A purified protein is in a HEPES (N-(2-hydroxyethyl)piperazine-N-(2-ethanesulfon

Question

A purified protein is in a HEPES (N-(2-hydroxyethyl)piperazine-N-(2-ethanesulfonic acid)) buffer at pH 7 with 400 mM NaCl. A sample (1 mL) of the protein solution is placed in a tube made of dialysis membrane and dialyzed against 1.0 L of the same HEPES buffer with 0 mM NaCl. Small molecules and ions (such as Na, Cl, and HEPES) can diffuse across the dialysis membrane, but the protein cannot. Once the dialysis has come to equilibrium, what is the concentration of NaCl in the protein sample? Assume no volume changes occur in the sample during the dialysis. Number b If the original 1 mL sample were dialyzed twice, successively, against 200 mL of the same HEPES buffer with 0 mM NaCI, what would be the final NaCI concentration in the sample? Number NaCi- mM O Previous Give Up & View Solution check Answer 0 Next Exit Hin

Explanation / Answer

Dialysis is done to seperate the molecules like salts from protein samples.The movement of molecules is from higher concentration of solutes to the region of lower concentration.When the concentration on both sides remain same then equilibrium is said to be achieved.

a.Thus at equilibrium the concentration of sodium chloride will be 200mM.Also the sample taken is 1 ml.Here even the sample volume is 1 ml the concentration of NaCl will remain same that is 400mM.

b.if the sample is dialysed twice then during first dialysis the concentration will be 200mM even if the buffer volume is less(200ml).During second successive dialysis again the concentration will be halfed that is 100mM.

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