<Tr> <Td> Aliphatic (non-aromatic) </Td> <Td> </Td> <Td> Ψ </Td> <Td> V, I, L, M </Td> </Tr> <Tr> <Td> Small </Td> <Td> </Td> <Td> π </Td> <Td> P, G, A, S </Td> </Tr> <Tr> <Td> Hydrophilic </Td> <Td> </Td> <Td> ζ </Td> <Td> S, T, H, N, Q, E, D, K, R </Td> </Tr> <Tr> <Td> Positively charged </Td> <Td> </Td> <Td> + </Td> <Td> K, R, H </Td> </Tr>

Where does variation exist in the general structure of the amino acid