林漢祥 asked in 科學生物學 · 1 decade ago

生物~生物技術概論~被限制酶所切割?

下列DNA序列何者最有可能被限制酶所切割?

(A)AATT (B)ACTC (C)GGCC (D)ACCA

TTCC TCAG CCGG TGGT

請幫我詳解

有校正過打字了

謝謝

Update:

我認為這題的(B)選項有誤

題目出這樣不知是什麼意思

上排跟下排有何關係呢??

Update 2:

下列哪一雙股DNA分子上的序列可以是某特殊限制酵素的識別位?

(A)AAGG

TTCC

(B)AGTC

TCAG

(C)GGCC

CCGG

(D)ACCA

TGGT

(E)AAAA

TTTT

跟這題有何不一樣呢?

Update 3:

但我補充的這題

是campbell上的題目

給的答案是(B)

1 Answer

Rating
  • C C
    Lv 6
    1 decade ago
    Best 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:

    我認為這題的(B)選項有誤

    -- 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:

    是campbell上的題目

    給的答案是(B)

    Campbell is wrong. If it is AGCT, it would be right, but not AGTC.

    Here's some examples of actual restriction sites:

    http://en.wikipedia.org/wiki/Palindromic_sequence

    Source(s): I'm a graduate student in genetics.
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