How do bacteria protect their own DNA from restriction enzymes?

Correct answer: By methylation

The direct answer is option B: methylation. Restriction enzymes recognise particular DNA sequences and cut DNA at or near those recognition sites. Bacteria possess restriction-modification systems. Their own DNA is modified by adding methyl groups to suitable bases at the recognition sequences. This methylation acts like a chemical identity mark, so the restriction enzyme does not cut the bacterium’s protected DNA. DNA entering from outside may lack the correct methylation pattern and can therefore be recognised and cut. Option A, always breaking their own DNA, would destroy essential genetic information and cannot be a protection method. Option B is correct because methylation protects bacterial DNA from its matching restriction enzyme. Option C, oxidation, is not the standard protective modification in this system. Option D, glycolysis, is a metabolic pathway that breaks down glucose to release energy; it has no role in marking DNA for restriction protection. A useful qualification is that protection is carried out by specific modification enzymes and the exact patterns vary, but methylation is the expected school-level answer. Memory cue: restriction enzyme cuts foreign DNA; methyltransferase marks self DNA.