Biology Practice Problems Proteins Practice Problems Solution: What is the charge of the tetrapeptide Lys-Lys-His...

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Solution: What is the charge of the tetrapeptide Lys-Lys-His-Glu at pH 7?A. +2B. 0C. -2D. +1E. -1

Problem

What is the charge of the tetrapeptide Lys-Lys-His-Glu at pH 7?

A. +2

B. 0

C. -2

D. +1

E. -1

Solution

The charge of proteins and polypeptides would depend on the condition of the dissociable protons along the chain. These include the protons in the C terminal, the N terminal, and the side chains. 

The protons in the C terminal and in the acidic side chains dissociate at pH lower than 7. This leaves a negative charge from each of those substituents. Meanwhile, the protons in the N terminal and those of the basic side chains dissociate at pH above 7. As long as these protons are attached to those basic groups, they will have a + charge per substituent. 

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