Textbook Question
A research scientist is interested in producing human insulin in the bacterial species E. coli. Will the genetic code allow the production of human proteins from bacterial cells? Explain why or why not.
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11. Translation
The Genetic Code
0:29 minutesProblem 29d
Textbook Question
Shown here are the amino acid sequences of the wild-type and three mutant forms of a short protein.
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Wild-type: Met-Trp-Tyr-Arg-Gly-Ser-Pro-Thr
Mutant 1: Met-Trp
Mutant 2: Met-Trp-His-Arg-Gly-Ser-Pro-Thr
Mutant 3: Met-Cys-Ile-Val-Val-Val-Gln-Hi
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Use this information to answer the following questions:
Of the first eight wild-type triplets, which, if any, can you determine specifically from an analysis of the mutant proteins? In each case, explain why or why not.
Verified step by step guidance1
Step 1: Understand that each amino acid in a protein is encoded by a triplet of nucleotides called a codon in the DNA sequence. The wild-type protein sequence is given as Met-Trp-Tyr-Arg-Gly-Ser-Pro-Thr, which corresponds to eight codons in order.
Step 2: Compare the mutant protein sequences to the wild-type sequence to identify which amino acids are preserved, missing, or changed. Mutant 1 has only Met-Trp, indicating truncation after the second amino acid. Mutant 2 has Met-Trp-His-Arg-Gly-Ser-Pro-Thr, differing at the third amino acid (His instead of Tyr). Mutant 3 has a completely different sequence starting with Met-Cys-Ile-Val-Val-Val-Gln-Hi, indicating multiple changes.
Step 3: For each of the first eight wild-type codons, determine if the corresponding amino acid can be confidently assigned based on the mutant sequences. For example, the first two codons (Met and Trp) appear in Mutants 1 and 2, confirming their identity. The third codon (Tyr) is replaced by His in Mutant 2, so the original codon for Tyr can be inferred but with caution due to mutation.
Step 4: Consider that if an amino acid is unchanged in a mutant, the codon likely remains the same or codes for the same amino acid (due to codon redundancy). If the amino acid is missing or replaced, the original codon cannot be definitively determined from that mutant alone.
Step 5: Summarize which codons can be specifically determined based on the presence or absence of amino acids in the mutants, explaining that only codons corresponding to amino acids conserved in mutants can be confidently assigned, while those replaced or missing cannot be precisely identified.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Genetic Code and Codon Specificity
The genetic code consists of triplet codons in mRNA that specify particular amino acids during protein synthesis. Each codon corresponds to one amino acid, and changes in codons can alter the amino acid sequence. Understanding codon specificity helps determine which wild-type triplets can be inferred from mutant protein sequences.
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Types of Mutations and Their Effects on Protein Sequence
Mutations such as deletions, insertions, or substitutions can change the amino acid sequence of a protein. Analyzing how these mutations alter the sequence helps identify which original codons remain unchanged or are replaced, providing insight into the wild-type triplets that can be deduced.
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Protein Sequence Alignment and Comparative Analysis
Comparing mutant protein sequences to the wild-type sequence allows identification of conserved and altered regions. This alignment helps pinpoint which amino acids—and thus which codons—are preserved or changed, enabling inference about specific wild-type triplets based on mutant data.
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