E. coli colonies grown on a lactose-containing medium up-regulate the production of the enzymes β-galactosidase and galactoside permease. Which of the following best explains the synchronous production of both enzymes in response to lactose?

Question

E. coli colonies grown on a lactose-containing medium up-regulate the production of the enzymes β-galactosidase and galactoside permease.  Which of the following best explains the synchronous production of both enzymes in response to lactose?

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11ec160b_3873_62fb_9249_a9d703abec83_MD0001_00 The lac operon is the sequence of the E. coli genome which is required for the metabolism of lactose. The lac operon consists of a regulatory gene (i), promoter region (p), operator region (o), and three structural genes (z, y, and a). The z gene codes for β-galactosidase (β-gal), which is primarily responsible for the hydrolysis of lactose to glucose and galactose. The y gene codes for permease, a transmembrane enzyme that increases the permeability of the cell to lactose. The a gene encodes a β-galactoside transacetylase, which transfers acetyl groups to β-galactosides and is unnecessary for lactose metabolism by E. coli. In prokaryotes, one mRNA transcript contains the sequences for many proteins, and a single mRNA molecule can be translated into multiple proteins or polypeptides. For instance, all three proteins of the lac operon (β-galactosidase, permease, and transacetylase) are synthesized from a single mRNA molecule containing the z, y, and a gene sequences, respectively. Transcription and translation of the genes of the lac operon is typically synchronous. Remember that a single mRNA molecule which codes for more than one protein is referred to as a polycistronic mRNA, and while most prokaryotic mRNA molecules are polycistronic, eukaryotic mRNA is rarely polycistronic. (Choices A - D) The lac operon, which codes for all three aforementioned proteins, is regulated by a single operator, a promoter, and a single group of regulatory elements: an inducer, repressor, and catabolite activator protein. Modulation of the transcription of this operon through binding of the operator and action of the repressor or other regulatory elements will change the transcription of all three lac-operon structural genes (z, y, and a). On the other hand, there are no operators, repressors, or inducers that can desynchronize the transcription of lac-operon structural genes. Educational Objective: Bacterial mRNA can be polycistronic, meaning that one mRNA codes for several proteins. An example of polycistronic mRNA is the bacterial lac operon, which codes for the proteins necessary for lactose metabolism by E. coli; the transcription and translation of these bacterial proteins is regulated by a single promoter, operator, and set of regulatory elements.

E Coli Colonies Grown on a Lactose-Containing Medium Up-Regulate the Production