Membrane Structure and Function

1. Chapter 7 Membrane Structure and Function Questions prepared by Jung Choi Georgia Institute of Technology

2. Membrane Structure • Which of the following best describes the structure of a biologicalmembrane? • two layers of phospholipids with proteins embedded between the two layers • a mixture of covalently linked phospholipids and proteins that determines which solutes can cross the membrane and which cannot • two layers of phospholipids with proteins either crossing the layers or on the surface of the layers • a fluid structure in which phospholipids and proteins move freely between sides of the membrane • two layers of phospholipids (with opposite orientations of the phospholipids in each layer) with each layer covered on the outside with proteins

3. Osmosis • Which of the following statements about osmosis is correct? • a) If a cell is placed in an isotonic solution, more water will enter the cell than leaves the cell. • b) Osmotic movement of water into a cell would likely occur if the cell accumulates water from its environment. • c) The presence of aquaporins (proteins that form water channels in the membrane) should speed up the process of osmosis. • d) If a solution outside the cell is hypertonic compared to the cytoplasm, water will move into the cell by osmosis. • e) Osmosis is the diffusion of water from a region of lower water concentration to a region of higher water concentration.

4. Membrane Lipids and FluidityAn animal cell membrane will be more fluid at room temperature if it contains • more cholesterol. • longer chain fatty acids. • more cis-unsaturated and polyunsaturated fatty acids. • more trans-unsaturated fatty acids. • any of the above

5. Lipid Rafts, Cholesterol, and Membrane FluidityRegions of the plasma membrane called “lipid rafts” have high concentrations of cholesterol. Consequently, the proteins in lipid rafts • diffuse more freely in the membrane. • tend to stay clustered together. • are able to flip across the lipid bilayer from inside to outside and vice versa. • cannot function as receptors. • cannot undergo endocytosis.

6. Transmembrane DomainsWhich of the following amino acids would most likely be present in the transmembrane domain of an integral membrane protein? • a charged amino acid like lysine • a polar amino acid like serine • a special amino acid like glycine or proline • a hydrophobic amino acid like valine • any of the above, with no preference

7. Membrane Synthesis and SidednessAn oligosaccharide covalently linked to a lipid in the lumen of the rough ER may end up on the • cytoplasmic face of the plasma membrane. • extracellular face of the plasma membrane. • cytoplasmic face of a secretory vesicle. • any of the above

8. Membrane PermeabilityWhich of the following molecules will diffuse most quickly across a lipid bilayer membrane? • H2O • O2 • H2PO4– • glucose • Na+

9. OsmosisIf a marine algal cell is suddenly transferred from seawater to freshwater, the algal cell will initially • lose water and decrease in volume. • stay the same: neither absorb nor lose water. • absorb water and increase in volume.

10. Transport Kinetics: Passive DiffusionWhich of the curves below illustrates uptake of nitrous oxide into the cell, if nitrous oxide diffuses passively across the membrane? • A • B • C

11. Transport Kinetics: Passive DiffusionWhich of the curves below illustrates uptake of lactose into the cell via a passive transporter? • A • B • C

12. Transport Kinetics: Passive DiffusionWhich of the curves below illustrates uptake of phosphate into the cell by an active transport system? • A • B • C