According to the rules of the genetic code, there are six different reading fram

Question

According to the rules of the genetic code, there are six different reading frames in a double-stranded DNA molecule. One DNA strand serves as a template for transcription, which is complementary and antiparallel to the RNA product. The other DNA strand is the coding strand, which is identical in sequence to the RNA except for the substitution of uracil for thymine bases. A) There is a single open-reading frame (ORF) in the DNA molecule shown below. [Recall that an ORF begins with a start codon and ends with a stop codon.] Find the ORF in one of the DNA strands. Draw a box around the ORF in its coding strand. 5'-CGATCGCTATAAGGTTGACCTAGAGTTCGATTTACTCGTTTATGTGGCAGGCCATTTCTAAA-3' 3'-GCTAGCGATATTCCAACTGGATCTCAAGCTAAATGAGCAAATACACCGTCCGGTAAAGATTT-5' B) Translate the ORF into a protein sequence. [In the space provided below, write the protein's sequence. Use single-letter abbreviations for the amino acid residues.] (N-terminus)- _______________ -(C-terminus)

Explanation / Answer

A. The open reading frame in coding strand (coding strand is always shown as upper strand and in 5' to 3' direction in a DNA strand) will be as follow: bold and underlined.

5'-CGATCGCTATAAGGTTGACCTAGAGTTCGATTTACTCGTTTATGTGGCAGGCCATTTCTAAA-3'

Note: The RNA transcript synthesize in 5' to 3' direction and complimentry to the template strand (lower one). Here ATG (AUG in RNA) is starting codon and TAG (UAG in RNA) is terminating codon. Hence the ORF will be as shown in bold and underlined above.

B. The protein sequence will be as follows:

S-S-I-T-S-P-M (Ser-Ser-Ile-Tyr-Ser-Phe-Met)

Note: ATG is starting codon and codes for methionine. TAG is terminating codon and does not code for any amino acid.

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