3 Flashcards
What is the primary role of the plasma membrane?
It serves as a boundary that separates the living cell from its nonliving surroundings and exhibits selective permeability.
Describe the structure and properties of phospholipids in the plasma membrane.
Phospholipids are amphipathic molecules with hydrophobic (tail) and hydrophilic (head) regions, forming a phospholipid bilayer.
What is the fluid mosaic model?
Proposed by Singer and Nicolson, it describes membranes as fluid structures with a mosaic of various proteins embedded in the lipid bilayer.
How do phospholipids move within the plasma membrane?
Phospholipids can drift laterally within the bilayer, but flipping between leaflets is rare and facilitated by enzymes like flippase and floppase.
What factors influence the fluidity of membranes?
Temperature and lipid composition; membranes rich in unsaturated fatty acids are more fluid than those with saturated fatty acids.
Explain the role of cholesterol in membrane fluidity.
Cholesterol stabilizes membrane fluidity by restraining phospholipid movement at high temperatures and preventing tight packing at low temperatures.
What are the major functions of membrane proteins?
Functions include cell-cell recognition, intercellular joining, attachment to the cytoskeleton and ECM, transport, enzymatic activity, and signal transduction.
Distinguish between passive transport and active transport.
Passive transport moves substances down their concentration gradient without energy (e.g., diffusion), while active transport moves substances against their gradient, requiring energy (e.g., ATP)
Describe osmosis and its impact on cell water balance.
Osmosis is the diffusion of water across a selectively permeable membrane, driven by solute concentration differences, affecting cell volume based on tonicity (hypertonic, hypotonic, isotonic).
What is facilitated diffusion?
Facilitated diffusion involves transport proteins that assist the movement of molecules across the plasma membrane without using energy.
Explain the sodium-potassium pump’s mechanism.
This active transport system exchanges Na⁺ and K⁺ across the membrane, utilizing ATP to change the conformation of the pump, moving sodium out and potassium in against their gradients
Define cotransport and provide an example.
Cotransport occurs when the active transport of one solute drives the transport of another; e.g., the H⁺ gradient created by proton pumps driving nutrient uptake in plants.
What are the three types of endocytosis?
Phagocytosis (cellular eating), pinocytosis (cellular drinking), and receptor-mediated endocytosis (ligand binding triggers vesicle formation).
Describe exocytosis and its significance in cellular function.
Exocytosis is the process of moving materials from inside the cell to the exterior, often used by secretory cells to export products like hormones or neurotransmitters.
How does the concentration gradient affect diffusion?
Molecules tend to move from areas of higher concentration to lower concentration until dynamic equilibrium is reached, with no energy required for this process.
