Based on the pKa of the histidine side chain given in the passage, which of the following best describes the charges of the His-His dipeptide side chains at pH 7?A.The side chains all have a charge of 0.B.The side chains all have a charge of +1.C.Most of the side chains have a charge of 0, but a small percentage have a positive charge.D.Most of the side chains have a charge of +1, but a small percentage are neutral.

To answer this question, we need to understand the concept of pKa and how it relates to the charge of a molecule. The pKa of a molecule is the pH at which half of the molecules are deprotonated (carry a negative charge) and half are protonated (carry a positive charge).

If the pH is lower than the pKa, the molecule will carry a positive charge because the environment is acidic and the molecule will accept a proton. If the pH is higher than the pKa, the molecule will carry a negative charge because the environment is basic and the molecule will donate a proton.

In the case of the histidine side chain, if the pKa is not given in the passage, we cannot determine the exact charge. However, the pKa of histidine is typically around 6.0.

At pH 7, which is higher than the pKa of histidine, most of the histidine side chains would be deprotonated and carry a charge of 0. However, because the pH is close to the pKa, there would still be a small percentage of histidine side chains that are protonated and carry a positive charge.

Therefore, the best answer would be C. Most of the side chains have a charge of 0, but a small percentage have a positive charge.