Central tolerance deletes self-reactive T- or B-cell clones before the cells are allowed to mature. occurs in the primary lymphoid organs

TLS Online TPP Program

#Id: 3216

#Unit 4. Cell Communication and Cell Signaling

Carcinogens

1. Environmental DNA-damaging agents

2.Prevent DNA damage from being repaired with high fidelity

TLS Online TPP Program

#Id: 3218

#Unit 4. Cell Communication and Cell Signaling

Chemical carcinogens classified into two general categories:
1. Direct-acting carcinogens
2. Indirect-acting carcinogens

TLS Online TPP Program

#Id: 3220

#Unit 4. Cell Communication and Cell Signaling

Direct-acting carcinogens

Highly reactive compounds that can react with and modify nucleotide bases in DNA so as to distort the normal pattern of base pairing

TLS Online TPP Program

#Id: 3221

#Unit 4. Cell Communication and Cell Signaling

Direct-carcinogens includes:

Ethylmethane sulfonate (EMS)
Dimethyl sulfate (DMS)
Nitrogen mustards

TLS Online TPP Program

#Id: 3223

#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: 3225

#Unit 4. Cell Communication and Cell Signaling

Benzo(a)pyrene, found in cigarette smoke as well as in coal tar, undergoes metabolic activation by cytochrome P-450 in the lungs to form a potent mutagen.