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A level biology recombinant dna question please help asap

Enzyme z (restriction endonuclease) recognises a particular sequence of bases in a gene. How many times does this sequence appear in the dna of this gene?

Why is the answer 5
Original post by ligays99999
Enzyme z (restriction endonuclease) recognises a particular sequence of bases in a gene. How many times does this sequence appear in the dna of this gene?

Why is the answer 5


Do you have the DNA sequence? I think we need more information? I think i might have done this past paper, can you give a screenshot?
do you have a link to the whole question from the exam paper or is that the whole question?
Original post by ProbablyJade
Do you have the DNA sequence? I think we need more information? I think i might have done this past paper, can you give a screenshot?


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Original post by ligays99999
Enzyme z (restriction endonuclease) recognises a particular sequence of bases in a gene. How many times does this sequence appear in the dna of this gene?

Why is the answer 5


There are 6 fragments of DNA. Meaning the initial DNA strand would have needed to be cut 5 times to produce 6 'parts'

The 'particular sequence of bases in a gene' is where the palindromic sequences are. Restriction endonucleases recognise these sequences and 'cut' the DNA at that specific site. SO there would be 5 palindromic sequences in the strand of DNA , so the restriction endonuclease can cut at each sequence to produce the 6 parts.

Hope this helped !
Original post by _evierose
There are 6 fragments of DNA. Meaning the initial DNA strand would have needed to be cut 5 times to produce 6 'parts'

The 'particular sequence of bases in a gene' is where the palindromic sequences are. Restriction endonucleases recognise these sequences and 'cut' the DNA at that specific site. SO there would be 5 palindromic sequences in the strand of DNA , so the restriction endonuclease can cut at each sequence to produce the 6 parts.

Hope this helped !


Yep! This is exactly right. If you can't picture it in your head, go grab a piece of string and cut it five times, you end up with 6 pieces of string (DNA). A restriction endonuclease will only bind and cut at a particular sequence so this exact sequence has to be repeated five times.
Original post by _evierose
There are 6 fragments of DNA. Meaning the initial DNA strand would have needed to be cut 5 times to produce 6 'parts'

The 'particular sequence of bases in a gene' is where the palindromic sequences are. Restriction endonucleases recognise these sequences and 'cut' the DNA at that specific site. SO there would be 5 palindromic sequences in the strand of DNA , so the restriction endonuclease can cut at each sequence to produce the 6 parts.

Hope this helped !


I remember this practice question, even the teacher didn't get why it wasn't 6. I think we kept counting the space between the S and the first fragment . But now that I think about it, if you stop focusing on the diagram, it makes more sense. This is why I hate sciences -.-
thanks for this!!
Original post by _evierose
There are 6 fragments of DNA. Meaning the initial DNA strand would have needed to be cut 5 times to produce 6 'parts'

The 'particular sequence of bases in a gene' is where the palindromic sequences are. Restriction endonucleases recognise these sequences and 'cut' the DNA at that specific site. SO there would be 5 palindromic sequences in the strand of DNA , so the restriction endonuclease can cut at each sequence to produce the 6 parts.

Hope this helped !


Thank you so much ! XXX
Original post by probablyjade
yep! This is exactly right. If you can't picture it in your head, go grab a piece of string and cut it five times, you end up with 6 pieces of string (dna). A restriction endonuclease will only bind and cut at a particular sequence so this exact sequence has to be repeated five times.


thanks for you help!!! <3
I'm doing that question right now. Basically since there is 6 fragments, the DNA must have been cut in 5 places by the restriction endonuclease.

- A level Biology student

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