Gene Regulation

Prokaryote Gene Regulation Gene regulation  the ability of an organism to control which genes are transcribed is response to the environment Controlled by an “operon”

What is an operon? Section of DNA that contains the genes for the proteins needed for a specific metabolic pathway Made of operator, promoter, regulatory gene, and the genes coding for proteins

Operator  On/off switch for transcription Promoter  binding site of RNA polymerase

Trp operon Tryptophan synthesis  5 steps – each catalyzed by a specific enzyme 5 genes coding for these enzymes are clustered together on the chromosome with a group of DNA that controls whether or not they are transcribed

Trp operon Repressible operon because transcription is normally turned off Turned on only when tryptophan levels are low and synthesis is necessary

Lac operon – Inducible operon 3 enzymes that control lactose digestion Inducer  allolactose – present in food that contains lactose Binds to repressor gene and inactivates it so transcription can begin

Eukaryote Gene Regulation Requires more than a single promoter and operator for gene regulation Transcription factors  ensure that a gene is used at the right time and that proteins are made in the right amounts

2 types of transcription factors Forms complexes that guide and stabilize the binding of the RNA polymerase to a promoter Controls the rate of transcription

Hox Genes Determine the body plan of an organism Controls differentiation (cells become specialized in structure and function) Code for transcription factors and are in the same order on the chromosome as they are in the embryo

RNA interference Small pieces of double stranded RNA in the cytoplasm are cut by an enzyme called a dicer Binds to a protein complex – one strand is degraded Binds to sequence specific sections on mRNA in the cytoplasm preventing translation