Final answer:
The isoelectric point of the polypeptide Ala-Lys-Asp-Arg-Val-Ile-Glu is likely higher than neutral due to the presence of more basic than acidic residues, making option c) 9.5 the most plausible answer.
Step-by-step explanation:
The isoelectric point (pI) of a polypeptide is the pH at which the polypeptide carries no net charge. To determine the isoelectric point of the polypeptide Ala-Lys-Asp-Arg-Val-Ile-Glu, one must consider the individual pI values of the acidic and basic amino acids present. Basic amino acids like lysine (Lys) and arginine (Arg) typically have higher pI values, whereas acidic amino acids like aspartic acid (Asp) and glutamic acid (Glu) have lower pI values.
As this polypeptide contains both acidic and basic amino acids, the overall isoelectric point will be a balance between these. Without precise pKa values for the side chains and the N-terminus and C-terminus, it is not possible to calculate the exact pI. However, because there are more basic (positively charged) residues than acidic (negatively charged) residues in this peptide, the isoelectric point is likely to be higher than neutral pH 7, making options b) 7.5 and c) 9.5 more plausible than option a) 6.0. Furthermore, given the strong basicity of the lysine and arginine residues, the isoelectric point is more likely to be towards the basic end of the pH scale. Although option d) 10.0 is theoretically possible, it is less likely due to the presence of the acidic residues, which would lower the pI slightly from the basic amino acid pI values. Therefore, the most likely answer, without exact calculation, would be c) 9.5.