Final answer:
Positively charged R groups are found in the side chains of basic amino acids, namely arginine, lysine, and histidine, and they contribute to the structure and function of proteins.
Step-by-step explanation:
Three examples of positively charged R groups, which are the side chains of amino acids in proteins, include the R groups found in the basic amino acids arginine (Arg), lysine (Lys), and histidine (His). These R groups carry a positive charge because of their ability to accept protons. Their positive charge plays a critical role in the complex three-dimensional tertiary structure of a protein by contributing to ionic bonds and influencing how the protein folds. The chemical nature of the R groups such as those in lysine and arginine being positively charged makes them basic amino acids. These R groups can foster interactions that are essential for the structure and function of proteins.