Singlestrand

Singlestrand refers to a single polymer chain, most often a nucleic acid, that is not paired with a complementary strand to form a double helix. In biology, single-stranded DNA (ssDNA) and single-stranded RNA (ssRNA) occur as transient intermediates during replication and transcription, and in many viruses whose genomes consist of a single nucleic acid strand. Single strands can fold back on themselves to form secondary structures through intramolecular base pairing, influencing stability, replication, and regulation.

Proteins such as single-stranded DNA binding proteins (SSB) and replication protein A stabilize exposed single-stranded regions during replication and repair. In laboratory techniques, denaturation and hybridization exploit single-stranded states, and many sequencing and cloning workflows begin with single-stranded templates. Sanger sequencing and several strand-specific assays rely on single-stranded DNA or RNA templates.

Single-strand oligonucleotides are used therapeutically and diagnostically, including antisense oligonucleotides and aptamers. A legacy method for polymorphism detection is single-strand conformation polymorphism (SSCP), which separates single-stranded DNA by conformation.

Genomes of certain viruses are single-stranded, notably ssRNA and ssDNA viruses, which include many plant and animal pathogens as well as parvoviruses and some picornaviruses. Handling ss nucleic acids requires care to avoid nuclease degradation and to accommodate their tendency to form structures that complicate analysis.