The Plasma Membrane

Practice: The epithelial cells that line the small intestine have microvilli, which helps them to absorb macro- and micronutrients from food within the lumen of the small intestine. Microvilli accomplish this by:

Practice: Muscarinic acetylcholine receptors (mAchRs) are proteins inserted in the membranes of various body cells. On the outside of the cell these proteins bind acetylcholine. On the inside of the cell they bind to and activate a type of protein called a GTPase. For an mAchR to bind to molecules that are both outside and inside of the cell, which of the following must it be?