Describe the differences between direct-acting and indirect-acting carcinogens.

Direct-acting carcinogens have reactive electrophiles that react with nitrogen and oxygen atoms in DNA.These modified nucleotides distort the normal pattern of base pairing.Indirect-acting carcinogens are generally unreactive,water-insoluble compounds.These compounds must first be converted to ultimate carcinogens by the introduction of electrophilic centers,usually by cytochrome P-450 enzymes in the liver.