694659
| Question | Answer |
| major memebrane system of eukaryotic cells | plasma membrane - phospholipid polymers of fatty acids, glycerol, phosphate and a terminal amine or alcohol group -amphipathic molecules -spontaneously form monolayers and bilayers |
| Major functions of cell membranes | -to compartmentalize metabolic activities - to separate/protect cellular components -to provide a ‘scaffold’ for signalling -as a medium for cellular energy generation (Compartmentalization, protection and energy generation arises from the immiscibility of water and membranes) |
| membrane charges | Diffusion can generate a small imbalance in ion (charge)concentrations A membrane voltage (electrical charging) occurs when (i) immobile charges are not balanced (ii) charge transport is not fully balanced |
| chemical and electrical gradients | The Nernst Equation describes the equilibrium between chemical and electrical forces |
| Nerst equation | 9 |
| transport proteins | create a hydrophilic passage. create a filter. provide possibility for energy coupling. provide possibility for regulation. |
| Facilitated diffusion | Transport proteins create a hydrophilic pore Molecules diffuse through this pore Example: water channel (aquaporin) |
| forces drive the movement of molecules | Chemical gradient = concentration gradient Electrical gradient = charge gradient Only relevant for char ged molecules (ions). |
| cations | Proton H+ Potassium K+ Ammonium NH4 + Histidine Spermidine |
| anions | cholride nitrate glutamate malate pyruvate |
| The electrochemical gradient | = the net driving force for the movement of a molecule resulting from the combination of the chemical and electrical gradient. |
| Active transport | moves substances against the electrochemical gradient. It requires the input of energy. |
| Passive transport | moves substances down the electrochemical gradient. It requires no input of energy. |
| Transport proteins for active transport | Pumps Co-transport systems |
| Transport proteins for passive transport | Channels Carriers |
| pumps | energy coupling; ATPases couples to hydrolysis of ATP conformational change e.g sodium/potassium pump proton pump calcium pump |
| Co-transport systems | Co-transporters couple the downward movement of one ion to the uphill movement of another solute. symport- Driver ion and substrate move in the same direction antiport- Driver ion and substrate move in the opposite direction |
| channel | A channel provides an aquous pore for the passage of ions |
| carrier | A carrier undergoes a conformational change that exposes ion binding sites to different sides of the membrane. |
| ion channels | selective gated |
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