. If an A were swapped for a T, what kind of mutation could it cause and why?
| a) It could cause a frameshift nonsense or frameshift missense mutation because it would change the reading frame of the codon triplet. | ||||||||||||||||||||||||||||
| b) It could cause a silent, missense, or nonsense mutation because those are the types that can be caused by a nucleotide-pair substitution like this one. | ||||||||||||||||||||||||||||
| c) It could cause a nonsense mutation because the sequence would no longer be the same, so the protein would be shorter and non-functional. | ||||||||||||||||||||||||||||
| d) It could cause a silent mutation because A and T are complementary to each other so it is not really a substitution mutation. Part C Why is a frameshift missense mutation more likely to have a severe effect on phenotype than a nucleotide-pair substitution missense mutation in the same protein?
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