nucleici

Nucleici, or nucleic acids, are biopolymers that store, transmit, and express genetic information essential for life. The two main types are DNA (deoxyribonucleic acid) and RNA (ribonucleic acid). Both are polynucleotides made from nucleotides, each containing a sugar (deoxyribose in DNA, ribose in RNA), a phosphate group, and a nitrogenous base (adenine, cytosine, guanine, and thymine in DNA; adenine, cytosine, guanine, and uracil in RNA). Nucleotides are linked by phosphodiester bonds, forming long chains with a sugar-phosphate backbone and exposed bases.

DNA typically forms a double helix consisting of two antiparallel strands. Base pairing between adenine and thymine (A–T) or adenine and uracil (A–U) in RNA, and between cytosine and guanine (C–G), enforces a stable, complementary structure. The sequence of bases encodes genetic information. RNA is usually single-stranded and can fold into complex secondary structures; some viruses have RNA genomes that act as genetic material.

Functions of nucleic acids include storage of genetic information, faithful replication to pass hereditary material to progeny, and transcription of DNA into RNA. RNA molecules participate directly in protein synthesis (mRNA, tRNA, rRNA) and can have regulatory or catalytic roles, with many other RNA types identified in various cellular processes.

Nucleic acids are found in all living organisms and many viruses. They reside in the nucleus and organelles of eukaryotes, and in the cytoplasm or nucleoid regions of prokaryotes. They are subject to repair mechanisms to maintain integrity, and mutations in their sequences can have diverse biological consequences.

Historically, the chemical nature of nucleic acids and their structure were elucidated in the 20th century, culminating in the elucidation of the DNA double helix in 1953. Nucleic acids remain central to genetics, molecular biology, and biotechnology.