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-His
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Use this information to answer the following questions:
The wild-type RNA consists of nine triplets. What is the role of the ninth triplet?

Verified step by step guidance

1. Step 1: Understand that the wild-type protein sequence is composed of eight amino acids, but the RNA has nine triplets (codons). Each codon corresponds to one amino acid or a special signal during translation.
2. Step 2: Recall that the last codon in an mRNA sequence often does not code for an amino acid but instead serves as a stop codon, signaling the end of translation.
3. Step 3: Identify that the ninth triplet in the wild-type RNA likely functions as a stop codon, which terminates protein synthesis and ensures the protein is the correct length.
4. Step 4: Compare the mutant sequences to see if any changes affect the length or composition of the protein, which can help confirm the role of the ninth triplet as a stop signal.
5. Step 5: Conclude that the ninth triplet's role is to act as a termination signal (stop codon) in the mRNA, preventing further addition of amino acids beyond the eighth residue.

Key Concepts

Genetic Code and Codons

The genetic code consists of triplets of nucleotides called codons, each specifying a particular amino acid or a stop signal during protein synthesis. Understanding how codons translate into amino acids is essential for interpreting RNA sequences and their corresponding protein products.

Stop Codons and Termination of Translation

Stop codons are specific triplets in mRNA (UAA, UAG, UGA) that do not code for amino acids but signal the end of translation. The ninth triplet in the wild-type RNA likely functions as a stop codon, terminating protein synthesis and defining the protein's length.

Effects of Mutations on Protein Sequence

Mutations can alter the amino acid sequence by changing codons, causing premature stops or extensions. Comparing wild-type and mutant sequences helps identify the role of specific codons, such as how the absence or change of the ninth triplet affects protein length and function.