Campbell Biology (10th Edition)

Published by Pearson
ISBN 10: 0321775651
ISBN 13: 978-0-32177-565-8

Chapter 17 - 17.1 - Concept Check - Page 340: 4


mRNA sequence: 5'-UGCUGACUU-3' Translated Amino Acid Sequence: Cys-"Stop"-Leu Prediction of Protein Function: The synthesized protein will not function all all, due to the "stop" codon that occurs in the middle of the amino acid sequence, which will sever the protein at that location.

Work Step by Step

First, we must transcribe the template strand sequence in order to find the sequence of the non-template strand. Since the template strand had the sequence 3'-TTCAGTCGT-5', we remember that A pairs with T and G pairs with C to transcribe to the contemplate strand, coming up with: 5'-AAGTCAGCA-3'. Second, in order to find our mRNA sequence, we will simply transcribe the non-template sequence we have just found, but replacing all T's with U's, since mRNA contains uracil instead of thymine. The resulting sequence will be 3'-UUCAGUCGU-5', or 5'-UGCUGACUU-3' if flipped to have the 5' side at the beginning. Finally, we will translate the mRNA sequence into a sequence of amino acids by first chunking each group of three letters into codons (5'-UGC / UGA / CUU-3'), and then using the amino acid chart to find the amino acid that correlates with each codon. UGC codes for Cys, UGA codes for "stop" and CUU codes for Leu. The resulting sequence is Cys-"Stop"-Leu. We now can see that a "stop" codon will occur in the middle of the sequence, which triggers the premature release of the amino acid sequence before all amino acids are attached. With this knowledge, we know that the protein sequence will not function at all like the protein derived from the template strand of DNA, because the amino acid chain is cut at this "stop" codon.
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