Advanced Cell Membrane Quiz || Membrane Transport Quiz | Cell Biology Quiz

Advanced Cell Membrane Quiz

1. Which of the following best describes the energetic favorability of a transmembrane protein folding with its hydrophobic residues exposed to the aqueous extracellular environment?

a) Highly favorable due to increased entropy of water. b) Highly unfavorable due to disruption of hydrogen bonding networks in water. c) Neutral, as protein folding is independent of the surrounding environment. d) Favorable, provided the protein also possesses sufficient hydrophilic residues.

Explanation: Exposing hydrophobic residues to water would force water molecules into an ordered cage-like structure, decreasing entropy, which is highly unfavorable energetically.

2. A novel antibiotic is discovered that specifically inhibits the activity of flippases. What would be the most immediate and significant consequence for a eukaryotic cell treated with this antibiotic?

a) Impaired cholesterol synthesis and membrane fluidity. b) Disrupted formation of clathrin-coated pits during endocytosis. c) Accumulation of phosphatidylserine on the outer leaflet, leading to potential apoptotic signals. d) Enhanced lateral diffusion of integral membrane proteins.

Explanation: Flippases are responsible for translocating specific phospholipids, particularly phosphatidylserine, from the exoplasmic to the cytosolic leaflet. Inhibition would lead to its accumulation on the outer leaflet, a signal for apoptosis.

3. The selective permeability of the cell membrane is primarily attributed to:

a) The presence of specific carbohydrate chains on the outer surface. b) The inherent amphipathic nature of phospholipids, creating a hydrophobic barrier. c) The differential distribution of ions across the membrane. d) The dynamic fluidity of the lipid bilayer allowing rapid solute movement.

Explanation: The hydrophobic core formed by the fatty acid tails of phospholipids is the primary barrier to the passage of most polar and charged molecules.

4. Which experimental approach would be most effective in determining the average residence time of a specific lipid molecule within a defined microdomain (e.g., a lipid raft) on the cell membrane?

a) Fluorescence Recovery After Photobleaching (FRAP) of a fluorescently tagged lipid. b) Atomic Force Microscopy (AFM) to visualize membrane topography. c) Cryo-electron tomography of the intact cell membrane. d) SDS-PAGE followed by Western blot analysis of membrane proteins.

Explanation: FRAP directly measures the lateral diffusion rates and recovery of fluorescent molecules within a bleached area, providing insights into their residence time in specific regions.

5. The movement of a glucose molecule from an area of higher concentration outside the cell to an area of lower concentration inside the cell, *requiring the assistance of a transmembrane protein but no direct ATP hydrolysis*, is an example of:

a) Primary active transport. b) Secondary active transport. c) Facilitated diffusion. d) Simple diffusion.

Explanation: Facilitated diffusion uses a carrier protein or channel to move molecules down their concentration gradient without direct energy expenditure.

6. Considering the biophysical properties of the lipid bilayer, which modification would *decrease* the overall fluidity of a eukaryotic cell membrane at a given temperature?

a) An increase in the proportion of unsaturated fatty acid chains. b) A decrease in cholesterol content. c) An increase in the average length of fatty acid chains. d) An increase in the concentration of integral membrane proteins.

Explanation: Longer fatty acid chains have more Van der Waals interactions, leading to tighter packing and reduced fluidity.

7. A mutation in a gene encoding a specific aquaporin results in a non-functional channel. What would be the most likely consequence for a cell exposed to a hypotonic solution?

a) Increased rate of cell swelling and lysis. b) Decreased water influx, potentially leading to cell shrinkage. c) Unchanged water movement due to alternative transport mechanisms. d) Enhanced activity of the Na+/K+ ATPase to compensate for osmotic imbalance.

Explanation: Aquaporins greatly facilitate water movement. Their absence would significantly slow down water influx, even in a hypotonic environment, hindering the cell's ability to take up water and potentially leading to shrinkage or at least less swelling than expected.

8. Which of the following statements most accurately describes the role of glycocalyx components in cell-cell recognition and adhesion?

a) They primarily function as structural supports, maintaining cell shape. b) They form a selectively permeable barrier, regulating ion flow. c) They serve as specific binding sites for extracellular matrix components and other cells. d) They are involved in ATP synthesis and energy production at the membrane surface.

Explanation: The glycocalyx, composed of glycoproteins and glycolipids, plays crucial roles in cell recognition, adhesion, and signaling.

9. The energy required for the movement of Na+ ions into a eukaryotic cell against their concentration gradient, often coupled to the transport of another molecule, is typically derived from:

a) Direct hydrolysis of ATP by the symporter/antiporter. b) The electrochemical gradient of K+ ions. c) The proton gradient across the mitochondrial inner membrane. d) The Na+ electrochemical gradient established by the Na+/K+ ATPase.

Explanation: Secondary active transport, which includes many Na+-coupled transporters, utilizes the pre-existing Na+ gradient (created by the Na+/K+ ATPase) as its energy source.

10. In a classic Frye and Edidin experiment, human and mouse cells were fused and their membrane proteins observed. The rapid intermixing of these proteins after fusion provided strong evidence for:

a) The fluid mosaic model of the cell membrane. b) The existence of distinct lipid rafts. c) The role of the cytoskeleton in membrane protein localization. d) The transmembrane nature of integral membrane proteins.

Explanation: The rapid intermixing demonstrated the lateral mobility of membrane components, a key tenet of the fluid mosaic model.