Restriction Endonuclease Question

[greenseeking]

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Hi, I have a question on a restriction endonuclase question on The Berkeley Review.

Please see the attached image for Question and Answer Choices.
Question says: Various combinations of restriction endonucleases are used to digest a length of DNA. Based on the DNA fragment patterns in the gel shown above, which of the following restriction maps BEST represent the length of bacterial DNA?

I thought I understood endonucleases but I don't... ALL of the answer choices make sense to me. For example, ECO RI has 5kb and 4 kb fragments and all the answer choices have a variation of 5 and 4 kb fragments.

 

[cloak25]

Bgl II has a 2kb and a 7kb fragment. only choice B shows this. is it B?

 

[greenseeking]

Hi, yes it's B...

Whoa how did you figure this out?? How did you know to look for the BglII fragments first? What if you looked at Eco RI or PstI?

Thanks.

 

[silverlion]

there are many ways of doing this....Using process of elimination you know that the answer cant be D as the EcoRI fragments would be 2 and 7 which is not the case on the gel. Pst1 is not a good candidate cause all of the rest (A, B and C) have the same size fragments for it...

As soon as you look at Bgl1 the answer is clear....

Don't try to find shortcuts for this...Take your time and if you are relaxed while doing these it wont take that long...

 

[Whiteshoes]

there are many ways of doing this....Using process of elimination you know that the answer cant be D as the EcoRI fragments would be 2 and 7 which is not the case on the gel. Pst1 is not a good candidate cause all of the rest (A, B and C) have the same size fragments for it...

As soon as you look at Bgl1 the answer is clear....

Don't try to find shortcuts for this...Take your time and if you are relaxed while doing these it wont take that long...

Could someone help elaborate on how to interpret the answer choices.
What does the 1 3 3 2 mean at the bottom each ans choice? I know by looking at the image Bg11 breaks up that DNA at 2kb & 7kb but how do the answer choices reflect that.

Thanks!

 

[cloak25]

In choice B, look at where the Bgl II cuts. There's only one cut so it splits the DNA into 2 smaller fragments, 2 and 7kb. In other words, to the right of the cut, its the 2kb fragment. To the left, its 1 + 3 + 3 = 7kb.

 

[ThirdEye]

Could someone help elaborate on how to interpret the answer choices.
What does the 1 3 3 2 mean at the bottom each ans choice? I know by looking at the image Bg11 breaks up that DNA at 2kb & 7kb but how do the answer choices reflect that.

Thanks!

Sum the length on each side.

Choice A would suggest 1kd and 8kd(3+3+2=8) for bgl II, so it's wrong because the gel shows 2kd and 7kd.
Choice B suggests 2 and 7, which is correct, so you just have to test the other ones and they turn out correct too.

 

[bleach121]

Sum the length on each side.

Choice A would suggest 1kd and 8kd(3+3+2=8) for bgl II, so it's wrong because the gel shows 2kd and 7kd.
Choice B suggests 2 and 7, which is correct, so you just have to test the other ones and they turn out correct too.

I know that bgl II fragments the dna in to 7kb and 2kb, but looking at answer choice B, it shows BOTH bgl II and Pst I. bgl II by itself isn't even on answer choice B. So how can you use the information for bgl II when its not on the answer choice?