What is the main role of the modification part in a restriction-modification system?

Correct answer: Protecting self DNA by methylation

The modification part is the protective component of a restriction-modification system. It recognizes the organism’s own DNA and adds methyl groups to particular bases at the system’s recognition sites. This chemical marking does not destroy the DNA or change its information. Instead, it tells the restriction enzyme that this DNA belongs to the host and must be spared. Therefore, option A is correct. The other choices describe unrelated processes: coloring DNA is not a biological role here, making protein from RNA is translation, and changing sugar into fat is a metabolic process.

Restriction enzymes can cut DNA that lacks the protective methyl mark, including incoming foreign DNA. The modification enzyme acts before such cutting becomes a problem by methylating the host’s corresponding sites. Thus, methylation protects self DNA while allowing the restriction component to attack suitably unmodified foreign DNA. The wording “protecting self DNA by methylation” accurately states the main function, so the supplied answer is consistent.