31. Given below is a partial coding sequence of a gene:

5′.AATGGACGCATGTGTCGATGG-3′

Which one of the following polypeptides CANNOT be produced by transcription and translation of the above DNA sequence in any of the three possible reading frames?

(1) Asn-Gly-Arg-Met-Cyc-Arg-Trp

(2) Asn-Ala-Cys-Phe-Ser-His

(3) Met-Asp-Ala-Cys-Val-Asp

(4) Trp-Thr-His-Val-Ser-Met

Determining Which Polypeptide Cannot Be Produced from a Given DNA Sequence by Translation in Any Reading Frame

When analyzing a DNA sequence to predict possible polypeptides produced by transcription and translation, it is essential to consider all three possible reading frames on the coding strand. Each reading frame shifts the grouping of nucleotides into codons and thus affects the resulting amino acid sequence.

Given DNA Sequence (Coding Strand):

5’- AAT GGACGCATGTGTCGATGG -3’

Step 1: Identify the Three Possible Reading Frames

• Frame 1: Starts at nucleotide 1

• Frame 2: Starts at nucleotide 2

• Frame 3: Starts at nucleotide 3

Step 2: Transcribe DNA to mRNA

Since the given sequence is the coding strand (5’ to 3’), the mRNA sequence will be the same as the coding strand with thymine (T) replaced by uracil (U):

5’- AAU GGACGCAUGUGUCGAUGG -3’

Step 3: Divide mRNA into Codons for Each Frame

Frame 1 (starting at nucleotide 1):
AAU | GGA | CGC | AUG | UGU | CGA | UGG

• AAU = Asn

• GGA = Gly

• CGC = Arg

• AUG = Met

• UGU = Cys

• CGA = Arg

• UGG = Trp

Resulting peptide: Asn-Gly-Arg-Met-Cys-Arg-Trp

Frame 2 (starting at nucleotide 2):
A | AUG | GAC | GCA | UGU | GUC | GAU | GG…

• AUG = Met

• GAC = Asp

• GCA = Ala

• UGU = Cys

• GUC = Val

• GAU = Asp

Resulting peptide: Met-Asp-Ala-Cys-Val-Asp

Frame 3 (starting at nucleotide 3):
AA | UGG | ACG | CAU | GUG | UCG | AUG | G…

• UGG = Trp

• ACG = Thr

• CAU = His

• GUG = Val

• UCG = Ser

• AUG = Met

Resulting peptide: Trp-Thr-His-Val-Ser-Met

Step 4: Compare with Given Options

Explanation

• Option (2) includes amino acids Asn-Ala-Cys-Phe-Ser-His, which does not correspond to any of the three reading frames derived from the given DNA sequence.

• The other three options match exactly the peptide sequences translated from one of the three reading frames.

Keywords for SEO Optimization

• DNA translation reading frames

• Protein prediction from DNA sequence

• Open reading frame analysis

• Codon to amino acid translation

• Multiple reading frame translation

• Molecular biology of gene expression

• DNA to protein sequence conversion

• Genetic code and reading frames

• Peptide synthesis from DNA

• Translation frame shift effects

Conclusion

Among the given options, the polypeptide sequence Asn-Ala-Cys-Phe-Ser-His (Option 2) cannot be produced by transcription and translation of the DNA sequence 5’-AATGGACGCATGTGTCGATGG-3’ in any of the three possible reading frames.

Correct answer: (2) Asn-Ala-Cys-Phe-Ser-His