9.0 Asn 2.1 19. The pl of an amino acid is the pH at which it has a zero net cha
ID: 208166 • Letter: 9
Question
9.0 Asn 2.1 19. The pl of an amino acid is the pH at which it has a zero net charge. Using the data above, calculate the pl of ASN. (2 pt) Titranon of an amino aad 14.00 12.00 10 00 8 00 6 00 4 00 2.00 1 0 2.0 3.0 4 0 added NaOH (mol) 20. From the titration plot above, which points on the graph represent pk's? (2 pt) a. 1 and 7 b. 2, 4 and 6 c. 3 and 5 d. 2, 3, 4, 5 and 6 e. The pKs cannot be determined without more information. 21. From the titration plot above, which point most likely represents the pK for the carboxyl group? (2 pt) a. 1 b. 2 c. 3 d. 4 e. 5Explanation / Answer
19) pI=5.55
The isoelectric point is the point at which amino acid exists as a neutral form. When the pH of solution less than the pI of amino acid then it exist as a cation and when the pH of solution greater than the pI the amino acid then it exists as an anion and when pI equals to pH then protein acid exist as neutral form.
Isoelectric point of Aspargine: the isoelectric point is the point at which amino acid exists as a Zwittor ion or neutral form
pI= pK1+pK2 /2
Where pK1 is pKa value of –COOH group
pK2 is pKa value of –NH2 group
pI = 2.1+9.0/2
=5.55
20) If we consider it as Aspargine then the pK’s are point 2 and point 5 (answer not in given options)
Molecular species which have both positive and negative charges in its structure than that Molecular species is called Zwittor ion. The Zwittor ion is electrically neutral and dipolar ions.
e.g. +NH3-CH (CH3)-COO-
pK1 defined as the pH at which 50% of amino acid in cation form and 50% of amino acid in Zwittor ion form.
pK2 defined as the pH at which 50% of amino acid in anion form and 50% of amino acid in Zwittor ion form.
Amino acid show maximum buffering action around pK values and minimum at pI values.
We need more information to determine the pk values exactly
21) pk for carboxyl gruop is (b) 2
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