[Schwarz107]

For once I've relied on premade flashcards to learn chemistry. I found them on Ankiweb; it's the most popular chemistry deck they have. All good so far!

But I have been using the deck for a couple of days now, and I just don't make sense of it. See the picture below.

The structure of the depicted amino acid, I don't get it to jive with what I've read about polarity today. In the dictionary, I see there are three different definitions of polar, but no matter which definition I apply, I can't see how a compound with poles should be "nonpolar".

[chenbeier]

I think the card is wrong, The molecule has positive ammonium group and a negative carboxyl anion. It is polar.

[Schwarz107]

Thanks! Appreciated!

I'll head to Wikipedia then, replacing all the images of the deck.

[Schwarz107]

Alas! This got more confusing.

I've did a Google images search for "20 amino acids", thinking I'd replace all the images in the deck with proper ones. But many of the images corroborate the story of the Anki deck. That glycine is nonpolar.

[AWK]

Each word usually has many meanings - also in science. I have seen many funny and sometimes less funny misunderstandings resulting from a different understanding of the same word, e.g. by doctors, biochemists, chemists or physicists. From the drawings presented, it is clear to me that this is an understanding of biochemists. For them, polar is that, what under physiological conditions, can attach or split a proton (during enzyme work). From these drawings, you can do it yourself because you can see multiclass classification (polar, non-polar, electrically charged with subclasses).

[Babcock_Hall]

One usually classes the side-chains of the amino acids, because all of them have the ammonium and carboxylation groups.  One classification is non-polar, polar but uncharged, cationic acid, and neutral acid.  Different authors use slightly different classification schemes.  There is a good reason for doing so.  In a polypeptide the charges on the ammonium ion and the carboxylate group are lost.  However, the polarity of the side chains is helpful in understanding the three dimensional shape of folded proteins.