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Deoxyribonucleic acid (DNA) is the genetic blueprint of all cellular life. While it stores the genetic instructions that define who we are, it is the proteins produced from these genes that perform the myriad functions essential for growth, development, and immune defense.
So, does DNA actually tell cells which proteins to build? The answer is both yes and no. DNA encodes the information, but the process of translating that information into functional proteins requires a series of carefully regulated steps.
The well‑established sequence of events—first transcribing DNA into messenger RNA (mRNA), then translating that mRNA at ribosomes to synthesize proteins—is known as the central dogma of genetics, a concept first articulated by Francis Crick in 1958.
DNA is composed of nucleotides, each consisting of a phosphate group, a deoxyribose sugar, and one of four nitrogenous bases: adenine (A), thymine (T), cytosine (C), or guanine (G). Base pairing follows strict rules—adenine always pairs with thymine, and cytosine always pairs with guanine—forming the familiar double‑helix structure.
Within this double helix, the sequence of bases encodes the instructions for proteins. A contiguous stretch of DNA that codes for a particular protein is called a gene.
Transcription begins when the enzyme RNA polymerase binds to a promoter region and reads the DNA template strand. It synthesizes a complementary strand of messenger RNA (mRNA), replacing thymine (T) with uracil (U). The nascent RNA strand is initially called pre‑mRNA.
In eukaryotic cells, pre‑mRNA undergoes extensive processing: non‑coding sequences known as introns are removed, and coding sequences called exons are spliced together to produce a mature mRNA molecule ready for export from the nucleus.
Prokaryotes, lacking a defined nucleus, perform transcription and translation in the cytoplasm concurrently, simplifying the pathway.
Once inside the cytoplasm, the mature mRNA binds to a ribosome—the cell’s protein factory. Ribosomes read the mRNA in sets of three nucleotides, called codons, each of which specifies a particular amino acid.
Transfer RNA (tRNA) molecules carry amino acids and possess anticodons that are complementary to the mRNA codons. As each codon is matched to its tRNA, the corresponding amino acid is added to the growing polypeptide chain.
For example, the codon AUG codes for the amino acid methionine, often serving as the start signal for translation. The process continues until a stop codon signals termination, yielding a fully formed protein.
