Final answer:
At pH 7, tyrosine is electrically neutral because the deprotonated carboxyl group and protonated amino group balance each other out. Its isoelectric point is around 5.66, below which it would carry a positive charge, and above which it would carry a negative charge, but the phenolic side chain does not deprotonate at this pH.
Step-by-step explanation:
The overall charge of tyrosine at pH 7 can be determined by considering its amino and carboxyl groups, as well as the phenolic hydroxyl group in its side chain. At pH 7, the carboxyl group (-COOH) will be deprotonated and carry a negative charge (-COO-), and the amino group (-NH3+) will be protonated carrying a positive charge. The phenolic hydroxyl group does not generally lose its proton at pH 7, thus it does not contribute to the charge. The net charge of tyrosine in a neutral pH of 7 is therefore neutral, since the negative and positive charges balance out.
Tyrosine has an isoelectric point (pI) of approximately 5.66, which means at pH values below 5.66, tyrosine would carry a net positive charge, and at pH values above it, tyrosine would have a net negative charge. However, pH 7 is above its pI, so typically, one could expect tyrosine to have a net negative charge. But because tyrosine's side chain does not deprotonate significantly until higher pH levels, it has a neutral charge at pH 7. Note that the pH at the equivalence point of titrating a weak acid with a strong base is greater than 7, indicating that the solution would be basic rather than neutral or acidic if it involved a simple titration to that equivalence point.