Because if an error is made during protein synthesis, the resultis at worst one bad protein. If an error is made during DNAreplication, that error will persist for the entire lifespan ofthat cell and be inherited by every daughter cell it produces.Should the error prove deleterious, the effects can be catastrophicfor the cell or the organism. For example, if an error occurs in aprotein coding segment of DNA, it is possible that every proteinthat locus generates will now be defective.