Question

On average how often would you expect a restriction enzyme with a four base pair recognition site, such as TCGA to cut within a random DNA sequence?

Answer 1

Well, assuming that you have a protein with an average of 300 amino acids (which is a rough estimate), then out of those 300, it would have to recognize a quad sequence.

Since you only have: A, T, C, and G.
The chances of finding, say, ACCT, may be relatively higher than finding one which finds a sequnce that matches 10+