Gene Expression Activation of a gene to transcribe DNA into RNA. Regulation of protein synthesis so proteins are not always being created, and only when needed Gene expression is different for pro/eukaryotic cells. Prokaryotes: Operon – all genes associated with protein synthesis Structural Gene – gene coding for a protein Promoter -DNA section recognized by RNA Polymerase Operator – DNA section that is the on/off switch Operon Turned Off: Regulator gene codes for a repressor protein to be made Repressor attaches to DNA at the operator RNA polymerase attaches to DNA at the promoter, but is blocked by the repressor

Gene Expression Operon Turned On: Lactose binds to the repressor, changing its shape, releasing it from DNA RNA polymerase reads the structural genes Structural genes are then transcribed and translated to produce proteins If lactose levels drop, repressor attaches to DNA again

Gene Expression Eukaryotes: Enhancer – section of DNA which must be activated for transcription to occur RNA polymerase binds to DNA at a promoter Transcription factors bind to the enhancer and structural genes Trans. factor on enhancer is the “activator” A bend in the DNA brings the transcription factor to RNA polymerase to activate transcription.

Gene Expression After transcription, regulation of the gene continues… During transcription, a pre-mRNA strand is made, which cannot be made into a protein. The pre-mRNA contains repeating gene segments of: Introns – non-coding part of RNA; removed Exons – part of a gene that codes for protein; remain Introns are removed from the pre-mRNA strand Exons are spliced together Translation into proteins can take place