​IMPORTANT: The little white part is the interchangeable "R group"​. This little "group", if changed, can change the properties of the amino acid.

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If the properties are changed, it affects how the amino acids in a polypeptide chain will interact, and therefore, how a protein will fold. Shape = function, so this is a BIG DEAL.

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Make sense?

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Great! Now, how to tell if an amino acid will be "POLAR" or "NONPOLAR" by its "R group":

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Remember "POLAR" has "poles" or ends with opposite charge, like the North vs the South Pole--or negative charge vs positive charge. POLAR stuff is attracted/attractive to other POLAR stuff.

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POLAR "R groups" will be ionic-y, magnet-y, and bind-y to other POLAR amino acids, and will bend to bind to them.

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If the "R group", at the tip, has hydroxyl (-OH), sulfhydryl (-SH), ​ or oxygen (it's very electronegative!)--that amino acid will act POLAR-y. Not only will it bend toward other polar amino acids, but to water as well.

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​NONPOLAR means it has no opposite poles of charge, so NONPOLAR stuff stays to itself. Fatty stuff is NONPOLAR, and C-H bonds (since Carbon and Hydrogen have similar electronegativity) are also NONPOLAR. (The C-H bonds are the easiest tell. Remember that organic symbols are made of C-H bonds: (tricky how they can write the symbols, huh?)

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So: if the "R group" has C-H bonds at the tip, that amino acid will act NONPOLAR-y. It will bend away from water and will tend to move toward other NONPOLAR amino acids. (They like other nonpolar stuff only.​) See the trend? POLAR only likes other POLAR stuff, and NONPOLAR only likes other NONPOLAR STUFF--this is the reason why acetone works to take off Sharpie marks, but water doesn't.)

​NONPOLAR  

Ready to try?

Is this amino acid Polar or Nonpolar?​ (There are 20)