Now try the opposite. Following is the sequence of amino acids coded by an mRNA. Predict the nucleotide sequence in the RNA: Met-Phe-Phe-Phe-Phe-Phe
The predicted nucleotide sequence in the RNA is AUG-UUU-UUU-UUU-UUU-UUU. AUG acts as the initiator codon and codes for Methionine (Met), while UUU codes for Phenylalanine (Phe) based on the universal genetic code mentioned.
However, one faces difficulty in predicting the exact sequence because the genetic code is degenerate. This means that some amino acids are coded by more than one codon. Therefore, while UUU codes for Phe, other codons could also code for the same amino acid, making it difficult to determine the precise original RNA sequence without more information.
Explanation
The student identifies AUG as the codon for Methionine and UUU for Phenylalanine directly from the provided text which states 'AUG has dual functions... It codes for Methionine' and 'UUU would code for Phenylalanine'. The answer then addresses the 'difficulty' prompt by referencing the 'degenerate' property of the genetic code listed in the salient features, which states that 'Some amino acids are coded by more than one codon'.
Solution Steps
Step 1: Identify the codon for the first amino acid, Methionine (Met), which is AUG (also the initiator codon).
Step 2: Identify the codon for Phenylalanine (Phe), which is explicitly stated as UUU in the text.
Step 3: Construct the preliminary sequence: AUG-UUU-UUU-UUU-UUU-UUU.
Step 4: Explain the difficulty in prediction using the property of degeneracy (some amino acids have multiple codons), meaning the specific Phe codon used in the original RNA cannot be determined with 100% certainty from the amino acid sequence alone.