EcoR I ........ 5'-GAATCC-3'
BamH I ....... 5'-GGATCC-3'
Hind III........ 5'-AAGCTT-3'

The enzyme BamHI recognizes a palindromic sequence and leaves one strand longer than the other. A piece of DNA is cleaved by BahM I. What does the end of the DNA look like?

A. ...GATCC-3'

B. ...C-3'

C. ...G-3'

D. ...G-3'

E. ...CTAGG-3'

I understood that one strand should be longer than the other, that's why I eliminated the "C" and "E" answer choices.

Then, I thought the answer choice is the "A" one. The first strand is similar to that in the data in the task, while the second is palindromic to it.

But this answer choice is incorrect. Then, I chose the "B" one. I thought: if we are given the sequence 5'-GGATCC-3', then the sequence 3'-GGATCC-5' is palindromic to it. (In this case, we have different letters near each number. That probably means they are vise versa versions of one another.)

It turned out the correct answer choice is the "D" one. I found such an explanation:

The end of the DNA cleaved by BamH I is complementary to the recognition site sequence shown in the table. One strand must also be longer than the other. The sequence CCTAG-5' is complementary to GATCC-3'.

But I can't understand this explanation... Please tell me what I do wrong..


1 Answer 1


Here is a quick drawing of how BamHI cuts the DNA: enter image description here

As you can see, after cutting, the two ends are actually the same (always read sequences from 5' to 3').


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