The following is the sequence of bases in the sense strand of a DNA segment and contains the beginning of a gene. DNA 3' A T A T T A C C A G G C A T G G A C C C C C G G G 5'
Based on this sequence, write the sequence of the anti-sense DNA strand and the mRNA. Label the 5' and 3' ends in your predicted sequences. The start codon in this organism is AUG. Indicate where the start codon is in your sequence. Why is the start codon important? Why does there have to be a specific start codon?
What will be an ideal response?
Answer:
Anti-Sense: 5' T A T T T A G G T C C G T A C C T G G G G G C C C 3'
mRNA: 5' U A U A A U G G U C C G U A C C U G G G G G C C C 3'
The start codon is bolded and underlined above and should only be indicated in the mRNA molecule. A start codon is important because it tells the ribosome where to start reading the codons so that the gene is read in the correct frame. Without a start signal (codon) to indicate which nucleotide to start reading the three letter codons from, the frame could be shifted. This would completely change the amino acids that are read and could result in "nonsense," or a non-functional protein.
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