The Operon Theory of Gene Regulation Explains How the Production of Proteins is Regulated in Bacteria.

Reading Passage Question

The operon theory of gene regulation explains how the production of proteins is regulated in bacteria. A complex of genes, the operon consists of two regions: a coding region, for enzymes involved in a metabolic pathway, and a regulatory region that determines whether the gene is switched “on” or “off.” There are two types of operons. In an inducible operon, protein production is “off” by default, and turns “on” when a sufficient quantity of inducer is present. In a repressible operon, protein production is “on” by default, and turns “off” when an active repressor complex is present.

The lac operon is an example of an inducible operon. Normally, the lac operon's protein production is inactive; since the lac repressor is bound to the regulatory region, the gene does not produce enzymes. However, when lactose, or milk sugar, is present in high concentrations, the lac repressor binds instead to the lactose. Since the regulatory region is now free of a repressor, the gene activates and begins to produce proteins.

The process is neatly self-regulating. The proteins produced by the now-activated genes’ lactose-digesting enzymes, which in turn down the lactose. Once all lactose is broken down, there is no remaining lactose that can bind to the Lac repressor. The repressor returns to the regulatory region, turning the operon “off” and arresting the production of enzymes and the digestion of lactose.

“The operon theory of gene regulation explains how the production of proteins is regulated in bacteria.” - this is a GMAT reading comprehension passage with answers. Candidates need a strong knowledge of English GMAT reading comprehension.

This GMAT Reading Comprehension consists of 3 comprehension questions. The GMAT Reading Comprehension questions are designed for the purpose of testing candidates’ abilities in understanding, analyzing, and applying information or concepts. Candidates can actively prepare with the help of GMAT Reading Comprehension Practice Questions.

Solution and Explanation

1. Which of the following best describes the structure of the passage?

1. explains a theory by describing its execution
2. hypothesizes a reason for a phenomenon
3. describes a theory in scientific research
4. explores the possibilities induced by a theory
5. demonstrates a concept with a specific example

2. Which of the following can be inferred from the passage?

1. All genes are either inducible or repressible
2. Lactose is the inducer of the /lac operon
3. The lac repressor prefers to bind to lactose rather than the regulatory region
4. The repressible operon does not normally have anything bound to its regulatory region
5. Lactose is the main source of energy for bacteria

3. According to the passage, what is the purpose of the lac repressor?

1. it prevents lactose from binding to the regulatory region
2. it forms the active repressor complex in a repressible operon
3. when present in high concentrations, it inhibits the activation of lactose-digesting enzymes
4. when bound to enzymes, it prevents lactose digestion
5. when bound to the regulatory region, it turns the /lac operon "off," halting enzyme production

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