Chapter 40 Flashcards
- Which of the following is the primary component of biological membranes?
A) Proteins
B) Cholesterol
C) Phospholipids
D) Carbohydrates
C) Phospholipids
Rationale: Phospholipids are the major component of biological membranes, forming the lipid bilayer that provides structure and permeability properties.
- What type of movement do phospholipids primarily exhibit within the membrane?
A) Flip-flop movement
B) Lateral diffusion
C) Rotation around the axis
D) Translocation across the membrane
B) Lateral diffusion
Rationale: Phospholipids predominantly exhibit lateral diffusion, moving within the same leaflet of the bilayer. Flip-flop between leaflets is rare and requires energy.
- Which of the following best describes the fluid mosaic model of membrane structure?
A) A rigid structure with tightly packed proteins
B) A flexible lipid bilayer with proteins embedded or associated
C) A membrane with only lipid molecules
D) A fixed structure with no lateral movement
B) A flexible lipid bilayer with proteins embedded or associated
Rationale: The fluid mosaic model describes the membrane as a dynamic structure where lipids and proteins move laterally, allowing for flexibility and varied functions.
- Integral membrane proteins are characterized by which of the following?
A) They are located on the membrane surface.
B) They are associated with the lipid bilayer through ionic bonds.
C) They span the lipid bilayer.
D) They are attached to membrane lipids via covalent bonds.
C) They span the lipid bilayer.
Rationale: Integral membrane proteins typically span the entire lipid bilayer and interact with both the interior and exterior environments of the cell.
Cholesterol in biological membranes serves what primary function?
A) Increases membrane fluidity at low temperatures
B) Prevents lateral diffusion of lipids
C) Stabilizes membrane fluidity across temperature changes
D) Attaches carbohydrates to membrane proteins
C) Stabilizes membrane fluidity across temperature changes
Rationale: Cholesterol helps maintain consistent membrane fluidity by preventing the membrane from becoming too rigid in cold temperatures and too fluid in warm temperatures.
Which of the following is NOT a function of membrane proteins?
A) Enzyme activity
B) Structural support
C) Passive transport
D) DNA replication
D) DNA replication
Rationale: Membrane proteins play various roles, such as transport, signaling, and structural support, but DNA replication occurs in the nucleus, not the membrane.
Which factor is NOT a determinant of membrane fluidity?
A) Fatty acid saturation
B) Cholesterol content
C) Protein content
D) Temperature
C) Protein content
Rationale: Membrane fluidity is primarily influenced by fatty acid composition, cholesterol, and temperature, while protein content is less directly involved in fluidity regulation
Glycoproteins and glycolipids are primarily involved in which membrane function?
A) Signal transduction
B) Cell-cell recognition
C) Passive diffusion
D) Active transport
B) Cell-cell recognition.
Glycoproteins and glycolipids are involved in cell-cell recognition because their carbohydrate groups are exposed on the cell surface, playing a critical role in identifying and interacting with other cells. These interactions are essential for processes like immune response, tissue formation, and cell communication.
The asymmetric distribution of phospholipids in a membrane is mainly due to:
A) Active translocation by flippases
B) Passive diffusion across the membrane
C) Random movement of lipid molecules
D) Spontaneous lipid flip-flop
Answer: A) Active translocation by flippases
Rationale: The asymmetry of membrane phospholipids is maintained by enzymes such as flippases that actively move specific lipids between the inner and outer leaflets.
In terms of permeability, which type of molecules easily diffuse through the lipid bilayer?
A) Ions
B) Large polar molecules
C) Hydrophobic molecules
D) Proteins
C) Hydrophobic molecules
Rationale: Hydrophobic molecules, such as gases and lipid-soluble molecules, easily diffuse through the lipid bilayer, whereas ions and polar molecules require specific transport mechanisms.
A researcher is studying the dynamics of membrane fluidity in a cell with a defect in cholesterol synthesis. They observe that the membrane is significantly more fluid at physiological temperatures. Which of the following changes in the membrane’s functional properties would most likely occur due to this defect?
A) Increased ability of proteins to laterally diffuse, enhancing cell signaling
B) Disruption in membrane protein folding due to excessive fluidity
C) Reduced membrane permeability to small ions due to excessive packing
D) Increased activity of flippases, causing an imbalance in lipid distribution
B) Disruption in membrane protein folding due to excessive fluidity
Rationale: Cholesterol stabilizes membrane fluidity by preventing excessive movement of phospholipids, especially at physiological temperatures. A lack of cholesterol could result in membranes that are too fluid, disrupting membrane protein function and folding, which requires a more stable environment.
An experimental drug selectively disrupts the association of specific membrane proteins with lipid rafts. Which of the following cellular processes would be most directly affected?
A) Passive diffusion of water across the plasma membrane
B) Endocytosis mediated by clathrin-coated vesicles
C) Receptor-mediated signal transduction pathways
D) The transport of ions through ATP-dependent pumps
C) Receptor-mediated signal transduction pathways
Rationale: Lipid rafts are enriched microdomains that organize certain membrane proteins involved in signal transduction, including receptors and associated kinases. Disrupting these rafts would primarily impair receptor-mediated signaling rather than passive diffusion or ATP-dependent transport.
During apoptosis, specific lipids such as phosphatidylserine become externalized on the plasma membrane. Which of the following mechanisms best explains this redistribution of phospholipids during cell death?
A) Increased activity of floppases that transport phosphatidylserine to the outer leaflet
B) Activation of scramblases that randomly distribute phospholipids between the two leaflets
C) Inactivation of flippases that maintain phosphatidylserine on the inner leaflet
D) Enhanced diffusion of phosphatidylserine across the lipid bilayer
B) Activation of scramblases that randomly distribute phospholipids between the two leaflets
Rationale: During apoptosis, scramblases become activated and disrupt the asymmetric distribution of lipids, causing phosphatidylserine to appear on the outer leaflet of the membrane. This acts as a signal for phagocytosis by immune cells.
A patient with a rare condition has dysfunctional GPI (glycosylphosphatidylinositol)-anchored proteins. Which of the following would most likely be observed in their cells?
A) Defective energy production in mitochondria due to abnormal membrane potential
B) Impaired signal transduction processes on the outer surface of the plasma membrane
C) Disrupted intracellular trafficking of vesicles and organelles
D) Loss of asymmetric distribution of phospholipids in the plasma membrane
B) Impaired signal transduction processes on the outer surface of the plasma membrane
Rationale: GPI-anchored proteins are important for various cellular processes, including signal transduction, particularly on the extracellular surface of the plasma membrane. Dysfunction in these proteins would directly affect signaling rather than intracellular trafficking or energy production.
In a patient with a metabolic disorder affecting cholesterol synthesis, membrane fluidity is significantly altered. Which of the following compensatory changes would the cell most likely initiate to maintain membrane integrity?
A) Increase in saturated fatty acids to decrease fluidity
B) Increase in unsaturated fatty acids to increase fluidity
C) Increased production of glycolipids to replace cholesterol
D) Decreased synthesis of integral membrane proteins
A) Increase in saturated fatty acids to decrease fluidity
Rationale: In the absence of cholesterol, which normally stabilizes membrane fluidity, cells may compensate by increasing saturated fatty acids, which pack tightly and reduce fluidity. This helps maintain membrane integrity, preventing excessive fluidity that could disrupt cell function.
What kinds of forces or bonds anchor an integral membrane protein in a biological membrane?
Hydrophobic interaction between protein (htdrophobic domain )and Fatty acids (of bilayer)
