A B C. 2. Some genes are not regulated by gene switches. These genes are expressed constantly. What kinds of genes would be expressed constantly?

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1 STO-143 Gene Switches Intrductin Bacteria need t be very efficient and nly prduce specific prteins when they are needed. Making prteins that are nt needed fr everyday cell metablism wastes energy and raw materials. Bacteria prevent resurces (energy and raw materials) frm being wasted by switching genes ff when the prteins they prduce are nt needed. Genes fr prteins that are nly needed under certain cnditins are regulated by n ff switches. Genes are switched ON when the prteins that they prduce are needed Genes are switched OFF when the prteins that they prduce are nt needed. The diagrams belw shw three different types f bacteria (A, B, and C): A B C All genes are turned n All genes are turned ff t Sme genes are turned n t make all prteins prevent prtein prductin and thers are turned ff 1. Which f the three types f bacteria cells in the diagram abve (A, B, r C) is mst likely t survive and reprduce efficiently? Prvide an explanatin fr yur answer. 2. Sme genes are nt regulated by gene switches. These genes are expressed cnstantly. What kinds f genes wuld be expressed cnstantly? 3. Other genes are regulated by gene switches that turn them n r ff. What kinds f genes wuld be regulated by gene switches? 1

2 Part 1: Mdeling a Gene Switch in Bacteria Use the infrmatin in the Operns: Gene Switches in Bacteria sheet and materials in yur kit t make a mdel f a bacterial chrmsme with an pern that regulates the prductin f enzymes. 1. Apply labels t the straw pieces t represent DNA segments in an pern. The labels shuld be applied s they wrap arund the straws as shwn in the diagram belw. Black straw piece - Prmter label Red straw piece - Operatr label 4 Clear straw pieces Label Lactase Gene label Permease Gene label Transacetylase Gene label Regulatr Gene label 2. Use infrmatin in the Operns: Gene Switches in Bacteria sheet t make a mdel f an pern. Thread the chenille stem thrugh the labeled straw pieces t arrange them in the prper rder t represent the DNA segments in an pern. 3. What genes are included in an pern? 4. What is the functin f an pern? 2

3 5. Briefly describe the rle f the fllwing structures in gene regulatin: Regulatr Gene Operatr Prmter Structural Genes 3

4 Part 2: Mdeling the Functin f the Lac Opern One example f an pern is the lac pern that regulates genes that prduce enzymes invlved in lactse metablism. Bacteria nrmally rely n glucse in their envirnment as a fd surce. Hwever, if glucse is nt available and lactse (a disaccharide) is present in the envirnment, bacteria can survive by switching n the genes that allw them t use lactse as a fd surce. The structural genes in the lac pern cntain the DNA cde that prduces three prteins. These three prteins are enzymes invlved in lactse metablism: Lactase (als called beta galactsidase) This enzyme digests lactse t frm glucse and galactse Permease This enzyme allws lactse t enter the cell. Transacetylase The functin f this enzyme is nt knwn. When lactse is absent: A repressr prtein attaches t the peratr t blck the transcriptin f the lac pern s structural genes. This switches genes in the lac pern OFF. The structural genes that prduce the three enzymes (lactase, permease, and transacetylase) which enable bacteria t use lactse as a fd surce are nt prduced. When lactse is present: The lactse mlecule acts as inducer that changes the shape f the repressr prtein s that it cannt bind t the peratr. This switches genes in the lac pern ON. The three enzymes (lactase, permease, and transacetylase) are prduced, which enable bacteria t use lactse as a fd surce. 1. In the lac pern, a repressr prtein has the prper shape that allws it t attach t the peratr. Place the repressr prtein (hair clip) ver the peratr gene t represent an active repressr prtein that blcks the mvement f the RNA plymerase. 2. Apply the RNA plymerase label t the yellw plastic car. Hint: T make the label fit the car, yu will need t cut ut just the yellw part f the label and apply it t the tp f the car, r yu can wrap the entire label arund the tp f the car. 3. Place the RNA plymerase (yellw plastic car) n the prmter t represent the actin f RNA plymerase. 4. Nte that the repressr prtein blcks the mvement f the RNA plymerase (yellw car) alng the DNA strand. The pern is turned ff and the structural genes cannt be expressed. 4

5 5. In the space belw, draw yur mdel t shw what happens when the lac pern is turned OFF. Include and label a regulatr gene, a prmter, an peratr, three structural genes (lactase gene, permease gene, transacetylase gene), an RNA plymerase, and a repressr prtein in yur diagram. 6. Explain hw the lac pern is turned OFF when lactse is nt present. 7. When lactse is present, it acts as an inducer by attaching t the repressr prtein. This changes the shape f the repressr prtein s that it cannt bind t the peratr. Attach a Lactse label t yur hand. Lactse changes the shape f the repressr prtein s that it cannt attach t the peratr. Use yur fingers t pen the hair clip and remve it frm the peratr. 8. Place the RNA plymerase (yellw car) n the peratr. 9. With the repressr prtein remved, the RNA plymerase can mve alng the structural genes and transcribe them t make a messenger RNA mlecule. Mve the RNA plymerase (yellw car) alng the structural genes t transcribe them. 5

6 10. Transcriptin creates a lng messenger RNA mlecule. Place a yellw twist tie belw the structural genes t represent the messenger RNA prduced by transcriptin f the structural genes. 11. Ribsmes then use the cded infrmatin in the messenger RNA t create prteins. Attach three ribsmes (black beads) t the messenger RNA (twist tie). 12. Place three plastic bjects belw the messenger RNA t represent the enzymes prduced when the ribsmes translate the messenger RNA. Swrd = Lactase digests lactse t frm glucse and galactse Ring = Permease allws lactse t enter the cell Cube = Transacetylase functin nt knwn 13. In the space belw, draw yur mdel t shw what happens when the lac pern is turned ON. Include and label a regulatr gene, a prmter, an peratr, three structural genes (lactase gene, permease gene, transacetylase gene), an RNA plymerase, and a repressr prtein in yur diagram. Als include and label a lactse mlecule, an RNA mlecule, ribsmes, a lactase enzyme, a permease enzyme, and a transacetylase enzyme. 6

7 14. Explain hw the lac pern is turned ON when lactse mlecules are present. 15. One weakness f this mdel is the fact that it des nt represent the actin f the lactase mlecule. If the mdel was mre accurate, the lactase (swrd) wuld the lactse (yur hand). 16. What is the advantage t having ne prmter and ne peratr assciated with three structural genes that prduce lactse metablizing enzymes? 17. What wuld happen if the psitins f the prmter and peratr were reversed? 18. Hw might the fllwing mutatins in the lac pern affect bacterial metablism? Be specific and explain yur answer. A mutatin in the prmter A mutatin in the peratr A mutatin in ne f the structural genes A mutatin in the regulatr gene that prduces the repressr prtein 7