Consider the following portion of mRNA produced by the normal order of DNA nucleotides:
5'CUU|AAA|CGA|GUU3'
e. What happens to the protein sequence if an A is added to the beginning of the chain and the sequence changes to 5'ACU|UAA|ACG|AGU3'?

Verified step by step guidance

1. Step 1: Understand the concept of the genetic code and how mRNA is translated into a protein sequence. Each group of three nucleotides (codon) in mRNA corresponds to a specific amino acid or a stop signal during translation.
2. Step 2: Analyze the original mRNA sequence (5'CUU|AAA|CGA|GUU3') and divide it into codons. These codons are: CUU, AAA, CGA, and GUU. Use a codon chart to determine the amino acids they encode.
3. Step 3: Examine the modified mRNA sequence (5'ACU|UAA|ACG|AGU3') after the addition of an A at the beginning. Divide this sequence into codons: ACU, UAA, ACG, and AGU. Note that the reading frame has shifted due to the insertion.
4. Step 4: Use a codon chart to decode the new sequence. Identify the amino acids corresponding to the new codons. Pay attention to UAA, which is a stop codon and signals the termination of translation.
5. Step 5: Compare the protein sequence produced by the original mRNA with the sequence produced by the modified mRNA. Discuss how the addition of an A at the beginning alters the reading frame, potentially leading to a truncated or completely different protein.

Key Concepts

mRNA Translation

mRNA translation is the process by which ribosomes synthesize proteins based on the sequence of nucleotides in mRNA. Each set of three nucleotides, known as a codon, corresponds to a specific amino acid. Understanding this process is crucial for analyzing how changes in the mRNA sequence can affect the resulting protein.

Codon Changes and Protein Structure

Codon changes in mRNA can lead to different amino acids being incorporated into a protein, potentially altering its structure and function. For instance, adding an 'A' at the beginning of the sequence shifts the reading frame, which can result in a completely different set of codons and thus a different protein product.

Frameshift Mutation

A frameshift mutation occurs when nucleotides are added or deleted from the DNA or RNA sequence, causing a shift in the reading frame. This type of mutation can drastically change the downstream amino acid sequence, often leading to nonfunctional proteins. In the given question, the addition of an 'A' creates a frameshift that alters the entire protein sequence.