Multiple Choice
Which of the following is commonly found as part of the resident flora of the human intestines?
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1. Introduction to Microbiology
Members of the Bacterial World
Multiple Choice
Which of the following statements is true about Escherichia coli (E. coli) bacteria in an environment lacking lactose?
A
The lac operon is induced, leading to high levels of β-galactosidase production.
B
E. coli uses lactose as its primary energy source.
C
The lac operon is repressed, and genes for lactose metabolism are not transcribed.
D
Allolactose binds to the repressor, allowing transcription of the lac operon.
Verified step by step guidance1
Understand the role of the lac operon in Escherichia coli: it controls the metabolism of lactose by regulating the production of enzymes like β-galactosidase.
Recall that the lac operon is typically repressed when lactose is absent because the repressor protein binds to the operator region, preventing transcription of the operon's genes.
Recognize that allolactose, an isomer of lactose, acts as an inducer by binding to the repressor and causing it to release from the operator, but this only happens when lactose is present.
Analyze the statements given: if lactose is absent, the lac operon should be repressed, meaning no transcription of lactose metabolism genes and no β-galactosidase production.
Conclude that the true statement is the one indicating that the lac operon is repressed and genes for lactose metabolism are not transcribed in the absence of lactose.
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