How may a restriction enzyme act on a methylated recognition site?

Correct answer: Cutting may be blocked or reduced

Direct answer: Option A, cutting may be blocked or reduced. A methyl group added to DNA bases can change the chemical environment around a restriction recognition site. For many restriction enzymes, methylation prevents the enzyme from binding correctly or cutting efficiently. Bacteria use restriction-modification systems: methylation can protect their own DNA, while foreign unmethylated DNA may be cut. This is not universal for every enzyme, so “may” is the accurate wording. Option A is correct. Option B, cutting always increases, is wrong because methylation commonly inhibits or reduces cutting. Option C, DNA becoming protein, is impossible by methylation; DNA and protein are different biological molecules. Option D, an enzyme becoming a vitamin, is unrelated and chemically incorrect. Memory cue: methyl marks can act like a “do not cut” sign, but check enzyme-specific exceptions.