In: Biology
What would be the predicted cutting frequency of a restriction enzyme that recognizes a 10-base recognition sequence?
a. 1048576
b. 10000
c. 0.00001
d. 4.0 E-10
e. 9.5 E-7
A is the answer
Just 4 to the power 10 is equal to 1048576
The frequency by which a Class II restriction enzyme will cut DNA is mainly a function of the length of the sequence it is sensitive to. For instance:
BsuRI has a recognition sequence of 4 base-pairs. Out of sheer probability, we see that with 4 positions, and each position having potentially 4 different values, there are 44 = 256 different possibilities for any given 4-base long strand. Therefore, theoretically (assuming completely random DNA), this enzyme will cut 1 in 256 4-base-pair long sites.
EcoRI, on the other hand, recognizes a sequence of 6 base-pairs. 46 = 4096 possible combinations with this length, and so EcoRI will cut 1 in 4096 6-base-pair long sites.
NotI has a recognition sequence of 8 base-pairs. 48 = 65536 possible combinations, and so NotI will theoretically cut one out of 65536 8-base-pair long sites.
As you can see, the frequency of cutting has much to do with the length of the sequence (because that is directly affected by probability). There is some effect from GC content, as well, but I need to further research that.