91Ó°ÊÓ

• Proteins are made up of amino acids that have an acidic carboxylic acid group, a basic amino group, and a variable substituent called R.

• Because the carboxyl group is more acidic than the ammonium group, the nonionized form spontaneously rearranges to the zwitterion, which has both positive and negative sites

In this problem we will determine which four amino acids from Table 10-1 have acidic substituents and which three have basic substituents.

Acidic substituents

Acidic substituents that donate a proton are given below:

• aspartic acid

• cysteine

• glutamic acia

• tyrosine

Basic Substituents

Basic substituents that accept a proton are given below:

• arginine

• histidine

• tysine

Therefore the acidic and basic substituents are found.