（A)AATT (B)ACTC (C)GGCC (D)ACCA
TTCC TCAG CCGG TGGT
- C CLv 61 decade agoBest Answer
The answer should be (B) GGCC.
A restriction enzyme (限制酶) cuts at a restriction site, which is generally palindromic (because restriction enzymes often works as homodimers). Among all the sequences listed, only GGCC is palindromic, which means they are the same if you read it from either direction:
5' - GGCC - 3'
3' - CCGG - 5'
So the bottom strand would also read GGCC (always read from 5' to 3').
2009-01-25 05:20:50 補充：
上排跟下排 represent the two strands of DNA, typically you assume the top strand is 5' to 3', the bottom strand is 3' to 5'
2009-01-25 05:22:44 補充：
(A)5' - AAGG - 3'
3' - TTCC - 5'
(B)5' - AGTC - 3'
3' - TCAG 5'
(C)5' - GGCC - 3'
3' - CCGG -5'
(D)5' - ACCA - 3'
3' - TGGT - 5'
(E)5' - AAAA - 3'
3' - TTTT -5'
Here it is still (C), only (C) is the same no matter which strand you read the sequence.
2009-01-25 05:24:13 補充：
So if you take option (E), if you read the sequence on top strand, it is AAAA, but if you read it from the bottom strand, it is TTTT. If you take (B), the top strand is AGTC, but the bottom strand is GACT (read from 5' to 3'). So they are not the same.
2009-01-25 05:24:46 補充：
-- that's right, in the original question option (B) is not even right, the top and bottom strands are not complimentary.
2009-01-25 20:43:09 補充：
Campbell is wrong. If it is AGCT, it would be right, but not AGTC.
Here's some examples of actual restriction sites:Source(s): I'm a graduate student in genetics.