Question

how do you tell if an amino acid is hydrophobic or hydrophillic?

Answer 1

You look at the structure. Lots of C-H bonds indicates that the amino acid is highly hydrophobic. C-H bonds are non-polar bonds meaning both Carbon and Hydrogen share their electrons about equally. Non-polar bonds lead to hydrophobia because water is a polar molecule and polar / non-polar do not mix well. On the other hand if you see polar bonds, such as O-H or N-H, you know that the molecule has some polarity and that it is likely hydrophilic (unless their are an overwhelming amount of non-polar bonds). O-H (Hydroxl groups) are the MOST polar groups and are usually a good indicator of hydrophilia.