Problems on Protein Synthesis

If this sequence of bases represents the start of a gene on double-stranded DNA, what is the sequence of the transcribed RNA, what is its polarity, and what is the polarity of the DNA?

G C T A C G G A T T G C T GC G A T G C C T A A C G A C

Answer: Begin by writing the complementary strand to each DNA strand: C G A U G C C U A A C G A C for the top, and G C U A C G G A U U G C U G for the bottom. Now look for the start codon, AUG. It is present only in the RNA made from the top strand, so the top strand must have been transcribed. The polarity of the start codon is 5’-A U G-3’. Since transcription occurs 5’and 3’, and since nucleic acids are antiparallel, the left end of the top DNA strand is the 3’ end.

Given the following end part of a gene, which will be transcribed and then translated into a pentapeptide, provide the base sequence for its messenger RNA. Give the anticodons on the transfer RNAs by making use of wobble rules. What amino acids are incorporated? Draw the actual structure of the pentapeptide.

3’-TACAATGGCCCTTTTATC-5’5’-ATGTTACCGGGAAAATAG-3’

Part of a DNA strand to be transcribed has the followingsequence:3’-TACTAACTTACGCTCGCCTCA-5’a. What is the sequence of RNA transcribed fromthis part of the strand?b. What sequence of amino acids does the RNA produce?