Gene Regulation A gene (DNA) is expressed when it is made into a functional product (protein/enzyme)

Gene Regulation Only a small part of the genes in a cell are expressed at any given time To be “expressed” a gene must be transcribed and translated What controls when and/or if a gene is expressed? Recall promoters—start transcription signals—that bind to RNA polymerase

Example in prokaryotes E. coli bacterium 4288 genes in the organism A cluster of 3 can be turned “off” or “on” together Genes that operate together: operon The genes in this example are expressed to break down the sugar lactose and are therefore known as the lac operon

Example The lac genes are turned off by repressors and turned on by the presence of lactose Operator: section of DNA that binds to repressor and prevents transcription Repressor protein also has a site that binds to lactose…which then removes it from the operator When lactose is broken down the repressor protein binds to operator again

Eukaryotic gene regulation No operons in eukaryotes Most eukaryotic genes are controlled individually and have regulatory sequences that are much more complex than those of the lac operon in prokaryotes

Eukaryotic gene regulation Enhancers: regions of DNA that makes transcription more likely to happen Promoter sequences: regions of DNA that bind with RNA polymerase to start transcription TATA box: region of DNA just before genes that ensure transcription will take place Transcription factors: proteins that help to position RNA polymerase during transcription

Development and Differentiation Differentiation: cells must specialize in a multicellular organism A series of genes—hox genes—control differentiation of cells in an embryo Sometimes called “master control” genes A mutation in one of these genes will change body plan of an organism A very striking similarity exists in these genes in all animals