Definition and Structure of DNA
DNA, or deoxyribonucleic acid, is a long polymer molecule that serves as the hereditary material in humans and almost all other organisms. It consists of two strands forming a double helix structure, discovered by James Watson and Francis Crick in 1953. Each strand is made up of a backbone of sugar (deoxyribose) and phosphate groups, with nitrogenous bases—adenine (A), thymine (T), cytosine (C), and guanine (G)—projecting inward and pairing specifically: A with T, and C with G.
How DNA Stores Genetic Information
DNA stores genetic information through the sequence of its nucleotide bases, analogous to a code in a book. The order of A, T, C, and G along the strand determines the instructions for building proteins and other molecules essential for life. Genes, segments of DNA, encode specific traits; for example, a sequence might instruct the production of enzymes for metabolism. This linear arrangement allows for vast combinations, with the human genome containing about 3 billion base pairs.
Practical Example: DNA in Protein Synthesis
Consider eye color inheritance: a gene on DNA codes for melanin production. During protein synthesis, the DNA sequence is transcribed into messenger RNA (mRNA), which is then translated by ribosomes into proteins. If the DNA sequence has a variation (allele) for brown eyes, it leads to more melanin, resulting in brown pigmentation. This illustrates how DNA's stored information directly influences physical traits through molecular processes.
Importance and Applications of DNA
DNA's role in storing genetic information is fundamental to heredity, evolution, and development, enabling organisms to pass traits across generations. In medicine, understanding DNA aids in diagnosing genetic disorders like cystic fibrosis and developing targeted therapies, such as gene editing with CRISPR. Applications extend to forensics for identifying individuals via DNA fingerprinting and agriculture for creating genetically modified crops resistant to pests.