All flashcards
Flashcard 1: Which interactions most commonly anchor peripheral proteins to the membrane surface?
Answer: Electrostatic and hydrogen-bond interactions. Peripheral proteins bind via charge attractions and hydrogen bonds to polar head groups or integral proteins on the membrane surface.
Flashcard 2: What term describes movement of a phospholipid from one leaflet to the other?
Answer: Flip-flop (transverse diffusion). This rare movement requires crossing the hydrophobic core, which is energetically unfavorable without enzymatic assistance.
Flashcard 3: What is an integral (transmembrane) membrane protein?
Answer: Protein embedded in bilayer, often spanning it. These proteins integrate deeply into the lipid bilayer through hydrophobic domains, often traversing it to connect intracellular and extracellular environments.
Flashcard 4: Which membrane proteins are most directly responsible for selective ion passage across membranes?
Answer: Ion channels and transporters (carriers/pumps). These proteins form selective pores or undergo conformational changes to facilitate controlled ion movement across the impermeable lipid bilayer.
Flashcard 5: Identify the best description of the plasma membrane as a barrier: What property makes it selectively permeable?
Answer: Hydrophobic core excludes most polar and charged solutes. The nonpolar interior of the phospholipid bilayer acts as a barrier, permitting nonpolar solutes while restricting polar and ionic ones.
Flashcard 6: Which change to fatty acid tails increases membrane fluidity at a given temperature?
Answer: Increase unsaturated (cis) fatty acid tails. Cis double bonds create kinks that disrupt tight packing of tails, allowing greater molecular motion and thus higher fluidity.
Flashcard 7: How does increasing fatty acid tail length affect membrane fluidity and permeability?
Answer: Decreases fluidity and decreases permeability. Longer tails enhance van der Waals interactions, leading to tighter packing that reduces both fluidity and the ability of solutes to permeate.
Flashcard 8: What is a peripheral membrane protein?
Answer: Protein loosely bound to membrane surface or other proteins. These proteins associate temporarily with the membrane via non-covalent interactions without embedding into the lipid core.
Flashcard 9: What term describes the temperature at which a membrane shifts from gel-like to fluid-like?
Answer: Transition temperature (melting temperature). This temperature marks the point where thermal energy overcomes tail packing forces, transitioning the membrane from a rigid gel to a fluid state.
Flashcard 10: At low temperature, how does cholesterol affect membrane fluidity?
Answer: Increases fluidity by preventing tight packing. Cholesterol disrupts the ordered gel phase by inserting between tails, maintaining a more fluid state in cold conditions.
Flashcard 11: At high temperature, how does cholesterol affect membrane fluidity?
Answer: Decreases fluidity by restraining phospholipid movement. Cholesterol fills spaces and interacts with tails to limit excessive motion, preventing the membrane from becoming too fluid in heat.
Flashcard 12: Which solute crosses a pure phospholipid bilayer most readily: b^1) bda+, b^2) glucose, b^3) O2, b^4) H2O?
Answer: O2. As a small nonpolar gas, O2 diffuses easily through the hydrophobic bilayer core, unlike charged ions or polar molecules like glucose and water.
Flashcard 13: What is the main structural difference between saturated and unsaturated fatty acid tails in membranes?
Answer: Unsaturated tails have cis double bonds that kink. Cis double bonds in unsaturated tails introduce bends that prevent close packing, unlike the straight chains of saturated tails.
Flashcard 14: Which membrane component primarily forms the semipermeable barrier to polar solutes?
Answer: Phospholipid bilayer hydrophobic core. The nonpolar interior of the bilayer repels polar and charged molecules, allowing selective passage primarily for nonpolar substances while blocking others.
Flashcard 15: Which enzyme class catalyzes phospholipid flip-flop to help maintain membrane asymmetry?
Answer: Flippases, floppases, and scramblases. These ATP-dependent enzymes translocate phospholipids across leaflets to establish and preserve asymmetric lipid distributions.
Flashcard 16: Which is faster in membranes: lateral diffusion or flip-flop of phospholipids?
Answer: Lateral diffusion is much faster. Lateral diffusion occurs rapidly in the fluid plane, while flip-flop is slow due to the high energy barrier of the hydrophobic core.
Flashcard 17: What model describes membranes as a dynamic phospholipid bilayer with mobile proteins?
Answer: Fluid mosaic model. This model illustrates the plasma membrane as a flexible structure with phospholipids forming a fluid bilayer and proteins dispersed and mobile within it, reflecting its dynamic nature.
Flashcard 18: What is the primary role of cholesterol in animal cell membranes?
Answer: Buffers fluidity and decreases permeability to small polar solutes. Cholesterol intercalates between phospholipids to stabilize fluidity across temperature changes and tightens the bilayer to limit polar solute passage.
Flashcard 19: What property of transmembrane segments allows them to reside in the bilayer core?
Answer: Hydrophobic amino acids (often an b^1-helix). Nonpolar side chains in alpha-helical segments interact favorably with the hydrophobic bilayer interior, stabilizing the protein's position.
Flashcard 20: Which change to fatty acid tails decreases membrane fluidity at a given temperature?
Answer: Increase saturated fatty acid tails. Straight saturated chains pack more densely via van der Waals forces, reducing molecular movement and membrane fluidity.
Flashcard 21: What term describes the unequal distribution of lipids and proteins between the two leaflets?
Answer: Membrane asymmetry. Lipids and proteins are distributed differently in the inner and outer leaflets due to biosynthetic processes and functional requirements.
Flashcard 22: What are the orientations of phospholipid heads and tails in a plasma membrane bilayer?
Answer: Hydrophilic heads out; hydrophobic tails inward. Phospholipids self-assemble in aqueous environments to shield hydrophobic tails from water while exposing hydrophilic heads to the polar surroundings on both sides of the bilayer.
Flashcard 23: Which type of diffusion is typical for lipids and most membrane proteins within the bilayer plane?
Answer: Lateral diffusion. Lipids and proteins move freely sideways within the plane due to the fluid nature of the bilayer, allowing dynamic reorganization.
Flashcard 24: Where are carbohydrate chains located on plasma membrane glycoproteins and glycolipids?
Answer: On the extracellular (noncytosolic) surface. Carbohydrates are added in the ER and Golgi and oriented outward to participate in cell recognition and protection on the external face.
Flashcard 25: What is the glycocalyx?
Answer: Extracellular carbohydrate coat on the plasma membrane. The glycocalyx forms from oligosaccharides attached to membrane proteins and lipids, providing a protective layer and aiding in cell adhesion.