Slide 1 of 26 Copyright Pearson Prentice Hall 12-5 Gene Regulation Fruit fly chromosome Fruit fly embryo Adult fruit fly Mouse chromosomes Mouse embryo Adult mouse

12-5 Gene Regulation Slide 2 of 26 Copyright Pearson Prentice Hall 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.

12-5 Gene Regulation Slide 3 of 26 Copyright Pearson Prentice Hall Gene Regulation: An Example How are lac genes turned off and on?

12-5 Gene Regulation Slide 4 of 26 Copyright Pearson Prentice Hall Gene Regulation: An Example The lac genes are turned off by repressors and turned on by the presence of lactose.

12-5 Gene Regulation Slide 5 of 26 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.

12-5 Gene Regulation Slide 6 of 26 Copyright Pearson Prentice Hall Gene Regulation: An Example The other region is the operator (O).

12-5 Gene Regulation Slide 7 of 26 Copyright Pearson Prentice Hall Gene Regulation: An Example When the lac repressor binds to the O region, transcription is not possible.

12-5 Gene Regulation Slide 8 of 26 Copyright Pearson Prentice Hall Gene Regulation: An Example When lactose is added, sugar binds to the repressor proteins.

12-5 Gene Regulation Slide 9 of 26 Copyright Pearson Prentice Hall Gene Regulation: An Example The repressor protein changes shape and falls off the operator and transcription is made possible.

12-5 Gene Regulation Slide 10 of 26 Copyright Pearson Prentice Hall 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.

12-5 Gene Regulation Slide 11 of 26 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. Copyright Pearson Prentice Hall

12-5 Gene Regulation Slide 12 of 26 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 product is not consumed by some other process. Copyright Pearson Prentice Hall

12-5 Gene Regulation Slide 13 of 26 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 Copyright Pearson Prentice Hall

12-5 Gene Regulation Slide 14 of 26 positive vs. negative feedback What are examples of Positive Feedback? Clotting mechanism in blood Panic in cattle herds Copyright Pearson Prentice Hall

12-5 Gene Regulation Slide 15 of 26 Copyright Pearson Prentice Hall Eukaryotic Gene Regulation How are most eukaryotic genes controlled?

12-5 Gene Regulation Slide 16 of 26 Copyright Pearson Prentice Hall 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.

12-5 Gene Regulation Slide 17 of 26 Copyright Pearson Prentice Hall Eukaryotic Gene Regulation Many eukaryotic genes have a sequence called the TATA box. Promoter sequences Upstream enhancer TATA box Introns Exons Direction of transcription

12-5 Gene Regulation Slide 18 of 26 Copyright Pearson Prentice Hall Eukaryotic Gene Regulation The TATA box seems to help position RNA polymerase. Promoter sequences Upstream enhancer TATA box Introns Exons Direction of transcription

12-5 Gene Regulation Slide 19 of 26 Copyright Pearson Prentice Hall Eukaryotic Gene Regulation Eukaryotic promoters are usually found just before the TATA box, and consist of short DNA sequences. Promoter sequences Upstream enhancer TATA box Introns Exons Direction of transcription

12-5 Gene Regulation Slide 20 of 26 Copyright Pearson Prentice Hall 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

12-5 Gene Regulation Slide 21 of 26 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.

12-5 Gene Regulation Slide 22 of 26 Copyright Pearson Prentice Hall 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.

12-5 Gene Regulation Slide 23 of 26 Copyright Pearson Prentice Hall Development and Differentiation Hox Genes Fruit fly chromosome Fruit fly embryo Adult fruit fly Mouse chromosomes Mouse embryo Adult mouse

12-5 Gene Regulation Slide 24 of 26 Copyright Pearson Prentice Hall

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Slide 26 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

Slide 27 of 26 Copyright Pearson Prentice Hall 12–5 A group of genes that operates together is a(an) a.promoter. b.operon. c.operator. d.intron.

Slide 28 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 29 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 30 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.

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