Given the polynucleotide sequence AUGCCGC, can you tell which is the 5' end?
A) There is no difference between the 5' and 3' ends of a single strand of DNA.
B) Counting the number of hydrogen bonds between the nitrogenous bases provides sufficient information to determine the 5' end.
C) No, you cannot tell without the sequence of the complementary strand.
D) No, unless you know the position of the phosphate group, you cannot differentiate the 3' end from the 5' end.
E) Yes, the 5' end begins with the start codon AUG.
IMAT 2023 · Question 30
Q30 - Structure of DNA and RNA
Pinned
The correct answer is D) No, unless you know the position of the phosphate group, you cannot differentiate the 3' end from the 5' end.
A strand has a 5' end (free phosphate) and a 3' end (free –OH). A string of letters like AUGCCGC only tells you the bases, not which end is which.
E is the tempting one: AUG is the start codon, but only when read 5'→3'. Seeing AUG at one end of a written sequence doesn't prove that end is 5', because the sequence could have been written in either direction.
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