DNA, or deoxyribonucleic acid, stands as the fundamental hereditary material in humans and virtually all other organisms. Remarkably, nearly every cell within an individual’s body houses the identical DNA blueprint. The vast majority of DNA resides within the cell’s nucleus, termed nuclear DNA. However, a small fraction exists in the mitochondria, known as mitochondrial DNA or mtDNA. Mitochondria are vital cellular components responsible for converting energy from food into a usable form for the cell.
The information encoded within DNA is structured as a code composed of four chemical bases: adenine (A), guanine (G), cytosine (C), and thymine (T). Human DNA encompasses approximately 3 billion of these bases, with over 99 percent exhibiting uniformity across individuals. The specific sequence, or order, of these bases dictates the instructions necessary for building and maintaining an organism. This is analogous to the way letters of the alphabet are arranged to form words and sentences, conveying meaning and direction.
These DNA bases engage in pairing, adenine (A) always pairing with thymine (T), and cytosine (C) with guanine (G), forming units known as base pairs. Each base is also linked to a sugar molecule and a phosphate molecule. The combination of a base, sugar, and phosphate is termed a nucleotide. Nucleotides are organized into two lengthy strands that intertwine to create a spiral structure called a double helix. Imagine a ladder twisted into a spiral; the base pairs constitute the rungs, while the sugar and phosphate molecules form the ladder’s vertical sides.
A crucial characteristic of DNA is its capacity to replicate, or create copies of itself. Each strand within the double helix can serve as a template for duplicating the base sequence. This replication process is essential during cell division, ensuring that each new cell receives an exact replica of the DNA present in the original cell, thus maintaining genetic continuity across generations.
Diagram illustrating DNA structure with base pairs and sugar-phosphate backbone
Credit: U.S. National Library of Medicine
