The genetic code in DNA is defined by four chemical building blocks called nucleotides: adenine (A), thymine (T), cytosine (C), and guanine (G). The sequence of these bases along a DNA strand encodes the information needed to build proteins, via the intermediate molecule RNA. Specific groups of three nucleotides, called codons, specify individual amino acids—the basic units of proteins—and signals such as start and stop during translation. In RNA, thymine is replaced by uracil (U), and the codon-to-amino-acid correspondence is read by the cellular machinery (ribosomes) during protein synthesis. Key points:
- DNA is a double helix composed of two long strands, each made of alternating sugar-phosphate backbones and nucleotide units. The four bases pair specifically (A with T, C with G) to form the ladder-like structure, helping to preserve the genetic code across generations.
- Genes are specific segments of DNA whose sequence determines the order of amino acids in a protein. The process begins with transcription, producing messenger RNA (mRNA) that carries the code from DNA to ribosomes.
- Translation reads the mRNA codons in sets of three nucleotides. Each codon corresponds to an amino acid or a termination signal, dictating the final protein sequence.
- The genetic code is nearly universal across organisms, with some minor variations in certain mitochondria and microorganisms.
