In polyacrylamide gel formation, what initiates the polymerization reaction in the chemical method?
Chemical polymerization of acrylamide and bisacrylamide requires free radical generation to initiate vinyl addition. Ammonium persulfate (APS) decomposes to produce sulfate free radicals that attack acrylamide double bonds, starting chain propagation. Tetramethylethylenediamine (TEMED) acts as a catalyst by accelerating APS decomposition and facilitating radical formation at room temperature, stabilizing the reaction and controlling gelation rate. Neither acts efficiently alone for rapid casting. Riboflavin initiates photochemical polymerization under UV light, not chemical initiation. Glycerol is a density agent. Thus APS-TEMED pair constitutes the standard chemical initiator system.
Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.