# Shared Flashcard Set

## Details

05
Biophysics I
30
Pharmacology
12/27/2016

Term
 State Ohm's Law
Definition
 electric current is proportional to voltage and inversely proportional to resistance (in a circuit)I = GV G = 1/R I = V/RI=current, G=conductance, R=resistance, V=voltage
Term
 Define equilibrium potential
Definition
 membrane potential where the net flow through any open channel is 0. The chemical and electrical forces are balanced.
Term
 Give the Nersnt equation at 37°C
Definition
 Ex = 6.1log([X]o/[X]i)
Term
 What does the Nersnt equation show?
Definition
 gives a formula that relates the numerical values of the concentration gradient to the electrical gradient that balances it
Term
 Give the intracellular and extracellular concentrations of K+ in mammalian skeletal muscle and the equilibrium potential
Definition
 intracellular: 155mMextracellular: 4mMequilibrium potential: -98mV
Term
 Give the intracellular and extracellular concentrations of Na+ in mammalian skeletal muscle and the equilibrium potential
Definition
 intracellular: 12mMextracellular: 145mMequilibrium potential: +67mV
Term
 Give the intracellular and extracellular concentrations of Cl- in mammalian skeletal muscle and the equilibrium potential
Definition
 intracellular: 4.2mMextracellular: 123mMequilibrium potential: -90mV
Term
 Give the intracellular and extracellular concentrations of Ca2+ in mammalian skeletal muscle and the equilibrium potential
Definition
 intracellular: 0.0001mMextracellular: 1.5mMequilibrium potential: +110mV
Term
 Give the Nernst equation for any temperature
Definition
 Ex = (RT/zF)ln([X]o/[X]i)
Term
 How does the Nernst equation change for Na+?
Definition
 It doesn't.
Term
 How does the Nernst equation change for K+?
Definition
 It doesn't.
Term
 How does the Nernst equation change for Ca2+?
Definition
 Ca2+ has divalency, therefore a '2' is before Faraday's constant (F)
Term
 How does the Nernst equation change for Cl-?
Definition
 Cl- has an inverted ratio as it is negatively charged.
Term
 When is the GHZ equation used?
Definition
 to calculate composite membrane potential by incorporating different ions
Term
 Describe ion channels
Definition
 - selective- conduct small ionic currents along the electrochemical gradient- open/close in milliseconds
Term
 Describe transporters/exchangers
Definition
 - integral membrane proteins- move along electrochemical gradient- binding/releasing ion- do not normally conduct electrical current
Term
 Describe ion pumps
Definition
 - against electrochemical gradient- takes up ATP- Examples: Na+/K+ ATPase, PMCA (plasma membrane Ca2+ ATPase).
Term
 Calculate the membrane potential if the membrane is mainly permeable to K+ ions but also has small permeability to Na+ (PK = 0.935; PNa = 0.065)
Definition
 see lecture
Term
 If the cell is permeable only to K+ what is the membrane potential? 2. External K+ is changed to 10 mM. What is the new membrane potential? 3. External K+ is changed to 20 mM. What is the new membrane potential? 4. Suppose the cell is now only permeable to Na+, what is the membrane potential? 5. External Na+ is changed to 70 mM. What is the membrane potential? 6. External Na+ is changed to 40 mM. What is the membrane potential?7. If the cell is only permeable to Cl-, what is the membrane potential? 7. External Cl- is reduced to 70 mM. What is the membrane potential? 8 External Cl- is increased to 200 mM. What is the membrane potential?
Definition
 see lecture
Term
 Describe the structure of voltage-gated ion channels
Definition
 - Voltage-gated ion channels have an ion conducting pore and a gate(s) controlling the pore.- The pore has a region called a selectivity filter that allows permeable ions to go through much easier than the other ions.- The gate is coupled to a voltage sensor: a moveable portion of the protein molecule that is sensitive to changes in voltage across the membrane.
Term
 How does movement of the voltage sensor control the ion channel gate?
Definition
 - when the gate occludes the channel pore, the channel is closed.- the gate opens due to a conformational change in the structure of thechannel protein brought about by the voltage sensor. When the gate opens, the ion channel conducts ionic current.
Term
 When do most voltage-gated channels open?
Definition
 Most voltage-gated channels are closed at resting membrane potential, but will open upon depolarisation.
Term
 Describe the structure of voltage-gated sodium channels
Definition
 Sodium channels consist of a large α-subunit that associates with other proteins, such as β-subunits. An α-subunit forms the core of the channel and is functional on its own. When a cell expresses the α-subunit protein, it is able to form channels that conduct Na+ in a voltage-gated way, even if β-subunits or other known modulating proteins are not expressed.
Term
 Describe the structure of the α-subunit
Definition
 The α-subunit has four repeat domains, labelled I through IV, each containing six membrane-spanning segments, labelled S1 through S6. The highly conserved S4 segment acts as the channel's voltage sensor.
Term
 What are voltage-dependent Ca2+ channels formed by?
Definition
 Voltage-dependent Ca2+ channels are formed as a complex of several different subunits: α1, α2δ, β1-4, and γ. The α1 subunit forms the ion-conducting pore while the associated subunits have several functions including modulation of gating (Dolphin, A.C. (2003)).
Term
 How are K+ channels selective to K+ when Na+, still a monovalent ion, is even smaller in size than K+ so should pass through easily?
Definition
 The Na+ channel just has a smaller pore, so it’s easy to understand why Na+ channels are selective for Na+ and don’t allow K+ through – it just doesn’t fit (too fat).
Term
 What gates are involved in Na+ channels?
Definition
 1. activation gate2. inactivation gate ('h' gate)
Term
 Describe the activation gate
Definition
 The activation gate– ‘m ’gate – opens rapidly upon depolarisation and allows Na+ to flow through, into the cell.
Term
 Describe the inactivation gate
Definition
 The inactivation gate– ‘h’ gate –also responds to depolarisation and plugs the channel pore therefore preventing ion flow (after a delay of around 5ms).The ‘h’ gate remains in place for the duration of the refractory period. For this short time, further Na+ entry is not possible.
Term
 Why is the resting potential membrane 0?
Definition
 biological membranes have ion channels, transporters and pumps that together create asymmetric distribution of ions across the plasma membrane.
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