One strand of a section of DNA isolated from E. coli reads: 5’-GTAGCCTACCCATAGG-
ID: 54864 • Letter: O
Question
One strand of a section of DNA isolated from E. coli reads:
5’-GTAGCCTACCCATAGG-3’
Suppose that an mRNA were transcribed using the complement of this DNA strand as the template. What would the sequence of the mRNA in this region be?
How many different peptides could potentially be made from this sequence of RNA? Would the same peptides be made if the other strand of the DNA served as the template for transcription?
What peptide would be made if translation started exactly at the 5’ end of the mRNA in part A? When rRNAAla leaves the ribosome, what tRNA will be bound next? When the amino group of alanine forms a peptide bond, what bonds, if any, are broken, and what happens to tRNAAla?
Explanation / Answer
a) The given DNA sequence is 5’-GTAGCCTACCCATAGG-3’. The complementary DNA sequence from which mRNA is made is 3’ CATCGGATGGGTATCC 5’. Therefore, mRNA made from above complementary sequence will be 5’-GUAGCCUACCCAUAGG-3’.
b) Theoretically speaking, 3 peptides can be made from the above sequence. mRNA can be read from G or U or A so that in each case the frame of codons is different
Case 1: mRNA can be read from G- the codons are GUA GCC UAC CCA UAG G (VAYP)
Case 2- mRNA can be read from U- the codons are G UAG CCU ACC CAU AGG(PTHR)
Case 3- mRNA can be read from A- the codons are GU AGC CUA CCC AUA GG (SLPI)
c) If the other strand is used for mRNA synthesis, the peptides formed will be different.
d) VAYP is formed if translation started exactly at the 5’ end of the mRNA in part A. When rRNAAla leaves the ribosome, tRNAtyr will be bound next. When the amino group of alanine forms a peptide bond, what bonds, tRNAAla is released from Acceptor site. The dissociation of tRNAAla results in breaking of hydrogen bonds between tRNA Ala and mRNA Ala.
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