Membrane Structure and Transport - Anatomy and Physiology
- What is the glycocalyx?
- The carbohydrate coat of glycoproteins and glycolipids on the outer cell surface, used in cell recognition and adhesion.
- A red blood cell is placed in distilled water. What happens to the cell?
- It swells and may burst (hemolysis), because water moves into the cell from the hypotonic solution.
- How does primary active transport differ from secondary active transport?
- Primary active transport uses ATP directly; secondary active transport uses the energy of an ion gradient built by a primary pump.
- What concentration of NaCl solution is isotonic to human cells?
- 0.9% NaCl (normal saline). Cells placed in it neither gain nor lose water.
- A red blood cell is placed in a hypertonic solution. What happens to the cell?
- It shrinks (crenates), because water moves out of the cell toward the higher solute concentration outside.
- How does facilitated diffusion differ from simple diffusion?
- It requires a carrier or channel protein and can become saturated, but it still moves solute down its gradient without ATP.
- What is osmosis?
- The diffusion of water across a selectively permeable membrane toward the side with higher solute concentration.
- What kinds of molecules cross the lipid bilayer by simple diffusion?
- Small nonpolar (lipid-soluble) molecules such as O2, CO2 and steroids.
- What is receptor-mediated endocytosis?
- Uptake of specific molecules that bind membrane receptors, cluster in clathrin-coated pits and are brought in as vesicles, as with LDL.
- Which model describes the structure of the plasma membrane?
- The fluid mosaic model: a phospholipid bilayer in which proteins float and move laterally.
- SGLT1 carries glucose into an intestinal cell against its gradient, coupled to Na+ moving down its gradient. What transport type is this?
- Secondary active transport (symport). The Na+ gradient made by the Na+/K+ pump powers glucose uptake.
- What role does cholesterol play in the plasma membrane?
- It stabilizes the bilayer, buffers changes in fluidity with temperature and lowers permeability to small water-soluble molecules.