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:
For each mutant protein, determine the specific ribonucleotide change that led to its synthesis.

검증된 단계별 안내

Step 1: Understand that each amino acid in a protein is encoded by a set of three nucleotides called a codon in the mRNA, which is transcribed from the DNA sequence. To find the ribonucleotide change, you need to compare the mutant amino acid sequence to the wild-type sequence and identify where the differences occur.

Step 2: For Mutant 1, note that the sequence is truncated after the second amino acid (Met-Trp). This suggests a premature stop codon appeared after the second codon. Identify the codon for the third amino acid in the wild-type (Tyr) and determine which single nucleotide change could convert it into a stop codon (UAA, UAG, or UGA).

Step 3: For Mutant 2, observe that the third amino acid is His instead of Tyr, while the rest of the sequence matches the wild-type. Find the codons for Tyr and His, then determine the single nucleotide substitution that changes the Tyr codon to a His codon.

Step 4: For Mutant 3, the entire sequence is different starting from the second amino acid. Compare each amino acid in Mutant 3 to the wild-type sequence and identify the codons for the new amino acids. This suggests multiple nucleotide changes or a frameshift mutation. Consider whether a single nucleotide change can explain the differences or if a more complex mutation occurred.

Step 5: Summarize the specific ribonucleotide changes by writing the original codon and the mutated codon for each affected amino acid, showing the exact nucleotide substitution(s) responsible for the mutant protein sequences.

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Genetic Code and Codon-Amino Acid Relationship

The genetic code consists of nucleotide triplets called codons, each specifying a particular amino acid. Understanding how codons translate into amino acids is essential to link changes in nucleotide sequences (mutations) to alterations in protein sequences. This relationship allows prediction of nucleotide changes from observed amino acid substitutions.

Types of Mutations and Their Effects on Protein Sequence

Mutations such as nonsense, missense, and frameshift mutations alter the nucleotide sequence and consequently the amino acid sequence. For example, a nonsense mutation introduces a premature stop codon, truncating the protein, while missense mutations substitute one amino acid for another. Recognizing these mutation types helps explain the differences between wild-type and mutant proteins.

Translation Termination and Its Impact on Protein Length

Translation stops when a stop codon (UAA, UAG, UGA) is encountered, resulting in protein termination. Mutations that create premature stop codons lead to shorter proteins, as seen in truncated mutants. Understanding how stop codons function is crucial to deducing which nucleotide changes cause early termination in mutant proteins.