Biology MCAT question, please help

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If anyone can please help me answer this questions with details explanation. Thank you. It has been a while since I took chemistry, biology, physics, or biochem.

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@Ad2b choice: A, B and C all have single point mutation.
The correct answer is A. It has something to do with palindrome (palindrome is a 4-6 bp)... When I read the explanation, I'm still confused. Was it because B and C are not palindrome? because they are not 4-6 BP long?
 
Ohhhhhhh wow, that's a really good question. I was trying to solve it by looking at which nucleotide was changing, whether we were going from purine->pyrimidine, whether we formed a stop codon or a frame shift, etc. I didn't even consider the Southern blot aspect...

Basically when you do a Southern Blot, you add restriction enzymes (also called endonucleases) to the DNA you're interested in. These cut it up into chunks at certain points, called restriction sites. Then, you put the chunks in a gel, apply an electric field, and see how far the chunks of DNA migrate. Smaller chunks will migrate farther down the gel.

Restriction sites are palindromic. The point mutation in A screws up the palindrome, which will prevent the restriction enzymes from binding. This will mean DNA fragments from sample A will be different sizes than the fragments in the other samples, and we'll be able to identify them that way. Here is a decent picture:

endonuclease2.gif
 
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Ohhhhhhh wow, that's a really good question. I was trying to solve it by looking at which nucleotide was changing, whether we were going from purine->pyrimidine, whether we formed a stop codon or a frame shift, etc. I didn't even consider the Southern blot aspect...

Basically when you do a Southern Blot, you add restriction enzymes (also called endonucleases) to the DNA you're interested in. These cut it up into chunks at certain points, called restriction sites. Then, you put the chunks in a gel, apply an electric field, and see how far the chunks of DNA migrate. Smaller chunks will migrate farther down the gel.

Restriction sites are palindromic. The point mutation in A screws up the palindrome, which will prevent the restriction enzymes from binding. This will mean DNA fragments from sample A will be different sizes than the fragments in the other samples, and we'll be able to identify them that way. Here is a decent picture:

endonuclease2.gif
Thank you, great explanation, and lovely pic too
 
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The answer stated that palendrome has to be 4-6 BP long.. the other answers are not 4-6BP. That's what I think, let me know if you have anything different.
Read carefully, it said that most palindromes are 4-6 BP long, not that they have to be. But that fact doesn't even come into play here. The point is that the 5-AAGCTT-3 palindrome is only disrupted in choice A.

Keep in mind that of course AAGCTT isn't itself a palindrome, but its complimentary DNA will read 3-TTCGAA-5 which is the same sequence just running in the opposite direction.
 
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