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12-5 Gene Regulation Fruit fly chromosome Mouse chromosomes 12-5 Gene Regulation Fruit fly embryo Mouse embryo Adult fruit fly Copyright Pearson Prentice Hall Adult mouse Slide 1 of 26 12-5 Gene Regulation Gene Regulation: An Example Gene Regulation: An Example E. coli provides an example of how gene expression can be regulated. An operon is a group of genes that operate together. In E. coli, these genes must be turned on so the bacterium can use lactose as food. Therefore, they are called the lac operon. Slide 2 of 26 Copyright Pearson Prentice Hall 12-5 Gene Regulation Gene Regulation: An Example How are lac genes turned off and on? Slide 3 of 26 Copyright Pearson Prentice Hall 12-5 Gene Regulation Gene Regulation: An Example The lac genes are turned off by repressors and turned on by the presence of lactose. Slide 4 of 26 Copyright Pearson Prentice Hall 12-5 Gene Regulation 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. Slide 5 of 26 Copyright Pearson Prentice Hall 12-5 Gene Regulation Gene Regulation: An Example • The other region is the operator (O). Slide 6 of 26 Copyright Pearson Prentice Hall 12-5 Gene Regulation Gene Regulation: An Example When the lac repressor binds to the O region, transcription is not possible. Slide 7 of 26 Copyright Pearson Prentice Hall 12-5 Gene Regulation Gene Regulation: An Example When lactose is added, sugar binds to the repressor proteins. Slide 8 of 26 Copyright Pearson Prentice Hall 12-5 Gene Regulation Gene Regulation: An Example The repressor protein changes shape and falls off the operator and transcription is made possible. Slide 9 of 26 Copyright Pearson Prentice Hall 12-5 Gene Regulation Gene Regulation: An Example Many genes are regulated by repressor proteins. Some genes use proteins that speed transcription. Sometimes regulation occurs at the level of protein synthesis. Slide 10 of 26 Copyright Pearson Prentice Hall 12-5 Gene Regulation positive vs. negative feedback Many molecular and physiological processes are controlled by feedback mechanisms. In a feedback loop the product of a process, such as the breakdown of proteins into amino acids, has an effect on the rate of the process. Slide 11 of 26 Copyright Pearson Prentice Hall 12-5 Gene Regulation positive vs. negative feedback Negative feedback occurs when the rate of the process decreases as the concentration of the product increases (or reactant decreases). Positive feedback occurs when the rate of a process increases as the concentration of the product increases (or reactant decreases). Negative feedback controls the rate of a process to avoid accumulation of a product. The rate of a process will continuously accelerate under positive feedback as long as substrate is available and the Slide product is not consumed by some other process. 12 of 26 Copyright Pearson Prentice Hall 12-5 Gene Regulation positive vs. negative feedback What kind of feedback is the lac operon? • Negative Feedback (lac operon is turned on, lactose is digested, lactose is removed, lac operon turns back off) What are other examples of Negative Feedback? • Sweating and temperature regulation • Predator-Prey interactions Slide 13 of 26 Copyright Pearson Prentice Hall 12-5 Gene Regulation positive vs. negative feedback What are examples of Positive Feedback? • Clotting mechanism in blood • Panic in cattle herds Slide 14 of 26 Copyright Pearson Prentice Hall 12-5 Gene Regulation Eukaryotic Gene Regulation How are most eukaryotic genes controlled? Slide 15 of 26 Copyright Pearson Prentice Hall 12-5 Gene Regulation Eukaryotic Gene Regulation Eukaryotic Gene Regulation Operons are generally not found in eukaryotes. Most eukaryotic genes are controlled individually and have regulatory sequences that are much more complex than those of the lac operon. Slide 16 of 26 Copyright Pearson Prentice Hall 12-5 Gene Regulation Eukaryotic Gene Regulation Many eukaryotic genes have a sequence called the TATA box. Upstream enhancer TATA box Promoter sequences Introns Exons Direction of transcription Slide 17 of 26 Copyright Pearson Prentice Hall 12-5 Gene Regulation Eukaryotic Gene Regulation The TATA box seems to help position RNA polymerase. Upstream enhancer TATA box Promoter sequences Introns Exons Direction of transcription Slide 18 of 26 Copyright Pearson Prentice Hall 12-5 Gene Regulation Eukaryotic Gene Regulation Eukaryotic promoters are usually found just before the TATA box, and consist of short DNA sequences. Upstream enhancer TATA box Promoter sequences Introns Exons Direction of transcription Slide 19 of 26 Copyright Pearson Prentice Hall 12-5 Gene Regulation Eukaryotic Gene Regulation Genes are regulated in a variety of ways by enhancer sequences. Many proteins can bind to different enhancer sequences. Some DNA-binding proteins enhance transcription by: • opening up tightly packed chromatin • helping to attract RNA polymerase • blocking access to genes Slide 20 of 26 Copyright Pearson Prentice Hall 12-5 Gene Regulation Development and Differentiation 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. Slide 21 of 26 Copyright Pearson Prentice Hall 12-5 Gene Regulation Development and Differentiation Careful control of expression in hox genes is essential for normal development. All hox genes are descended from the genes of common ancestors. Slide 22 of 26 Copyright Pearson Prentice Hall 12-5 Gene Regulation Development and Differentiation Hox Genes Fruit fly chromosome Mouse chromosomes Fruit fly embryo Mouse embryo Adult fruit fly Copyright Pearson Prentice Hall Adult mouse Slide 23 of 26 12-5 Gene Regulation Slide 24 of 26 Copyright Pearson Prentice Hall 12–5 Click to Launch: Continue to: - or - Slide 25 of 26 Copyright Pearson Prentice Hall 12–5 Which sequence shows the typical organization of a single gene site on a DNA strand? a. start codon, regulatory site, promoter, stop codon b. regulatory site, promoter, start codon, stop codon c. start codon, promoter, regulatory site, stop codon d. promoter, regulatory site, start codon, stop codon Copyright Pearson Prentice Hall Slide 26 of 26 12–5 A group of genes that operates together is a(an) a. promoter. b. operon. c. operator. d. intron. Slide 27 of 26 Copyright Pearson Prentice Hall 12–5 Repressors function to a. turn genes off. b. produce lactose. c. turn genes on. d. slow cell division. Slide 28 of 26 Copyright Pearson Prentice Hall 12–5 Which of the following is unique to the regulation of eukaryotic genes? a. promoter sequences b. TATA box c. different start codons d. regulatory proteins Slide 29 of 26 Copyright Pearson Prentice Hall 12–5 Organs and tissues that develop in various parts of embryos are controlled by a. regulation sites. b. RNA polymerase. c. hox genes. d. DNA polymerase. Slide 30 of 26 Copyright Pearson Prentice Hall END OF SECTION