Why is low-salt clean DNA considered good in restriction digestion?

Correct answer: To keep enzyme activity better

The direct answer is option A: low-salt, clean DNA helps the restriction enzyme remain active and makes digestion more reliable. Restriction enzymes work in a carefully balanced reaction mixture. Excess salt can change ionic strength and may interfere with DNA binding, enzyme structure, or recognition of the restriction site. Other purification residues can also inhibit the enzyme. Therefore, clean DNA with little unwanted salt is a good starting material. Option A is correct because it supports consistent cutting and clearer gel results. Option B is wrong: restriction digestion does not convert DNA into protein. Option C is wrong because DNA does not stop a gel; the gel is the medium through which fragments move during electrophoresis. Option D is wrong because the enzyme is not methylated merely by using low-salt DNA; methylation is a separate chemical or biological modification and may affect some restriction enzymes. Low salt does not guarantee success by itself: the correct buffer, temperature, pH, DNA amount, and incubation time are also needed. Memory cue: clean and low-salt DNA lets the enzyme work without chemical interference.