12-5 Gene Regulation Pages 309 – 312 Block 1 Baker

Introduction: Only a fraction of the genes in a cell are expressed at any given time. Expressed meaning there is only a small portion that is transcribed into RNA. In DNA we have promoters, start signals, stop signals, and regulatory sites. Operon – a group of genes that operate together.

lac operon in E. coli (prokaryote) This is the group of genes that helps E. coli to utilize lactose as a food source. When lactose is NOT present a repressor attaches to the operator and the lac genes cannot be accessed. When lactose IS present the repressor moves away and the genes can be accessed.

How does prokaryotic & eukaryotic gene regulation differ? Eukaryotes do not use operons. Eukaryotic genes are controlled individually and have regulatory sequences that are much more complex than those of the lac operon.

Eukaryotic Gene Regulation Much more complicated than prokaryote gene regulation. TATA box – lets the RNA polymerase know where to start. Genes are regulated in a variety of ways by enhancer sequences that are found before the promoter sequences and TATA box.

Ways proteins can bind to enhancer sequences. Open up tightly packed chromatin. Attract Block access

Eukaryotic Gene Regulation (cont.) The complexity can be explained partly when you think about our specialized cells. The genes that code for liver enzymes, for example, are not expressed in nerve cells. Remember though ALL cells carry a complete set of our DNA even though each cell does not need every gene.

Development and Differentiation As an organism develops its cells do not just divide over and over again. The cells need to undergo differentiation so they become specialized in structure and function. Hox genes are a series of genes that control the differentiation of cells and tissues in an organism.

Hox genes – fruit flies & mice Genes are similar both in structure & function. Fruit flies – the genes are located on one chromsome. Mice – genes are spread out over 4 chromosomes. Expression – fruit flies show externally & internally in mice.

Common patterns of genetic control: This provides scientists evidence that all living things shared a common ancestor.