Explain the meaning of the statement that phospholipids and most other membrane constituents are amphipathic molecules.
Most molecules are amphipathic molecules because phospholipids are both hydrophobic and hydrophilic on the bilayer, due to the heads being hydrophilic and tails being hydrophobic.
Membranes with different functions may differ in type and number of membrane proteins.
Each membrane has its own unique complement of membrane proteins, which determine most of the specific functions of that membrane.
Membrane proteins are not very water-soluble.
Membrane proteins are not very water-soluble because they are impermeable to most hydrophilic molecules.
Distinguish between peripheral and integral membrane proteins
Peripheral: Provides the framework for the plasma membrane and is
attached to integral protein.
Integral: Go through the membrane
with two hydrophilic ends.
List six major functions of membrane proteins.
1. Transport
2. Enzymatic activity
3. Cell-cell
recognition
4. Intercellular joining
5. Signal
transduction
6. Attachment to the cytoskeleton and extracellular matrix
Explain the role of membrane carbohydrates in cell-cell recognition (glycoproteins).
The ability of a cell to distinguish other cells based on recognition of membrane carbohydrates. The glycolipids and glycoproteins attached to the outside of plasma membranes varies.
Explain how hydrophobic molecules cross cell membranes.
Cell membranes are made of a lipid bilayer, molecules with hydrophilic heads and hydrophobic tails. These molecules arrange in parallel lines with the tails facing inwards towards each other and the heads facing outwards towards the water. Hydrophobic molecules are drawn into the lipid bilayer, trying to get away from the water.
Distinguish between channel proteins and carrier proteins.
Channel proteins: Hydrophobic pathways through a membrane are provided for specific molecules, such as aquaporins, which facilitate water passage.
Carrier proteins: Physically bind and transport a specific molecule.
Define diffusion. Explain why diffusion is a passive and spontaneous process.
Diffusion: The movement of a substance down its concentration gradient due to random thermal motion.
Diffusion is a passive and spontaneous process because one solute is unaffected by the concentration gradients of other solutes and the cell does not expend energy when substances diffuse down their concentration gradient.
Explain why a concentration gradient of a substance across a membrane represents potential energy.
The concentration gradient of a substance across a membrane represents potential energy because it drives diffusion.
Distinguish between solutions that are hypertonic, hypotonic, and isotonic to cell contents.
Hypertonic: When the cell loses water and shrivels.
Hypotonic: When the cell gains too much water, swell, and possibly lyse (burst).
Isotonic: Equilibrium; when the cell neither gains or lose water.
Define osmosis and predict the direction of water movement based on differences on solute concentrations.
Osmosis: The diffusion if water across a selectively permeable membrane.
The direction of water movement based on differences on solute concentrations depends on how the water diffuses down its own concentration.
Explain how transport proteins facilitate diffusion.
Transport proteins aids the diffusion of ions and polar molecules to move across the plasma membrane.
Distinguish between osmosis, facilitated diffusion, and active transport.
Osmosis: The diffusion if water across a selectively permeable membrane.
Facilitated diffusion: The diffusion of polar molecules and ions across a membrane with the aid of transport proteins, with either channel proteins or carrier proteins.
Active transport: The movement of a substance across a cell membrane, with an expenditure of energy, against its concentration or electrochemical gradient; mediated by specific transport proteins.
Describe the two forces that combine to produce an electrochemical gradient.
Combination of chemical force (the ion's concentration gradient) and electrical force (the effect of the membrane potential on the ion's movement).
Explain how an electrogenic pump creates voltage across a membrane. Name two electrogenic pumps.
Active transport and sodium-potassium pump
Describe the process of cotransport
A mechanism through which the active transport of solute is indirectly driven by an ATP-powered pump that transports another substance against its gradient. As that transported substance then diffuses back down down its concentration gradient through a contransporter, the solute is carried against its concentration gradient across the membrane.
How are large molecules are transported across a cell membrane?
The process of exocytosis secretes large molecules by the fusion of vesicles with the plasma membrane.
Distinguish between exocytosis and receptor-mediated endocytosis.
Exocytosis: The cell secretes large molecules by the fusion of vesicles with the plasma membrane.
Receptor-mediated endocytosis: Allows a cell to acquire specific substances from extracellular fluid.
Exocytosis
The cell secretes large molecules by the fusion of vesicles with the plasma membrane.
Endocytosis
A region of the plasma membrane sinks inward and pinches off to form a vesicle containing material that had been outside the cell.
Phagocytosis
A form of endocytosis in which pseudopodia wrap around a food particle, creating a vacuole that then fuses with a lysosome containing hydrolytic enzymes.
Proton pump
Transports H+ out of the cell generates voltage across membranes on plants, fungi, and bacteria.
Explain how cholesterol resists changes in membrane fluidity as temperatures change.
At moderate temperatures, cholesterol hinders fluidity but at colder temperatures, it can lower the temperature at which a membrane solidifies since it hinders the phospholipids in forming the pack arrangement.
Describe the fluidity of the components of a cell membrane and explain how membrane fluidity is influenced by temperature and membrane composition.
The cell membrane moves in a lateral motion. The membrane maintains its fluidity even though the temperature decreases until it reaches a certain temperature and solidifies. Also, there are kinks in the hydrophobic tails of unsaturated phospholipid tails which cause the membrane to have more fluidity than membranes mostly consisting of saturated phospholipid tails.
Explain how aquaporins facilitate the passage of water through membranes.
Aquaporins allows entry of up to 3 billion water molecules per second and if they did not exist, only a fraction of that amount would diffuse into the same area therefore aquaporins facilitate the passage of water since it lets in most of the water molecules in the cell membrane.
Describe how living cells with and without cell walls regulate water balance.
Living cells without cell walls regulate water balance by either residing in an isotonic area or by having adaptations that help the process of regulating water balance (called osmoregulation). Cells with cell walls also let water flow into the cell until it reaches a certain extent and the cell wall exerts a backward pressure which forces the water out.
Explain how the binding of oxygen to hemoglobin illustrates cooperativity
One oxygen atom will bond to one of the for active sites of hemoglobin. This is cooperativity because it keeps the hemoglobin in the active state and increases the affinity of oxygen to the enzyme.
carbohydrate
A sugar (monosaccharide) or one of its dimers (disaccharides) or polymers (polysaccharides)
phospholipid
A molecule that is a constituent of the inner bilayer of biological membranes, having a polar, hydrophilic head and a nonpolar, hydrophobic tail