Ease Into Prep with an MCAT^® Question of the Day

Prokaryotic cells have evolved a system for energy conservation by transcribing a cluster of genes as a single mRNA. The way these multiple genes can be simultaneously expressed when needed is through the existence of operons--regulatory complexes that control and coordinate protein synthesis based on cell requirements. (C) is correct.

Expert Approach:
Genetic structures are cited in the answer choices, and the stem tells me that I'm looking for the one that allows prokaryotic cells to express multiple genes simultaneously. I already know the answer: prokaryotes utilize operons for this purpose. Operons are clusters of genes under the control of a single promoter, allowing them to be transcribed together as a single mRNA molecule. This mechanism enables coordinated expression of related genes. The correct answer is (C).In fact, it turns out that operons are the only one of the four named structures that are even commonly found in prokaryotes at all - the other three being critical parts of eukaryotic genetic machinery. Moreover, two of the choices, introns (A) and exons (B), do not involve multiple genes, but are instead portions of the RNA sequence within a single gene, while histones (D) are proteins involved in eukaryotic DNA packaging.

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