| 单词 | operon |
| 例句 | Monod called one such gene module an operon.* The Gene 2016-06-02T00:00:00Z In 1957, Pardee, Monod, and Jacob discovered that the lactose operon was controlled by a single master switch—a protein eventually called the repressor. The Gene 2016-06-02T00:00:00Z Pardee, Jacob, and Monod published their monumental study on the lactose operon in 1959, six years after the Watson and Crick paper on the structure of DNA. The Gene 2016-06-02T00:00:00Z The first example of such control was discovered using E. coli in the 1950s and 1960s by French researchers and is called the lac operon. Concepts of Biology 2013-04-25T00:00:00Z If tryptophan is present in the environment, then E. coli does not need to synthesize it and the switch controlling the activation of the genes in the trp operon is switched off. Biology for AP Courses 2022-06-09T00:00:00Z The lac operon controls the production of proteins needed for E. coli to use lactose for food. Miller & Levine Biology 2018-01-01T00:00:00Z Greater per-genome rRNA operon copy number has been found to be associated with rapid maximum growth rates29, which may provide a selective advantage when resources are abundant, such as in animal hosts. A communal catalogue reveals Earth’s multiscale microbial diversity 2017-10-31T04:00:00Z Glucose must not be present, and lactose must be available for the lac operon to be transcribed. Biology for AP Courses 2022-06-09T00:00:00Z The operon also contains a promoter sequence to which the RNA polymerase binds to begin transcription; between the promoter and the three genes is a region called the operator. Concepts of Biology 2013-04-25T00:00:00Z Figure 16.3 The five genes that are needed to synthesize tryptophan in E. coli are located next to each other in the trp operon. Biology for AP Courses 2022-06-09T00:00:00Z When the bacterium is in an environment with lactose as a food source, the lac operon genes are transcribed. Miller & Levine Biology 2018-01-01T00:00:00Z In the presence of lactose, the lac operon will not be transcribed. Biology for AP Courses 2022-06-09T00:00:00Z In the absence of lactose, the lac operon will be transcribed. Biology for AP Courses 2022-06-09T00:00:00Z The lac operon is a stretch of DNA with three adjacent genes that code for proteins that participate in the absorption and metabolism of lactose, a food source for E. coli. Concepts of Biology 2013-04-25T00:00:00Z The five coding regions for the tryptophan biosynthesis enzymes are arranged sequentially on the chromosome in the operon. Biology for AP Courses 2022-06-09T00:00:00Z Because the three genes are “operated” together, they are called the lac operon. Miller & Levine Biology 2018-01-01T00:00:00Z What would happen if the operator sequence of the trp operon contained a mutation that prevented the repressor protein from binding to the operator? Biology for AP Courses 2022-06-09T00:00:00Z Which of the following statements describes prokaryotic transcription of the lac operon? Biology for AP Courses 2022-06-09T00:00:00Z When lactose is present but glucose is absent, the lac operon is repressed. Biology for AP Courses 2022-06-09T00:00:00Z When tryptophan is not present in the cell, the repressor by itself does not bind to the operator; therefore, the operon is active and tryptophan is synthesized. Biology for AP Courses 2022-06-09T00:00:00Z An operon is a group of genes that are regulated together. Miller & Levine Biology 2018-01-01T00:00:00Z Lactose acts as an inducer of the lac operon when glucose is absent. Biology for AP Courses 2022-06-09T00:00:00Z Lactose acts as an inducer of the lac operon when glucose is present. Biology for AP Courses 2022-06-09T00:00:00Z What would be the outcome of a mutation in one of the structural genes of the lac operon? Biology for AP Courses 2022-06-09T00:00:00Z CAP binds to the operator sequence upstream of the promoter that initiates transcription of the lac operon. Biology for AP Courses 2022-06-09T00:00:00Z To use lactose for food, the bacterium must have the proteins coded for by the genes of the lac operon. Miller & Levine Biology 2018-01-01T00:00:00Z The lac operon encodes the genes necessary to acquire and process the lactose from the local environment. Biology for AP Courses 2022-06-09T00:00:00Z However, for the lac operon to be activated, two conditions must be met. Biology for AP Courses 2022-06-09T00:00:00Z Figure 16.5 Transcription of the lac operon is carefully regulated so that its expression only occurs when glucose is limited and lactose is present to serve as an alternative fuel source. Biology for AP Courses 2022-06-09T00:00:00Z In E. coli, the trp operon is on by default, while the lac operon is off. Biology for AP Courses 2022-06-09T00:00:00Z The bacterium seems to “know” when the products of the lac operon genes are needed and when they’re not needed. Miller & Levine Biology 2018-01-01T00:00:00Z When lactose and glucose are present in the medium, transcription of the lac operon is induced. Biology for AP Courses 2022-06-09T00:00:00Z The lac operon consists of regulatory regions such as the promoter as well as the structural genes lacZ, lacY, and lacA, which code for proteins involved in lactose metabolism. Biology for AP Courses 2022-06-09T00:00:00Z The lac operon is an example of inducible control because the presence of lactose “turns on” transcription of the genes for its own metabolism. Biology for AP Courses 2022-06-09T00:00:00Z The E. coli bacteria can have several mutations that affect the lac operon system. Biology for AP Courses 2022-06-09T00:00:00Z On one side of the operon’s three genes, there are two regulatory regions. Miller & Levine Biology 2018-01-01T00:00:00Z The trp operon is an example of repressible control because it uses proteins bound to the operator sequence to physically prevent the binding of RNA polymerase. Biology for AP Courses 2022-06-09T00:00:00Z There are three ways to control the transcription of an operon: repressive control, activator control, and inducible control. Biology for AP Courses 2022-06-09T00:00:00Z Repressive control, typified by the trp operon, uses proteins bound to the operator sequence to physically prevent the binding of RNA polymerase and the activation of transcription. Biology for AP Courses 2022-06-09T00:00:00Z One mutation inhibits the ability of RNA polymerase to bind to the lac operon. Biology for AP Courses 2022-06-09T00:00:00Z The binding of the repressor protein switches the operon “off” by preventing the transcription of its genes. Miller & Levine Biology 2018-01-01T00:00:00Z In the last example—the lac operon—two conditions must be met to initiate transcription. Biology for AP Courses 2022-06-09T00:00:00Z RNA polymerase can bind to the promoter and transcribe the genes of the operon. Miller & Levine Biology 2018-01-01T00:00:00Z As a result, in the presence of lactose, the operon is automatically switched on. Miller & Levine Biology 2018-01-01T00:00:00Z |
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