What is Gene Expression?

Almost every cell in the body contains the entire genome, but only some genes are actually expressed into proteins, and these differ between cells. For instance, neurons and muscle cells express different genes, allowing them to have different specialized functions.

The process of gene expression starts with transcription, when DNA acts as a template for RNA synthesis.

The RNA transcript then undergoes splicing, the removal of non-coding intron sequences, leaving the coding exons. The final result is messenger RNA, mRNA, that then travels to the ribosome in eukaryotic cells. Here, transfer RNA, tRNA molecules, translate the three nucleotide codons in the mRNA, into a sequence of amino acids.

The resulting polypeptide chain of amino acids usually then undergoes further processing to become a functional protein.

Gene expression can be regulated at any point in this process. For example, epigenetic modifications that alter the structure of the DNA molecule, without changing its sequence, can inhibit or promote transcription of certain genes.

Also, once a gene is transcribed, translation can be inhibited, for instance, by small regulatory RNAs, stopping the gene from being expressed into protein.