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Deoxyribonucleic acid (DNA) is the molecule nature uses to transmit genetic information from one generation to the next. Each species possesses a unique DNA sequence that defines its physical traits and influences behavior. These sequences are organized into chromosomes—twisted strands of DNA wrapped around proteins—within the cell nucleus.
DNA is a polymer of alternating sugar and phosphate units. Attached to each sugar is one of four nitrogenous bases—adenine, thymine, cytosine, or guanine. The specific order of these bases constitutes the genetic code that directs protein synthesis. Every cell in the human body carries 23 pairs of chromosomes, with one set inherited from each parent.
Two complementary DNA strands form the iconic double‑helix structure. Hydrogen bonds between paired bases stabilize the helix. Histone proteins bind to DNA to create chromatin, the material that compacts chromosomes to fit within the nucleus. Histones also protect DNA and regulate gene expression by influencing which chromosomal regions are active.
Genes occupy roughly 2% of the chromosomal landscape. The remaining 98% contains regulatory elements, structural DNA, and, in some regions, non‑coding sequences often referred to as “junk DNA.” Gene expression follows a two‑step process: transcription of DNA into messenger RNA (mRNA) and translation of mRNA into protein by ribosomes.
Before cell division, DNA must be faithfully replicated. Helicase enzymes unwind the double helix, and DNA polymerase synthesizes a new strand using each original strand as a template. Base‑pairing rules guarantee accurate copying. The duplicated chromosomes are then segregated into daughter cells through mitosis, followed by cytokinesis.
