Multiple Choice
Which of the following is considered the fastest-acting buffering mechanism in the human body?
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2. Water
Buffer Solution
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Given four proteins with isoelectric points (pI) of 4.5, 6.0, 7.5, and 9.0, at which buffer pH would exactly two of the proteins adhere to a cation-exchange column?
A
pH 7.0
B
pH 6.5
C
pH 4.0
D
pH 9.5
Verified step by step guidance1
Understand the principle of cation-exchange chromatography: Proteins bind to a cation-exchange column when they are positively charged. A protein's charge depends on the pH of the buffer relative to its isoelectric point (pI). At a pH below its pI, a protein is positively charged; at a pH above its pI, it is negatively charged.
Analyze the isoelectric points (pI) of the given proteins: The proteins have pI values of 4.5, 6.0, 7.5, and 9.0. At a pH below their pI, they will be positively charged and adhere to the cation-exchange column. At a pH above their pI, they will be negatively charged and not adhere.
Evaluate the buffer pH options provided: pH 7.0, pH 6.5, pH 4.0, and pH 9.5. For each pH, determine which proteins will be positively charged (pH < pI) and adhere to the column.
For pH 7.0: Proteins with pI values of 7.5 and 9.0 will be positively charged and adhere to the column, while proteins with pI values of 4.5 and 6.0 will be negatively charged and not adhere.
Conclude that at pH 7.0, exactly two proteins (pI 7.5 and pI 9.0) adhere to the cation-exchange column, making it the correct answer.
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