Gene expression is the fundamental process by which information encoded in a gene is converted into a functional product, such as a protein or a non-coding RNA molecule. This process is central to all known life forms, dictating the characteristics and functions of cells and organisms. It involves two main stages: transcription and translation.

Transcription is the first step, where the DNA sequence of a gene is copied into an RNA molecule, specifically messenger RNA (mRNA), by an enzyme called RNA polymerase. This occurs in the nucleus of eukaryotic cells and the cytoplasm of prokaryotic cells. The mRNA then carries this genetic message out of the nucleus to the ribosomes.

Translation is the second step, where the mRNA sequence is decoded by ribosomes to synthesize a specific protein. Transfer RNA (tRNA) molecules bring specific amino acids to the ribosome, matching them to the codons (three-nucleotide sequences) on the mRNA. The amino acids are then linked together to form a polypeptide chain, which folds into a functional protein. Gene expression is tightly regulated at multiple levels (transcriptional, post-transcriptional, translational, and post-translational) to ensure that the correct proteins are produced at the right time and in the right amounts, crucial for development, cellular function, and adaptation to environmental changes.