Hi, i have another question which i need help with.

 

Bacteriophage DNA is 48000 base pairs long. Hae III cuts it into 206 peices. Hind III cuts it in 7 places, whilst another 6-cutter Pst I cuts it into 28 peices. Why the diffrence?

 

I am thinking is this because they are specific ? as in 6-cutter, 4-cutter etc?

or is it something to do with DNA sequences?

 

Restriction enzymes cut at a specific DNA sequence.

Technically only type II restriction enzymes (as the one mentioned in the OP) cut at specific sites. But in direct to the question, yes it is because of the fact that the recognition length differs. A 4bp recognition sequence is likely to be more abundant in any given sequence than a 6 bp sequence. Unless of course that for some reason the sequence is devoid of any recognition sites (which is often the case in artificial DNA molecules). But in any random fragment the amount of potential sites scales inversely with the length of the recognition sequence.

Thank you i am sure about this now.