Triplet states generally have much longer lives (take longer to de‐excite) than singlet states and are at a lower energy level.

TLS Online TPP Program

#Id: 3404

#Unit 3. Fundamental Processes

The LexA repressor is inactivated when it catalyzes its own cleavage at a specific Ala–Gly peptide bond.

TLS Online TPP Program

#Id: 3405

#Unit 3. Fundamental Processes

SOS response in E. coli: 

The LexA protein is the repressor in this system, which has an operator site near each gene. Because the RecA gene is not entirely repressed by the LexA repressor, the normal cell contains about 1,000 RecA monomers. 

TLS Online TPP Program

#Id: 3412

#Unit 3. Fundamental Processes

SOS response in E. coli:

When DNA is extensively damaged (such as by UV light), DNA replication is halted and the number of single-strand gaps in the DNA increases.

RecA protein binds to this damaged, single-stranded DNA, activating the protein’s co-protease activity.

While bound to DNA, the RecA protein facilitates cleavage and inactivation of the LexA repressor. When the repressor is inactivated, the SOS genes, including RecA, are induced;

TLS Online TPP Program

#Id: 3417

#Unit 3. Fundamental Processes

Alternative models for translesion synthesisIn; Two models explain the mechanism of translesion synthesis, each likely to be true under particular circumstances.

The polymerase-switching model,

The gap-filling model,

TLS Online TPP Program

#Id: 3418

#Unit 3. Fundamental Processes

NHEJ is a backup system in yeast, but in higher cells it is the principal pathway by which breaks are repaired.

TLS Online TPP Program

#Id: 3419

#Unit 3. Fundamental Processes

Ku70 and Ku80 are the most fundamental components of NHEJ. They constitute a heterodimer that binds to the DNA ends and recruits DNA-PKcs, which is a protein kinase