What Are Nucleic Acids?

Nucleic acids are large biological polymers that store, transmit, and express genetic information in every cell and in every virus. Two classes exist: deoxyribonucleic acid, which holds the hereditary instructions of an organism, and ribonucleic acid, which carries those instructions to the protein synthesis machinery and performs catalytic and regulatory work of its own. The National Human Genome Research Institute defines nucleic acids as biomolecules whose major function involves the storage and expression of genomic information, a description that covers both the archival role of DNA and the far more varied roles of RNA.

Friedrich Miescher isolated the substance he called nuclein from the nuclei of white blood cells in 1869, and the name reflects both its cellular location and its acidity, which comes from the phosphate groups along its backbone. Molecular biophysics treats nucleic acids as physical objects with measurable persistence length, torsional stiffness, and melting behavior, quantities that govern how they fold, bind proteins, and respond to force.

Chemical Structure

A nucleic acid is a linear chain of nucleotides, each built from three parts: a five-carbon sugar, a phosphate group, and a nitrogenous base. The sugar is deoxyribose in DNA and ribose in RNA, and the single hydroxyl group that distinguishes them accounts for much of the difference in chemical stability between the two. Phosphodiester bonds join the 3' carbon of one sugar to the 5' carbon of the next, producing a sugar-phosphate backbone with a defined direction. The bases are adenine, guanine, and cytosine in both polymers, with thymine in DNA and uracil in RNA. James Watson and Francis Crick published the double helix in 1953 in their Nature paper on the molecular structure of nucleic acids, showing that two antiparallel strands wind around a common axis with adenine pairing to thymine and guanine to cytosine through hydrogen bonds.

Information Storage and Expression

Base pairing is what makes nucleic acids an information system rather than merely a class of polymers. Because each strand specifies the sequence of its partner, replication can copy a genome faithfully, and the same complementarity lets a transcribed RNA record the sequence of a gene. Reference material such as the NCBI Bookshelf chapter on the structure and function of DNA traces how a nucleotide sequence is transcribed into messenger RNA and then translated into a chain of amino acids according to the genetic code. Transfer RNA and ribosomal RNA carry out translation itself, and classes including microRNA, small interfering RNA, and long noncoding RNA regulate which genes are expressed and when.

Structure Beyond the Double Helix

Nucleic acids adopt conformations well beyond canonical B-form DNA. A-form and Z-form helices appear under different hydration and sequence conditions, guanine-rich sequences fold into four-stranded G-quadruplexes, and RNA folds into hairpins, pseudoknots, and complex tertiary architectures that create catalytic sites. Ribozymes such as the ribosomal peptidyl transferase center demonstrate that RNA can act as an enzyme, which underpins the hypothesis that RNA preceded protein and DNA in early life. These folding properties also make nucleic acids a construction material: DNA origami exploits programmable base pairing to assemble defined nanoscale shapes.

Applications

Nucleic acids have applications across a wide range of disciplines, including:

• Clinical diagnostics based on polymerase chain reaction and high-throughput sequencing
• Messenger RNA and DNA vaccine platforms
• Gene editing systems including CRISPR-Cas and antisense oligonucleotide therapy
• Forensic identification and paternity testing
• Aptamer-based biosensors and molecular recognition elements
• DNA data storage and DNA nanotechnology
• Agricultural genomics and marker-assisted breeding
• Phylogenetics, population genetics, and ancient DNA studies