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12-1

12-1. K + is high inside cells, Na + is high outside because of the Na+/K+ ATPase (the sodium pump). Energy is stored in the electrochemical gradient :

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12-1

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  1. 12-1 • K+ is high inside cells, Na+ is high outside because of the Na+/K+ ATPase (the sodium pump). • Energy is stored in the electrochemical gradient: • the chemical and electrical forces across the membrane that arise from the asymmetric distribution of charges and ion concentrations • The intracellular pH is slightly lower than outside. • Cells take great pains to keep cytoplasmic [Ca++]very low.

  2. Changes in membrane potential are used by neurons for electrical signalling The actual number of ions that move is small: 1/100,000th of the concentration can change the membrane potential, Vm by 100mV in a typical cell, so ion concentrations are not measurably affected during electrical signalling in neurons.

  3. substituting: (z=1) For ions moving down concentration gradient, ∆G<0 Chemical forces: The free energy change for one mole of ions moving across a membrane: ∆Gconc = –RT ln Co/Ci Electrical forces: The free energy change for charged ion movement: ∆Gvolt = zFV At equilibrium, the chemical and electrical forces balance: ∆Gvolt + ∆Gconc = 0

  4. ion-selective K+ channel K+ K+ chemical force electrical force Cl– + – – + + – – + by convention Vm = Vin – Vout 100mM K+Cl– 10mM K+ Cl– VeqK+ = 58mV•Log10Co/Ci VeqK+ = 58mV•Log10Co/Ci = –58mV

  5. ion-selective K+ channel 10mM Na+Cl– 100mM Na+Cl– ion-selective Na+ channel Veq = 58mV•Log10Co/Ci VeqK+ = 58mV•Log10Co/Ci = –58mV 100mM K+Cl– 10mM K+Cl– by itself VeqNa+ = 58mV•Log10Co/Ci = 58mV Both channels together: Na+ in, K+ out; at steady state inward and outward currents match. What will the resting membrane potential (Vm) be?

  6. 10mM K+Cl– 100mM K+Cl– conformation may change to open and close gated channel 100mM Na+Cl– 10mM Na+Cl– The resting potential depends on how fast ions flow through each channel, the relative conductance. Since the concentration gradients do not change, the membrane potential can be set anywhere between –58 and +58mV simply by changing the ratio between sodium and potassium conductances, i.e., by opening and closing channels.

  7. Chemiosmotic coupling Energy is stored in theelectrochemical gradient: the chemical and electrical forces across the membrane that arise from the asymmetric distribution of charges and ion concentrations Mitochondria use energy from electrons (e–) to pump protons (H+) across a membrane and then use the electrochemical gradient to make ATP.

  8. The resting potential for most cells is negative (–20 to –200mV) because real cells are permeable to both K+ and Cl–, but have low Na+ permeability. K+ would flow out (conc. gradient) and Cl– in (due to Vm and intracellular anions), and H2O would flow in. However, the driving force for Na+ in is high, driving Vm 0. Counteracting this is the electrogenic Na+/ K+ATPase.

  9. Proton-motive force Electrical forces: The free energy change for charged ion movement: ∆Gvolt = zFVm are large compared to Chemical forces: The free energy change for one mole of ions moving across a membrane: ∆Gconc = RT ln Cmatrix/Ccytosol The Nernst Equation Electrical forces ∆pH= pHmatrix – pHcytosol pmf = Vm + 2.3RT ∆pH/F Chemical forces

  10. Proton-motive force is used to drive ATP synthesis inner membrane ATP synthase can go backwards and hydrolyze ATP

  11. Oxidative phosphorylation ATP synthase - an amazing machine! 100 ATPs per second 1 ATP for 3 H+

  12. ATP synthase

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