One mechanism by which the activity of the replication origin is controlled is DNA methylation. 

TLS Online TPP Program

#Id: 10434

#Unit 4. Cell Communication and Cell Signaling

Direct-acting carcinogens

highly reactive compounds that can react with and modify nucleotide bases in DNA, to distort the normal pattern of base pairing.

TLS Online TPP Program

#Id: 10435

#Unit 4. Cell Communication and Cell Signaling

Direct-carcinogens includes:

Ethylmethane sulfonate (EMS)

Dimethyl sulfate (DMS)

Nitrogen mustards

TLS Online TPP Program

#Id: 10436

#Unit 4. Cell Communication and Cell Signaling

Indirect-acting carcinogens 

Relatively unreactive compounds that become modified to more reactive forms by cellular cytochrome P-450 enzymes

TLS Online TPP Program

#Id: 10437

#Unit 4. Cell Communication and Cell Signaling

Benzo(a)pyrene

(found in cigarette smoke & coal tar) undergoes metabolic activation by cytochrome P-450 in the lungs to form a potent mutagen

TLS Online TPP Program

#Id: 10438

#Unit 4. Cell Communication and Cell Signaling

P-450 enzymes, modify benzo(a)pyrene in a series of reactions, producing 7,8-diol-9,10-epoxide, a highly potent mutagenic species

TLS Online TPP Program

#Id: 10439

#Unit 4. Cell Communication and Cell Signaling