11. Thermodynamics 4

Question 1

What is another major interconversion of electrical and chemical potential energies which occur across membranes?

Answer 1

Membrane potential

Prokaryotes and eukaryotes: Across cell membranes + also membrane potentials across the membranes in cellular organelles such as mitochondria

Question 2

How do mitochondria interconvert electrical potential energy and chemical potential energy?

Answer 2

Use redox reactions during the electron transport chain

Electron flow form spatially separated redox half-reactions

Used to power proton pumps= Generate membrane potential which is used as an energy source to power ATP synthesis

Inside= Negative 
Outside= Positive 

Positive ions are attracted to the inside of the membrane= Potential energy from the force that is pulling the positive sodium ion inside

Question 3

What are the 2 factors involved in moving ions across membranes?

Answer 3

1) The relative concentrations of the ion on either side of the membrane= Ions move from high concentration to low concentration
2) The electrical potential across the membrane= Ions are electrostatically repelled by the same charge and are attracted to the opposite charge

Question 4

What needs to happen to the position of the equilibrium for a membrane to selectively be permeable to a specific ion?

Answer 4

The free energy resulting from the concentration inequality EXACTLY balances the free energy due to the electrostatic potential difference

Question 5

Which equation can be used to predict the potential difference of the diffusion of an ion across the cell membrane?

Answer 5

Nernst equation: 
ΔE = (RT / ZF) ln ( [Ion(outside)] / [Ion(inside)] ) 
where: 
ΔE is the potential in volts
Z is the charge on the ion (= +1)
R is the gas constant (8.314 J mol-1),
T is the temperature (°K), 
F is the Faraday constant (96500 J mol-1 V-1)

Equation is written with the concentration of ion outside on TOP and inside on the BOTTOM= Inside relative to outside

The energy measured is different to actual value due to contributions of other ions

Question 6

What is the equation for working out the overall free energy change when an ion of charge Z is moved across a cell membrane from outside to inside?

Answer 6

ΔG = RT ln { Cin / Cout } + ZF ΔE J mol–1

Cin/Cout= Concentration ratio