The polarity and acid/base character of each R group is the main factor determining the characteristics of an amino acid.
There are four types of R groups:
• nonpolar, e.g., CH₃ in alanine
• polar, e.g., CH₂OH in serine
• acidic. e.g., CH₂COOH in aspartic acid
• basic, e.g., CH₂(CH₂)₃NH₂ in lysine
The R group determines whether an amino acid is acidic, basic, or neutral.
However, the nature of the R groups is the major factor that determines the 2° and 3° structures of polypeptides and proteins.
