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Bacteria use two broad types of autoinducers during quorum sensing that act through different mechanisms. How does each type act?
ASmall hydrophobic AHL stimulates kinase pathways, peptide autoinducers bind transcription factors
BBoth AHL and peptide autoinducers bind transcription factors the same way
CPeptide autoinducers cross the membrane freely, but hydrophobic AHL cannot cross at all
DSmall hydrophobic AHL binds transcription factors, larger peptide autoinducers stimulate kinase pathways
Answer & Solution
Correct answer: D. Small hydrophobic AHL binds transcription factors, larger peptide autoinducers stimulate kinase pathways
1. Quorum sensing uses autoinducers as signaling molecules, which can be small hydrophobic molecules or larger peptide-based molecules.
2. The small hydrophobic autoinducers, such as acyl-homoserine lactone or AHL, enter target bacteria and bind transcription factors directly.
3. This binding switches gene expression on or off.
4. The peptide autoinducers instead stimulate more complicated signaling pathways that include bacterial kinases.
5. The option that swaps the two mechanisms, giving peptide autoinducers the direct transcription-factor role, reverses the actual mechanism described.
6. Describing both types as acting identically ignores the explicit contrast drawn between the two mechanisms.
7. The claim that peptide autoinducers diffuse across the membrane while hydrophobic ones cannot is not supported; AHL is described as small and hydrophobic, which typically favors membrane entry.
_Source: OpenStax Biology (1st ed., CC BY 4.0), Ch 9 "Cell Communication", section Signaling in Bacteria_
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