When Pr molecules are exposed to red light, most of them absorb it and are converted to Pfr, but some of the Pfr also absorbs the red light and is converted back to Pr because both Pr and Pfr absorb red light. 

TLS Online TPP Program

#Id: 740

#Unit 3. Fundamental Processes

primer:template junction is most important substrate for new DNA synthesis

TLS Online TPP Program

#Id: 741

#Unit 3. Fundamental Processes

The primer is complementary to, but shorter than, the template and have growing 3’ prime terminus

TLS Online TPP Program

#Id: 742

#Unit 3. Fundamental Processes

The phosphodiester bond is formed in an SN2 reaction in which the hydroxyl group at the 3’ end of the primer strand attacks the a-phosphoryl group of the incoming nucleoside triphosphate.

TLS Online TPP Program

#Id: 743

#Unit 3. Fundamental Processes

TLS Online TPP Program

#Id: 744

#Unit 3. Fundamental Processes

free energy for this reaction is rather small (DG–3.5 kcal/mol).

TLS Online TPP Program

#Id: 745

#Unit 3. Fundamental Processes

Additional free energy for the formation of phosphodiester bond is provided by the rapid hydrolysis of the pyrophosphate into two phosphate groups by an enzyme known as pyrophosphatase: