Question

Draw the peptide ATLDAK. (a) Calculate its approximate pI. (b) What is its net charge at pH 7.0?

Short answer

a) The required approximate value of pI is $\text{5.95}$.

b) The net charge at pH 7.0 is 0.

Step-by-step solution

Concept introduction

pH is a scale used in chemistry to measure the acidity or basicity of an aqueous solution. pH originally stood for "potential of hydrogen." The pH of acidic solutions is lower than that of basic or alkaline solutions

Calculating the approximate value of pI

(a)The structure of peptide ATLDAK is:

The ionisable side chains have pK values of$\text{3.9}$ and$\text{10.5}$ . Lys's terminal carbon group has a pK of, while Ala's terminal amino group has a pK of$\text{8.0}$.

The pl value is situated in the middle of the two ionizations involving neutral species.

$$\begin{gathered} \text{pl = 1/2(3.9 + 8.0)} \\ \text{= 5.95 (approx.)} \end{gathered}$$

Therefore, the required approximate value of pI is $\text{5.95}$.

Finding the netcharge at pH 7.0

(b)At pH 7.0, the net charge is 0. The number of protons and electrons are equivalent if the molecules of ionizable side chains are calculated and compared.