Explain the meaning of the statement that phospholipids and most other membrane constituents are amphipathic molecules.
Membranes with different functions may differ in type and number of membrane proteins.
Membrane proteins are not very water-soluble.
Distinguish between peripheral and integral membrane proteins
List six major functions of membrane proteins.
Explain the role of membrane carbohydrates in cell-cell recognition (glycoproteins).
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.
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.
Distinguish between solutions that are hypertonic, hypotonic, and isotonic to cell contents.
Define osmosis and predict the direction of water movement based on differences on solute concentrations.
Explain how transport proteins facilitate diffusion.
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.
Explain how an electrogenic pump creates voltage across a membrane. Name two electrogenic pumps.
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?
Distinguish between exocytosis and receptor-mediated endocytosis.
Explain how cholesterol resists changes in membrane fluidity as temperatures change.
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.
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