chainterminating

Chainterminating describes processes that halt the growth of a polymer chain or nucleic acid synthesis by deactivating the active chain end. The term is used across polymer chemistry, biochemistry, and molecular biology, referring either to reagents deliberately added to cap chain ends or to natural termination events.

In polymerization, chain termination occurs when reactive chain ends are quenched by termination reactions such as combination or disproportionation of growing radicals, or by chain-terminating agents that scavenge radicals. These terminators cap the chain with a stable end group and stop further growth. In some systems, chain transfer agents or inhibitors are used to control molecular weight by terminating one chain and initiating another.

In DNA sequencing, chain-terminating nucleotides (such as dideoxynucleotides used in Sanger sequencing) are used to produce fragments that terminate when a single base is added, yielding a ladder of lengths used to read the sequence.

In pharmacology and virology, chain-terminating nucleoside analogs, such as certain antiviral drugs, are incorporated into nucleic acid chains and prevent further elongation, thereby blocking replication.

See also: chain reaction, termination (genetics).