There are basically 4 classes of amino acids: Non-polar Polar Acidic Basic In terms of 3D fold - i.e. the general abstract shape of the protein in 3D, you

There are basically 4 classes of amino acids: Non-polar Polar Acidic Basic In terms of 3D fold - i.e. the general abstract shape of the protein in 3D, you can make loads of substitutions without changing it, generally as long as you stay within the same class. It's not until you compare the 3D shape that you see the relationship.