13. Compare the free energy required to move one mol of Na ions from the outside

Question

13. Compare the free energy required to move one mol of Na ions from the outside to the inside of the cell when the membrane potential is – 70mV versus –20 mV Under WHICH conditions, ie at which membrane potential, would you expect the rate of transport of Na ions to be faster, and WHY ????

14. Two transmembrane proteins with very small amino terminal or carboxyterminal domains as well as small inter-transmembrane loops are being purified. ONE is composed of 5 alpha-helical domains, and the other of 5 beta strands. Which of these proteins, after extraction into a non-denaturing detergent, would likely elute first from a size-exclusion column? WHY ????

Explanation / Answer

13. For calculating the free energy of Na+ ions moving from outside to inside.

Delta Gc= RT In Nain/Naout

The free energy change generated from the membrane electric potential is given by

Delta G= FE

where F is the Faraday constant and E is the membrane electric potential

Delta G= 23,062 cal/(mol · V) x -70mV= -1.6 Kcal/mol

Delta G= 23,062 cal/(mol · V) x -20mV= -0.46 Kcal/mol

Since G is <0, the inward movement of Na+ ions is thermodynamically favored. So at -70mV the rate of Na ions to be faster. More the negative delta G, more it is favorable thermodynamically.

14. These types of membrane proteins are called integral transmembrane proteins. These proteins have a hydrophobic transmembrane domain mainly composed of either alpha helix or beta sheets. The structure is very stable due to the hydrophobic interactions with the lipid bilayer. Both the transmembrane proteins extracted into the nondenaturing detergent will be in their intact form which will give them equal molecular weight. So both the proteins will elute at the same time from the column.

Related Questions

Navigate

• Browse (All)
• Browse 1
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.