Concept explainers
Bacterial genomes frequently contain groups of genes organized into operons. What is the biological advantage of operons to bacteria? Identify the regulatory components you would expect to find in an operon. How are the expressed genes of an operon usually arranged?
To review:
The genome of bacteria contains operons that consist of a group of genes. Describe the advantage of these operons to bacteria. Explain the expected regulatory components present in an operon. Also illustrate the arrangement of expressed genes of an operon?
Introduction:
The first operon was discovered in E. coli - “lac operon”- by a group of scientists- Francois Jacob, Andre Michel Lwoff and Jacques Monod in
Explanation of Solution
The gene expression in prokaryotes is completely dependent on the availability of the nutrients in a cell. To save energy and upsurge efficiency, bacteria have operons. The stretch of DNA that regulates the activity of structural genes and a group of genes is referred to as operons. They are regulated by positive and negative gene regulation. A single operon will give expressions of many gene products that save the energy of bacteria and increase the efficiency by gaining large amount of functional proteins. As bacteria have coupled transcription and translation, as soon as the group of genes on an operon is transcribed, they are converted to proteins. The genes are located one after another which allows protein synthesis to be controlled under a single promoter. To control the expression, the operon is switched on or off, according to the need of a cell.
The operon has regulatory components- Promoter, repressor, and activators/inducer.
The expressed genes are arranged after the regulatory region of the gene in a fashion one after another.
Operons in bacteria are described and the subsequent facts related to it are explained.
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Chapter 12 Solutions
Genetic Analysis: An Integrated Approach (3rd Edition)
- 1. a) If glucose is not available and lactose is absent from the environment, what is the status of transcription of the lac operon genes? Explain your answer from both an evolutionary perspective and in terms of negative and positive regulation of the operon? b)If glucose is not available, but lactose is available from the environment, what is the status of transcription of the lac operon genes? Explain your answer from both an evolutionary perspective and in terms of negative and positive regulation of the operon? b)arrow_forwardLet’s suppose you have isolated a mutant strain of E. coli in which the lac operon is constitutively expressed. In other words, the operon is turned on in the presence or absence of lactose. One possibility is that the mutation may block the transcription of the lacI gene, thereby preventing the synthesis of lac repressor. A second possibility is that the mutation could alter the sequence of the lac operon in a way that prevents the repressor protein from binding to the operator. How would you distinguish between these two possibilities?arrow_forward1. A)Explain the mechanism by which the lac operon is sensitive to glucose levels (presence and absence of glucose). B)If glucose levels in the cell are high and lactose is available from the environment, what is the status of transcription of the lac operon genes? Explain your answer from both an evolutionary perspective and in terms of negative and positive regulation of the operon?arrow_forward
- What are the effects of the following conditions on Lac operon of bacteria? Do not forget to mention about the role of repressor, activator, RNA polymerase in each case! A) Glucose is absent and lactose is present B) Glucose is present and lactose is present C) Glucose is present and lactose is absentarrow_forwardCompare the types of bacterial genes associated with inducible operons, those associated with repressible operons, and those that are constitutive. Predict the category into which each of the following would most likely fit: (a) a gene that codes for RNA polymerase, (b) a gene that codes for an enzyme required to break down maltose, and (c) a gene that codes for an enzyme used in the synthesis of adenine.arrow_forwardThe attenuation mechanism that helps block expression of the tryptophan operon requires all of the following, except A) O MRNA transcript of the trp leader sequence B) Oaribosome stalled at the stop codon of the trp leader transcript C) O formation of an attenuator loop D) O low intracellular levels of tryptophanarrow_forward
- What is an operon? Describe the functions of regulators, promoters,and operators.arrow_forwardIn the presence of tryptophan and the promoter sequence was mutated such that the RNA polymerase can no longer bind, the structural genes will:[ Select ] ["No longer be expressed", "Be constantly expressed", "Be deleted from the operon"] In the absence of tryptophan and the trpR repressor gene is mutated such that the repressor protein product can no longer bind to the operator, the structural genes will:[ Select ] ["No longer be expressed", "Be constantly expressed", "Be deleted from the operon"] In the presence of tryptophan and the trpR repressor gene is mutated such that the repressor protein product can no longer bind to the operator, the structural genes will:[ Select ] ["No longer be expressed", "Be constantly expressed", "Be constantly expressed"]arrow_forwardIf glucose levels in the cell are high and lactose is available from the environment, what is the status of transcription of the lac operon genes? Explain your answer from both an evolutionary perspective and in terms of negative and positive regulation of the operon?arrow_forward
- The streptolysin S toxin made by S. pyogenes is encoded by a 9-gene operon, sagABCDEFGHI. Thinking about what a 3-line diagram would look like for this operon, answer the following questions. Write numeric answers only. For example, if your answer is 6 promoters, write only 6. 1) How many promoters control the expression of these genes? 2) How many locations does RNA Polymerase bind to get full expression of these genes? 3) How many ribosome binding sites are needed for full protein expression? 4) How many start codons will be needed for full protein expression? 5) How many mRNA strands will be produced with full operon expression? 6) How many proteins will be produced with full protein expression? 1arrow_forwardLet’s suppose you have isolated a mutant strain of E. coli in which the lac operon is constitutively expressed. In other words, the operon is turned on in the presence or absence of lactose. One possibility is that the mutation mayblock the transcription of the lacI gene, thereby preventing the synthesis of lac repressor. A second possibility is that the mutation could alter the sequence of the lac operator in a way that prevents lac repressor from binding to the operator. How would you distinguish between these two possibilities?arrow_forwardA lac operon containing one mutation was cloned into a plasmid, which was introduced by transformation into a bacterium containing a wild-type lac operon. The three genes of the chromosomal operon were rendered noninducible in the presence of the plasmid. (a) What kind of mutation in the plasmid operon could have this effect? (b) Suppose the result of transformation was to cause the three plasmid lac genes to be expressed constitutively, at a high level. What type of plasmid gene mutation could have this result?arrow_forward
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