Part I: Repression The lac operon is a classic example of gene regulation in bacteria. The operon itself is a cluster of genes that are under both negative (driven by a repressor protein) and positive (driven by an activator protein) control of expression (i.e. transcription and translation!). In this exercise you will review and practice describing negative control of the lac operon. Redraw the operon using some kind of color coding (refer to Figure 1). Answer the following questions as you work through the steps of negative regulation. Make sure that each member of the group takes a turn in explaining the operon to the fellow members. CAP cAMP RNA Polymerase P Lac I C P O Lac Z Lac Y Lac A 5' 3' Repressor 5' 3' Allolactose ?-galactosidase Lactose permease Transacetylase
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In the absence of lactose, the lac repressor protein binds to the operator region of the lac operon. This prevents RNA polymerase from binding to the promoter region and initiating transcription of the lac genes. Therefore, the lac operon is not expressed, and no Show more…
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The lac operon is a classic example of gene regulation in bacteria. The operon itself is a cluster of genes that are under both negative (driven by a repressor protein) and positive (driven by an activator protein) control of expression (i.e., transcription and translation). In this exercise, you will review and practice describing the negative control of the lac operon. Redraw the operon using some kind of color coding (refer to Figure). Answer the following questions as you work through the steps of negative regulation. Make sure that each member of the group takes turns in explaining the operon to the fellow members. cAMP Polymerase Repressor Galactosidase Lactose permease Transacetylase
Madhur L.
The diagram below shows the 'lac operon' which is a control system of gene expression regulating lactose metabolism in the bacterium E. coli. Genes z, y and a control the synthesis of the enzymes which are responsible for the metabolism of lactose in the bacterial cell. Gene i is a regulator gene controlling the expression of genes z, y and a. p is the promotor region to which RNA polymerase attaches during transcription of DNA to mRNA. o is the operator site to which the repressor protein can attach. In the presence of lactose, the bacteria can produce the enzymes to metabolize lactose. If the bacteria are subculture onto a lactose free substrate, they cease to produce the enzymes for metabolizing lactose, within three minutes. (a) Describe how the lac operon system works to repress the formation of the lactose metabolizing enzymes.
Sri K.
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