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#4. The R represents the side chain of the amino acids which make up the anti-parallel beta sheet. Since a wide variety of side chains can exist on a beta -sheet, they generalize the structure by writing Rs instead of specific amino acid side chains.
The side groups are what make each amino acid different from the others. Of the 20 side groups used to make proteins, there are two main groups: polar and non-polar. These names refer to the way the side groups, sometimes called R groups, interact with the environment. carboxyl group is made up of one carbon (C) and two oxygen (O) atoms. That carboxyl group has a negative charge, since it is a carboxylic acid (-COOH) that has lost its hydrogen (H) atom. What is left â the carboxyl group â is called a conjugate base. The second carbon is connected to the amino group.