Imat 2016 q(31)

Practice Question Solving
1

(This question has already been solved BUT this question is about why the answer is A instead of E)
The question asks for complementary bases of a DNA plamid cut with a single restriction enzyme.
The sticky end on the left is A-A-C-G-A, which normally gives a complementary sequence of T-T-G-C-T which is the correct answer in the text. BUT if we’re talking about a plasmid that has to be closed, why isn’t the correct sequence in the reverse order (TCGTT), because when you close the plasmid the outermost base pair goes to the innermost base pair on the opposite end (I’ve attached a picture for clarity, I added the numbers in blue to explain what I mean, why doesn’t 1 go with 1, 2 with 2, 3 with 3 etc.)

[Album] imgur.com

thank you SO MUCH

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2

Hi!

the trick is in the phrasing of the question

yes when you roll it the 5 is correctly positionned in blue
BUT!!! the question is asking “what are the bases in positions 1,2,3,4 and 5 RESPECTIVELY”
it’s not about how they are read it’s about what order they want us to give the answers
so position1=T ; position2=T ; position3=G etc

Also we have no idea which strand is 5’3’ and which is 3’5’
so we can’t assume the complementary DNA is read from right to left

Hope this helps!!

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