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Our entire genetic blueprint is encoded in a remarkably simple four‑letter language. DNA, the polymer that stores this information, consists of a chain of nitrogenous bases attached to a sugar‑phosphate backbone and wound into a double helix. The sequence of bases is translated into the proteins and enzymes that perform every cellular function, a process celebrated for its elegance and precision.
DNA is built from adenine (A), guanine (G), cytosine (C), and thymine (T). When DNA is transcribed into messenger RNA (mRNA), thymine is swapped for uracil (U). Adenine and guanine belong to the purine class, while cytosine, thymine, and uracil belong to the pyrimidine class. These five letters—A, G, C, T, and U—constitute the entire genetic alphabet.
Replication and transcription require the double helix to unwind. Each base pairs with a complementary partner: A pairs with T (or U in RNA) via two hydrogen bonds, and C pairs with G via three hydrogen bonds. This strict pairing ensures an exact copy of the genetic code. Specialized enzymes, such as DNA helicase and RNA polymerase, orchestrate the unwinding and synthesis processes.
After transcription, the mRNA strand travels to the ribosome, the cell’s protein‑synthesizing factory. The ribosome reads the sequence in triplets—codons—each comprising three nucleotides. Codons signal the addition of specific amino acids to the growing polypeptide chain.
Twenty distinct amino acids form the building blocks of proteins. With 64 possible codon combinations, several amino acids are encoded by more than one codon—a phenomenon known as codon redundancy. Start codons (typically AUG) mark the beginning of translation, while stop codons (UAA, UAG, UGA) signal termination.
In humans, between 50,000 and 100,000 genes encode the proteins that give rise to our structure, function, and regulation. Each gene produces a single protein, which can fold into a functional three‑dimensional shape—either as a structural component or as an enzyme that catalyzes biochemical reactions.
