"Mirror" Molecule: Carvone

Air Date: 01/21/2011
Source:
NBC Learn
Creator:
Beth Nissen
Air/Publish Date:
01/21/2011
Event Date:
01/21/2011
Resource Type:
Science Explainer
Copyright:
NBCUniversal Media, LLC.
Copyright Date:
2011
Clip Length:
00:04:15

This NBC Learn video "profiles" a chiral or mirror-image molecule, carvone, and explains how the "handedness" of a molecule can change its properties -- resulting, in carvone, in the distinctly different flavors and aromas we perceive as spearmint, caraway and dill.

"Mirror" Molecule: Carvone

BETH NISSEN, reporting:

Spearmint. Caraway. Dill. A chewing gum flavor, a seed in rye bread and an herb in pickles. Wouldn’t seem they have anything in common – but they do.

Reduce spearmint, caraway seed and dill to their essential oils and a sizable percentage of all three turn out to be made up of the same molecule: carvone.

How can you explain one molecule being responsible for distinctly different smells and tastes? With two hands, a mirror, a lightbulb and a pair of gloves.

Start with the basics: Carvone’s chemical formula tells you what it’s made of: 10 atoms of Carbon, 14 atoms of Hydrogen, and 1 atom of Oxygen.

Just as important as how many atoms of what elements make up a molecule, is how those atoms are bonded together, and in what configuration, or structure.

We think of molecules (when and if we think of molecules)… as having only one set structure: this is H2O, for example, not this, or this.

But a molecule like Carvone can have slightly different arrangements of their atoms – and still be the same molecule like a girl who has different “looks” depending on how she parts her hair, or the way she wears a sweater. As long as how she rearranges her hair and clothes doesn’t add or take away anything, she’s still the same girl in the same outfit.

The carvone molecule has two slightly different “looks” or, as they’re called, stereoisomers: this one and this one.

Stereoisomers are three-dimensional, but it’s easier to understand these two by looking at a standard two-dimensional drawing of their structures. Notice anything? The two are mirror images of each other.

Some structures, like, say, a lightbulb, are the same in mirror image or side by side. But carvone stereoisomers are like a pair of hands: A hand and its mirror reflection will exactly match, but hands aren’t the same side-by-side, or superimposed.

Actually, carvone stereoisomers are like left and right hands even down to their names:
This one is R-carvone. The R stands for the Latin word meaning right. The structure of this gives spearmint its taste and smell.

Its mirror opposite is S-carvone. The S stands for the Latin word meaning left. The way this one is arranged is what gives caraway its flavor and aroma and dill, too. In pure form, the two flavors are almost the same.

This kind of left-handed/right-handed molecule is called chiral – carvone has chirality, terms, not coincidentally, from a Greek word meaning hand.

The Greek word for nose is rhinous yes, as in rhinocerous, which is the way we’ll segue into this next part, on how your nose and tongue work to distinguish the difference between the smells and tastes of spearmint or caraway or dill…through specialized receptors that interact with molecules in very specific ways.

Think of some receptors as structured like baseball mitts, specifically designed to pick up molecules with structures like baseballs, but not footballs, which have their own receivers.

These receptors are SO highly specialized that they interact distinctively with molecules that differ only in very small ways, like their handedness. Almost as if some receptors are like right-handed gloves able to pick up only the R-carvone molecules, recognize them, and send a message to the brain saying “It’s spearmint!” And as if S-carvones only fit into left-handed glove receptors, who recognize them and tell the brain: “It’s caraway!” or “It’s dill!” There you go: a ‘handy’ explanation of carvone.

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