If following is the sequence of nucleotides in mRNA, predict the sequence of amino acid coded by it (take help of the checkerboard): - AUG UUU UUC UUC UUU UUU UUC-
The sequence of amino acids coded by the given mRNA is: Methionine-Phenylalanine-Phenylalanine-Phenylalanine-Phenylalanine-Phenylalanine-Phenylalanine (Met-Phe-Phe-Phe-Phe-Phe-Phe).
Decoding:
- AUG codes for Methionine (Met) – it acts as the initiator codon and codes for Methionine.
- UUU codes for Phenylalanine (Phe) – as stated, from bacteria to human UUU codes for Phenylalanine.
- UUC also codes for Phenylalanine (Phe) – this demonstrates the degenerate nature of genetic code where some amino acids are coded by more than one codon.
The genetic code is read in mRNA in a contiguous fashion without punctuations, with each triplet codon specifying one amino acid.
Explanation
The question requires students to decode an mRNA sequence using the genetic code principles. AUG is the initiator codon coding for Methionine. UUU explicitly codes for Phenylalanine as mentioned in the context. UUC also codes for Phenylalanine, illustrating the degenerate property of the genetic code where multiple codons can code for the same amino acid. The context also includes a reverse exercise asking students to predict the nucleotide sequence from Met-Phe-Phe-Phe-Phe-Phe, where students would face difficulty because both UUU and UUC can code for Phe (degeneracy), making it impossible to determine the exact codon sequence uniquely.
Solution Steps
Step 1: Identify that AUG is the initiator codon coding for Methionine (Met)
Step 2: Decode UUU as Phenylalanine (Phe) based on the universal code principle
Step 3: Decode UUC as Phenylalanine (Phe) using the checkerboard/degenerate code property
Step 4: Read all 7 codons contiguously without punctuation to get the complete polypeptide chain