When mitotic chromosomes are subjected to proteolytic enzyme (trypsin) treatment followed by staining with the chemical dye Giemsa, they generate distinct chromosome-specific patterns called G-bands.

p (short; after the French petit) or q (long; for queue, the French word for tail)

TLS Online TPP Program

#Id: 3258

#Unit 3. Fundamental Processes

Intercalating agents are flat molecules containing several polycyclic rings that bind to the equally flat purine or pyrimidine bases of DNA, just as the bases bind or stack with each other in the double helix

TLS Online TPP Program

#Id: 3259

#Unit 3. Fundamental Processes

 Ultraviolet light induces the formation of a cyclobutane ring between adjacent thymines

TLS Online TPP Program

#Id: 3261

#Unit 3. Fundamental Processes

g-radiation and X-rays (ionizing radiation) are particularly hazardous because they cause double-strand breaks in the DNA, which are difficult to repair. If left unrepaired, double-strand breaks can be lethal to a cell.

TLS Online TPP Program

#Id: 3263

#Unit 3. Fundamental Processes

DNA is also subject to attack from reactive oxygen species (e.g., O2- , H2O2, and OH†). These potent oxidizing agents are generated by ionizing radiation and by chemical agents that generate free radicals. Oxidation of guanine, for example, generates 7,8-dihydro-8-oxoguanine, or oxoG. 

TLS Online TPP Program

#Id: 3264

#Unit 3. Fundamental Processes

The oxoG adduct is highly mutagenic because it can base-pair with adenine as well as with cytosine. If it base-pairs with adenine during replication, it gives rise to a G:C to T:A transversion, which is one of the most common mutations found inhuman cancers.

TLS Online TPP Program

#Id: 3266

#Unit 3. Fundamental Processes

The carcinogenic effects of ionizing radiation and oxidizing agents are partly caused by free radicals that convert guanine to oxoG.