4971442
| Questão | Responda |
| What are the four types of membrane transport used by cells? | 1) Passive Transport ie Osmosis 2) Active Transport - uses ATP 3) Secondary Active Transport - uphill and downhill 4) Endo- & Exocytosis - for large molecules |
| Which ion channel is responsible for the plateau phase/prolonged action potential? | Ca2+ channel |
| At which voltages is the overshoot of an AP at? | Anything greater than 0 mV. |
| List two places where you would see Ca2+ channels in animals? | 1) Guinea Pig Atrium 2) Rabbit Node of Ranvier |
| What feature of an ion channel does the AP correlate with as described by Hodgkin and Huxley? | Permeability of the channel - ie ability of ions to cross channel |
| How does the concentration of ions affect AP? | The greater the difference in concentration the greater the AP |
| What is an aquaporin? | Membrane channel which only lets water through |
| What forms the basis of selectivity of the ion channel for passive transport? | Size and charge of the pore |
| What can membrane channels also function as? | Receptors - sense changes on the membrane and inside the cell |
| Give an example of a disease caused by a malfunction of aquaporin channels | Swelling of the brain. |
| What maintains the ionic gradient across a cell membrane? | Na+/K+ pump |
| What does the pump which maintains the ionic gradient require? | ATP |
| What is the ratio of ions across the Na+/K+ pump? | 3Na+ and 2K+ |
| What type of energy does the Na+/K+ pump store? What is it setting? | 1) Energy from hydrolysis of ATP is stored as ionic gradient 2) Sets a new gradient |
| What property does the Na+/K+ channel show? | Electrogenic property |
| What sets up the Na+/K+ channel? | Voltage gated K+ channel and leak channels |
| How do the Na+/K+ pump and voltage gated K+/leak channels relate? | Membrane potential is formed by repolarisation (ie by voltage gated K+ channels). Without Na+/K+ pump the gradient decays. |
| What is the typical range of RMPs? | -40 to -70mv |
| How is a typical membrane gradient orientated? | Negative from inside to out. |
| What is meant by the electrochemical gradient and equilibrium? | 1) Electrochemical gradient - gradient which an ion will move along based on the balance of concentration of that ion and the difference of charges across that membrane. 2) Equilibrium - the point at which there is no net flow of ions based on the balance of the concentration of ions and the charge. |
| What is capacitance? | Ability to store charge |
| What are the concentrations of Na+, K+ and Ca2+ inside and outside of cells? | Na+) O: 145mM I: 20mM K+) O: 4mM I: 150mM Ca2+) O: 2.5mM I: 1uM |
| What promotes resistance to flow? What can be done to reduce this? Which equation describes this? | 1) Lack of open channels 2) Increase the 'open probability' of channels 3) Ohm's Law - V=IR |
| What causes a pore to become semi-permeable? What then controls this? | A gate - mechanism which controls the open/closed configuration is the gating mechanism. |
| How do local anaesthetics work? What property do they show? | 1) Disrupt ion flow through channels - either block Na+ channels (hydrophilic) or bind to side of channel preventing function (hydrophobic) 2) Use dependence |
| Describe the stages which occur on the way to peak potential of an AP? | 1) Na+ enters cell, depolarisation 2) Na+ flows down concentration gradient towards equilibrium 3) VG Na+ channels start to open with depolarisation 4) If depolarisation reaches threshold many VG Na+ channels open causing AP 5) Concentration gradient decreases/shifts and Na+ ions get close to equilibrium |
| What happens after the peak of the AP is reached? | 1) +ve membrane potential causes K+ channels to open. 2) K+ flows out of cell causing repolarisation 3) Hyperpolarisation occurs. 4) Gradient stabilised and maintained by Na+/K+ pump |
| What are the physiological equilibrium potentials of: 1) Na+ 2) Ca2+ 3) K+ 4) Cl- | 1) +61mV 2) +137mV 3) -95mV 4) -65mV |
| Describe the Nernst Equation | Eion=RT/ZkF.ln[IONout]/[IONin] |
| What values would you use in the Nernst equation? For divalent ions? For anions? | 1) 58log10 at room temp 2) Divide by 2 3) Invert concentrations |
| How do membranes store charge? | Ion/charge separation - transmembrane electrical field. |
| Describe the Goldman-Hodgkin-Katz equation. What does is predict? Which Ions mainly determine this and why? | 1) Vm = 61.5log10(p[IONout]/[IONin] nb. as an anion this is reversed for Cl- 2) Predicts membrane potential. 3) Cl- and K+ as have highest permeability at RMP |
| What values do these markers stand for in Hodgkin and Huxley's numerical model: 1) n? 2) m? 3) h? | 1) Kinetic variable - which has voltage dependence 2) Activation variable 3) Inactivation variable |
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