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A major group of G-protein-coupled receptors contains seven transmembrane α helices. The amino end of the protein lies at the exterior of the plasma membrane. Loops of amino acids connect the helices either at the exterior face or on the cytosol face of the membrane. The loop on the cytosol side between helices 5 and 6 is usually substantially longer than the others.
-Which of the following processes includes all the others?

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Quizplus · Accepted Answer

All the processes listed (osmosis, diffusion of a solute across a membrane, facilitated diffusion, and transport of an ion down its electrochemical gradient) are examples of passive transport, which does not require input of energy and occurs down a concentration gradient. The seven transmembrane alpha helices described in the passage are characteristic of G-protein-coupled receptors, which are integral membrane proteins that function to transmit signals from the exterior to the interior of the cell via a complex signaling pathway. However, this description is not directly related to any of the processes listed, except in the sense that they all involve movement across a biological membrane.

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