The isoelectric point of a molecule can be calculated from the pKa values of its ionisable groups.Calculate the isoelectric point of the molecule below. Give your answer to one decimal point.

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To determine the isoelectric point (pI) for this molecule, we first identify the ionizable groups and their pKa values shown in the diagram. The molecule has two carboxyl groups (with pKa values 2.1 and 3.7) and one amine group (with pKa 9.8). For amino acids that are acidic (like aspartic acid), the pI is calculated as the average of the pKa values of the two groups that lose protons last before the molecule becomes neutral at its pI. In this case, the two groups that are deprotonated around the pI are the two carboxyl groups (the side-chain and the terminal carboxyl). Therefore, we average 2.1 and 3.7.

Step 1: Identify the relevant pKa values for the pI calculation: 2.1 and 3.7 (the two carboxyl groups).
Step 2: Compute the average: (2.1 + 3.7) / 2 = 5.8 / 2 = 2.9.
Step 3: Round to one decimal place as requested: 2.9.

Thus, the isoelectric point of the molecule is 2.9. The other pKa values (9.8 for the amino group) are not used in this acidic amino acid pI calculation because they pertain to deprotonation events that occur at higher pH and do not determine the zero-net-charge point for this species.

My LMS Subjects Quiz 3

The isoelectric point of a molecule can be calculated from the pKa values of its ionisable groups.Calculate the isoelectric point of the molecule below. Give your answer to one decimal point.

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