nucleic acid

Nucleic acids are macromolecules composed of repeating nucleotide units, each consisting of a nitrogenous base (purine: adenine, guanine; pyrimidine: cytosine, thymine/uracil), a pentose sugar (deoxyribose in DNA, ribose in RNA), and a phosphate group linked via phosphodiester bonds forming a sugar-phosphate backbone. DNA is typically double-stranded, forming Watson-Crick antiparallel helices stabilized by hydrogen bonding (A-T with 2 H-bonds, G-C with 3 H-bonds) and base stacking; it encodes genetic information in the sequence of bases organized into genes. RNA is usually single-stranded and includes several functional types: messenger RNA (mRNA) carries genetic code from DNA to ribosomes; transfer RNA (tRNA) delivers amino acids during translation; ribosomal RNA (rRNA) forms structural/catalytic core of ribosomes; and regulatory RNAs (miRNA, siRNA, lncRNA) modulate gene expression.

Clinically, nucleic acid structure underlies key processes: DNA replication (semiconservative, requires DNA polymerase, helicase, primase, ligase), transcription (RNA polymerase synthesizes mRNA from DNA template), and translation (ribosome-mediated protein synthesis using tRNA and mRNA). Mutations in nucleic acid sequences (point mutations, insertions, deletions, trinucleotide repeats) cause genetic diseases (e.g., sickle cell anemia, cystic fibrosis, Huntington disease). Nucleic acid analogs are exploited pharmacologically—nucleoside reverse transcriptase inhibitors (NRTIs) for HIV, antiviral guanosine analogs (acyclovir), and chemotherapeutic antimetabolites (5-fluorouracil, methotrexate) that disrupt DNA/RNA synthesis in rapidly dividing cells. Nucleic acid-based diagnostic techniques—PCR, sequencing, Southern/Northern blotting, and CRISPR gene editing—are essential in modern molecular diagnostics and research. Additionally, nucleic acids are targets/vectors in vaccines (mRNA vaccines) and gene therapy.