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DNA is a long polymer composed of repeating units called nucleotides. Each nucleotide contains one of four nitrogenous bases—adenine (A), thymine (T), cytosine (C), or guanine (G). The precise order of these bases along the DNA strand holds the instructions needed to build every protein in an organism.
Although DNA uses only four bases, it can specify 20 different amino acids that make up proteins. The key lies in the way the bases are read in groups of three—called codons or triplets. There are 64 possible codons (4³), and each one maps to a specific amino acid or a stop signal during translation.
For example, the codon ATG codes for methionine, the amino acid that starts every protein chain. Similarly, TTT encodes phenylalanine, while GGG encodes glycine. Some amino acids are represented by multiple codons, a feature known as the redundancy or degeneracy of the genetic code.
During transcription, a messenger RNA (mRNA) copy of the DNA sequence is produced. The ribosome then reads the mRNA codons, matching each to the corresponding amino acid via transfer RNA (tRNA). These amino acids are linked together, forming a polypeptide chain that folds into a functional protein.
In essence, the sequence of A, T, C, and G bases in DNA dictates the sequence of amino acids in proteins, demonstrating how a simple molecule can orchestrate the complex chemistry of life.
