Why are the genes involved in lactose metabolism considered to be an operon?
a. They occupy adjacent locations on the E. coli chromosome.
b. They have a similar function.
c. They are all required for normal cell function.
d. They are all controlled by the same promoter.

Verified step by step guidance

Understand the concept of an operon: An operon is a cluster of genes that are transcribed together and controlled by a single promoter. This allows for coordinated regulation of genes that are involved in a common pathway or function.

Identify the genes involved in lactose metabolism: In E. coli, the genes involved in lactose metabolism include lacZ, lacY, and lacA. These genes encode enzymes necessary for the uptake and breakdown of lactose.

Examine the control mechanism: In the lac operon, these genes are transcribed as a single mRNA molecule from a common promoter, the lac promoter. This means they are regulated together, allowing the cell to efficiently respond to the presence or absence of lactose.

Consider the options given: Option (d) states that the genes are all controlled by the same promoter, which aligns with the definition of an operon where multiple genes are regulated together by a single promoter.

Conclude based on the definition and options: The defining feature of an operon is the shared promoter controlling multiple genes, making option (d) the correct reason why the genes involved in lactose metabolism are considered an operon.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Operon

An operon is a cluster of genes under the control of a single promoter, allowing them to be transcribed together into a single mRNA strand. This arrangement is common in prokaryotes, such as E. coli, and enables coordinated regulation of genes that are functionally related, such as those involved in lactose metabolism.

Promoter

A promoter is a DNA sequence that initiates transcription of a particular gene or group of genes. In the context of an operon, a single promoter controls the transcription of multiple genes, ensuring they are expressed simultaneously. This is crucial for the efficient regulation of metabolic pathways, like lactose metabolism in bacteria.

Lactose Metabolism in E. coli

Lactose metabolism in E. coli involves the breakdown of lactose into glucose and galactose, which the bacterium can use for energy. The genes responsible for this process are organized into the lac operon, which includes genes for lactose transport and breakdown, all regulated by a single promoter to ensure efficient response to the presence of lactose.