Question

At physiological pH, what is the approximate net charge of a hexapeptide with

the following amino acid sequence: Asp-Val-Ile-Glu-Arg-Ser

A. -2
B. -1
C. 0
D. +1
E. +2

Answer 1

The net charge of the hexapeptide sequence Asp-Val-Ile-Glu-Arg-Ser at physiological pH is -1, considering the negative charges from Asp and Glu, and the positive charge from Arg.

Step-by-step explanation:

The net charge of a hexapeptide at physiological pH, which is usually around 7.4, can be determined by looking at the charged groups in its amino acids. To find the net charge, we have to consider the individual amino acids' side chains and their pKa values. The hexapeptide sequence given is Asp-Val-Ile-Glu-Arg-Ser.

• Aspartic acid (Asp) has a side chain with a pKa of approximately 3.9 and will be negatively charged at physiological pH.
• Glutamic acid (Glu) also has a side chain with a pKa of about 4.1 and will be negatively charged at physiological pH.
• Arginine (Arg), a basic amino acid, has a side chain with a pKa of 12.5 and will be positively charged.
• Valine (Val), Isoleucine (Ile), and Serine (Ser) have neutral side chains at physiological pH.

The net charge is therefore the sum of the charges of the individual amino acids: two negative charges (from Asp and Glu) and one positive charge (from Arg). Thus, the net charge would be -2 + 1 = -1.

Given the choices, the approximate net charge of the hexapeptide at physiological pH is -1.