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A signaling cell releases a small molecule that binds a specific protein on a target cell and delivers a signal. What is this released molecule called?
AA receptor
BA ligand
CA kinase
DA cofactor
Answer & Solution
Correct answer: B. A ligand
1. A ligand is defined as a molecule that binds another specific molecule and can deliver a signal in the process.
2. Ligands are released by signaling cells and interact with proteins called receptors on target cells.
3. A receptor is the protein that the ligand binds, not the signal itself, so it does not fit the description.
4. Kinases and phosphatases are enzymes that act later in a signaling pathway, not the initial released signal.
_Source: OpenStax Biology (1st ed., CC BY 4.0), Ch 9 "Cell Communication", section 9.1 Signaling Molecules and Cellular Receptors_
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