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A gene is a specific segment of DNA located on a chromosome that contains the instructions for producing a particular RNA transcript and ultimately a protein. The portion of a gene that is translated into protein is called the open reading frame (ORF). Control of ORF transcription is governed by regulatory sequences—promoters, enhancers, and silencers—located within or adjacent to the gene. These regulatory elements orchestrate gene activation without encoding any protein themselves.
Not all RNA molecules serve as templates for proteins. Ribosomal RNA (rRNA) forms the structural and catalytic core of ribosomes, while transfer RNA (tRNA) delivers amino acids during translation. MicroRNAs (miRNAs) are short, ~22‑nt RNAs that bind complementary mRNA sequences, leading to their degradation or translational repression—a process known as RNA interference. Other non‑coding RNAs (e.g., long non‑coding RNAs) play roles in chromatin remodeling and transcriptional regulation.
During maturation of messenger RNA (mRNA), the pre‑mRNA transcript contains both exons (coding) and introns (non‑coding). Splicing removes introns and, in some cases, certain exons—a mechanism called alternative splicing—that generates multiple protein isoforms from a single gene. This post‑transcriptional editing expands proteomic diversity.
Large stretches of the genome have historically been labeled "junk DNA" because no clear function was known. These sequences are abundant in telomeres, the protective caps at chromosome ends. Telomeric repeats are largely non‑coding, allowing chromosomes to shorten safely during cell division without risking loss of essential genes. Recent research suggests many of these regions may have regulatory roles yet to be uncovered.
