DNA
Deoxyribonucleic acid (DNA) is the double-stranded helical polymer that stores the genetic information of virtually all living organisms. It is composed of nucleotide monomers, each containing deoxyribose sugar, a phosphate group, and one of four nitrogenous bases: adenine (A), thymine (T), guanine (G), or cytosine (C), paired by complementary hydrogen bonds (A–T and G–C). The sequence of bases encodes instructions for building proteins and regulating cellular functions, passed faithfully to daughter cells through semiconservative replication.
Key Properties of DNA
| Property | Detail |
|---|---|
| Structure | Right-handed B-form double helix (most common in cells) |
| Helix diameter | ~2 nm |
| Base pair rise | 0.34 nm per base pair; 10.5 bp per turn |
| Base pairing | A–T (2 hydrogen bonds), G–C (3 hydrogen bonds) |
| Human genome size | ~3.2 billion base pairs; ~20,000–25,000 protein-coding genes |
| Replication mode | Semiconservative (each strand is template for new strand) |
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Related Terms
Gene
A gene is a specific sequence of DNA (or RNA in some viruses) that encodes the information required to produce a functional product, most commonly a protein or functional RNA molecule. Genes occupy defined loci on chromosomes and are the fundamental units of heredity, transmitted from parent to offspring. The modern molecular definition encompasses not only coding sequences (exons) but also regulatory elements such as promoters and enhancers that control when, where, and how much a gene is expressed.
Chromosome
A chromosome is a long, thread-like structure composed of DNA and associated histone proteins (chromatin) that carries genes in a linear sequence. In humans, the diploid somatic cells contain 46 chromosomes (23 pairs), with each chromosome harbouring thousands of genes. Chromosomes are visible under a light microscope during cell division and are essential for the accurate segregation of genetic material to daughter cells.
Cell Cycle
The cell cycle is the ordered sequence of events by which a cell grows, replicates its DNA, and divides into two daughter cells. It consists of interphase (G1, S, and G2 phases) and the mitotic phase (mitosis and cytokinesis). Precise regulation of the cell cycle through checkpoints is essential for normal development; dysregulation leads to cancer and other diseases.
Abbreviation of "deoxyribonucleic acid": "deoxy" (lacking an oxygen on the 2' carbon of ribose) + "ribo" (ribose sugar) + "nucleic" (from Latin "nucleus", kernel) + "acid". The structure was elucidated by Watson and Crick in 1953 using X-ray crystallography data from Rosalind Franklin.