hypothetical question -- HELP!

[Bunsen Honeydew]

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can anyone shed some light on this hypothetical question that I don't understand?

question: DNA from e-coli & h. influenza are separated with restriction endonuclease EcoRI & fragments are separated on gel. Examination shows that hi DNA was cleaved into numerous frags while ecoli was not. Which best explains diff

A. methylation of ec
B meth of hi
C. obviously wrong answer
D. ditto
E. presence of transposons in ec DNA
F. presence of transposons in hi DNA

I would go with F b/c I think (thought) that this what EcoRI does -- cuts at the inverted repeats, but the answer is A (which I could understand in terms of hindering general transcription).

I'm sure someone's explanation will reveal the tragic & gaping hole in my general science background -- pls. help!!

 

[osli]

Methylation means inactive/non-transcribing DNA. It's likely that it would protect the DNA from the restriction enzymes.

The transposons answer doesn't really make sense, unless you knew that your restriction sequence was contained only on some given transposon and nowhere else. But that is just too contrived to be correct, as neither the stem or answers suggest that.

 

[butaloh666]

can anyone shed some light on this hypothetical question that I don't understand?

question: DNA from e-coli & h. influenza are separated with restriction endonuclease EcoRI & fragments are separated on gel. Examination shows that hi DNA was cleaved into numerous frags while ecoli was not. Which best explains diff

A. methylation of ec
B meth of hi
C. obviously wrong answer
D. ditto
E. presence of transposons in ec DNA
F. presence of transposons in hi DNA

I would go with F b/c I think (thought) that this what EcoRI does -- cuts at the inverted repeats, but the answer is A (which I could understand in terms of hindering general transcription).

I'm sure someone's explanation will reveal the tragic & gaping hole in my general science background -- pls. help!!

Methylated DNA (linked to deacetylation of histones) is tightly packed and so the endonuclease can't gain access to it. This also explains why genes within or near methylated DNA segments are not transcribed.