13.4 Gene regulation 5/16/19 TB page 320-325

Prokaryotic Gene Regulation Bacteria regulate genes by controlling transcription (DNA -> mRNA). Genes can be turned on and off. Operons are groups of genes with related jobs that are regulated (turned on or off) together. Examples: Carcinogens Analogy - light switches Allergies E. coli – the lac operon (TB pg 321)

The Lac Operon Found in the bacteria E. coli Regulates the genes that transcribe (DNA -> mRNA) for proteins that break down lactose. Lactose is made up of glucose and galactose and the proteins break these two down to be digested. If lactose is present or absent in the environment E. coli is able to regulate (turn on or off) the operon to break down the lactose or not (making the protein or not)

The Lac Operon Promoters Operators Control regions where RNA polymerase binds to begin transcription on DNA. When lactose is present it binds to the repressor protein so that it can no longer bind to the operator region. Then RNA polymerase is able to bind to the promoter region and can continue to perform transcription (the genes are turned on). Control regions where repressor proteins bind to DNA. The repressor proteins block RNA polymerase from transcribing the lac operon, essentially turning those genes off.

Prokaryotic Gene Regulation How are prokaryotic genes regulated? DNA-binding proteins in prokaryotes regulate genes by controlling transcription.

Eukaryotic Gene Regulation TATA box – a piece of DNA at the beginning of genes that is about 25-30 base pairs long and it binds to a protein that helps RNA polymerase begin to transcribe. (TATATA or TATAAA) Regulating genes: Controlling transcription (transcription factors) – proteins bind to regulatory DNA sequences such as the TATA box. Binding usually occurs before RNA polymerase binds to the promoter region. Cell specialization – every eukaryotic cell has all the genes of the body, but not all cells use every gene. (ex. Nerve cells won’t bother to make enzymes used only in the liver) RNA interference - microRNA (miRNA) regulate gene expression by interfering with mRNA, by attaching to a group of proteins to form a silencing complex, which then binds to and destroys the complimentary mRNA. (RNAi Technology used in research)

Genetic Control of Development Gene regulation helps cells differentiate from the original fertilized egg by turning genes off and on as the embryo develops. Homeotic genes are a set of master control genes that regulates organs in specific parts of the body. All homeotic genes share a similar DNA sequence called the homeobox sequence which codes for transcription factors that turn on other genes. (Important in cell differentiation) Ex. Hox genes

Environmental influences Environment plays a role in cell differentiation. Environmental changes are translated into hormonal changes, which can regulate gene expression. Ex: Temperature and turtle eggs Lac operon in E. coli and presence or absence of lactose Tadpoles metamorphosis sped up or slowed down Population size

What controls the development of cells and tissues in multicellular organisms?