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What is the isoelectric point for cysteine?
Information given in table:
pKa COOH (1.9) pKa NH3 (10.3) pKa R group (8.4).
Answer: 5.2. The isoelectric point is found by averaging the pKas that give a +1 charge to the molecule and a -1 charge to the molecule. Thus from the table values, pI = 1.9+8.4/2 = 10.3/2 = 5.15.
I understand that the isoelectric point is where zwitter ion exist and that it is where the +1 -1 charge is aka a neutral molecule, but how did they know which pKas to use? I just averaged the pKas of COOH and NH3. How did they know to use pKa of R group and pKa of COOH.
So confused! Thank you
Information given in table:
pKa COOH (1.9) pKa NH3 (10.3) pKa R group (8.4).
Answer: 5.2. The isoelectric point is found by averaging the pKas that give a +1 charge to the molecule and a -1 charge to the molecule. Thus from the table values, pI = 1.9+8.4/2 = 10.3/2 = 5.15.
I understand that the isoelectric point is where zwitter ion exist and that it is where the +1 -1 charge is aka a neutral molecule, but how did they know which pKas to use? I just averaged the pKas of COOH and NH3. How did they know to use pKa of R group and pKa of COOH.
So confused! Thank you