a. What is the net charge on valine at pH 1?
b. at pH 7?
c. at pH 14?
To determine the net charge on valine at different pH levels, we first need to understand the properties of valine. Valine is an amino acid, and its charge depends on the ionization of its functional groups - the carboxyl group (COOH) and the amino group (NH2).
a. At pH 1:
At very acidic pH levels, the concentration of H+ ions is high. In this case, the carboxyl group (COOH) will be protonated (loses a hydrogen ion, H+) and become COOH2+, while the amino group (NH2) will remain protonated (NH3+). Therefore, the valine molecule will have a net charge of +1.
b. At pH 7:
At neutral pH, the concentration of H+ ions is relatively low. The carboxyl group (COOH) will lose its proton and become COO-, while the amino group (NH2) will remain protonated (NH3+). So, the valine molecule will have a net charge of 0.
c. At pH 14:
At very basic pH levels, the concentration of OH- ions is high. In this case, the carboxyl group (COOH) will lose two protons and become COO2-, while the amino group (NH2) will lose its proton and become NH2-. Consequently, the valine molecule will have a net charge of -1.
To determine the charge on an amino acid at different pH levels, we need to consider the pKa values of the functional groups involved and their respective dissociation equilibria. In this case, the pKa values of valine's carboxyl group and amino group are approximately 2.2 and 9.7, respectively. By considering the pH relative to the pKa values, we can determine the charge on the amino acid.