The binding of insulin is communicated through the single TM helix of each beta subunit to the paired Tyr kinase domains inside the cell, activating them to phosphorylate each other on three Tyr residues (Tyr1158, Tyr1162, Tyr1163)

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.

TLS Online TPP Program

#Id: 3267

#Unit 3. Fundamental Processes

Bruce Ames of the University of California at Berkeley devised a simple test for the potential carcinogenic effects of chemicals based on their capacity to cause mutations in the bacterium Salmonella typhimurium.