What are plasmids primarily classified as?

Plasmids are primarily classified as small extra DNA molecules that exist independently of the chromosomal DNA within a cell. They are typically circular and composed of double-stranded DNA. Plasmids are most commonly found in prokaryotes, such as bacteria, where they can carry genes that provide advantageous traits, such as antibiotic resistance. Due to their size and circular structure, they can replicate independently of the bacterial chromosome, which allows for easy transfer of genetic material between bacteria through processes like conjugation.

This classification as small extra DNA molecules emphasizes their distinctive role apart from the main genetic material of the organism. Their size and ability to carry additional genes make them important tools in molecular biology, including genetic engineering and cloning.