Eukaryotic Gene Regulation How are most eukaryotic genes controlled? In other words, how are the genes ‘told’ to turn on/off? Copyright Pearson Prentice Hall

Eukaryotic Gene Regulation Many eukaryotic genes have a sequence called the TATA box; it is part of the promoter. TATA box Upstream enhancer Introns Promoter sequences Exons Many eukaryotic genes include a sequence called the TATA box that may help position RNA polymerase. Eukaryotic genes have regulatory sequences that are more complex than prokaryotic genes. Direction of transcription Copyright Pearson Prentice Hall

Eukaryotic Gene Regulation The TATA box seems to help position RNA polymerase, so that transcription can occur. Upstream enhancer TATA box Introns Promoter sequences Exons Many eukaryotic genes include a sequence called the TATA box that may help position RNA polymerase. Eukaryotic genes have regulatory sequences that are more complex than prokaryotic genes. Direction of transcription Copyright Pearson Prentice Hall

Eukaryotic Gene Regulation Eukaryotic promoters are usually found just before the TATA box, and consist of short DNA sequences. Upstream enhancer TATA box Introns Promoter sequences Exons Many eukaryotic genes include a sequence called the TATA box that may help position RNA polymerase. Eukaryotic genes have regulatory sequences that are more complex than prokaryotic genes. Direction of transcription Copyright Pearson Prentice Hall

Gene products turn on/off genes Copyright Pearson Prentice Hall

Tryptophan=on/off switch Copyright Pearson Prentice Hall

Development and Differentiation As cells grow and divide, they undergo differentiation, meaning they become specialized in structure and function. Hox genes control the differentiation of cells and tissues in the embryo. They are master genes—lay out the body plan; tell other genes to do their thing Copyright Pearson Prentice Hall

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Copyright Pearson Prentice Hall

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Development and Differentiation Hox Genes are universal to animals Fruit fly chromosome Mouse chromosomes Fruit fly embryo Mouse embryo n fruit flies, a series of hox genes along a chromosome determines the basic structure of the fly’s body. Mice have very similar genes on four different chromosomes. The color bars along the mouse’s back show the approximate body area affected by genes of the corresponding colors. Adult fruit fly Adult mouse Copyright Pearson Prentice Hall

Gene Regulation: An Example How are genes turned on and off in PROKARYOTIC CELLS, like bacteria??? Copyright Pearson Prentice Hall

Gene Regulation: An Example Bacteria turn on/off genes, too. An example of this are the “lac” genes The lac genes (genes to use lactose) are turned off by repressors and turned on by the presence of lactose. You only want to make the digestive proteins when needed…. Thus, being able to turn on/off genes is an example of FEEDBACK. Think of a thermostat…. Copyright Pearson Prentice Hall

Gene Regulation: An Example On one side of the operon's three genes are two regulatory regions. In the promoter (P) region, RNA polymerase binds and then begins transcription. The lac genes in E. coli are turned off by repressors and turned on by the presence of lactose. When lactose is not present, the repressor binds to the operator region, preventing RNA polymerase from beginning transcription. Lactose causes the repressor to be released from the operator region. Copyright Pearson Prentice Hall

Gene Regulation: An Example The other region is the operator (O). The lac genes in E. coli are turned off by repressors and turned on by the presence of lactose. When lactose is not present, the repressor binds to the operator region, preventing RNA polymerase from beginning transcription. Lactose causes the repressor to be released from the operator region. Copyright Pearson Prentice Hall

Gene Regulation: An Example When the lac repressor binds to the O region, transcription is not possible. The lac genes in E. coli are turned off by repressors and turned on by the presence of lactose. When lactose is not present, the repressor binds to the operator region, preventing RNA polymerase from beginning transcription. Lactose causes the repressor to be released from the operator region. Copyright Pearson Prentice Hall

Gene Regulation: An Example When lactose is added, sugar binds to the repressor proteins. The lac genes in E. coli are turned off by repressors and turned on by the presence of lactose. When lactose is not present, the repressor binds to the operator region, preventing RNA polymerase from beginning transcription. Lactose causes the repressor to be released from the operator region. Copyright Pearson Prentice Hall

Gene Regulation: An Example The repressor protein changes shape and falls off the operator and transcription is made possible. The lac genes in E. coli are turned off by repressors and turned on by the presence of lactose. When lactose is not present, the repressor binds to the operator region, preventing RNA polymerase from beginning transcription. Lactose causes the repressor to be released from the operator region. Copyright Pearson Prentice Hall