Question

Will restriction sites for an enzyme that has 4 bp in its restriction site be closer together, farther apart, or similarly spaced, on average, compared with those of an enzyme that has 6 bp in its restriction site? Explain your reasoning.

Answer 1

Restriction sites for a 4 bp enzyme will be closer together compared to a 6 bp enzyme because shorter sequences occur more frequently by chance in DNA; there are fewer possible combinations for 4 bp sequences than there are for 6 bp sequences.

Step-by-step explanation:

Restriction sites for an enzyme that has a 4 bp restriction site will generally be closer together on average compared with those of an enzyme that has a 6 bp restriction site. This is because the probability of a specific sequence occurring by chance in DNA increases with shorter sequences. The DNA sequence in the genome is very long, so a shorter sequence like one that is 4 nucleotides long will occur more frequently by chance than a longer 6 nucleotide sequence.

Given that the number of possible sequences for a 4 bp restriction site is 4^4 (=256 possibilities) and for a 6 bp restriction site is 4^6 (=4096 possibilities), it is statistically more likely to find a 4 bp site in a shorter DNA span than a 6 bp site. Therefore, on average, the restriction sites for 4 bp enzymes would be more frequent, and thus closer together, than those for 6 bp enzymes.