One of two molecules for this week
October 29, 2018
Please don’t be afraid of us this week.
What molecules are we?
Image of L-Alanine

L-Alanine1 and L-serine1 are amino acids that are necessary for the biosynthesis of proteins. They are considered “nonessential” in human diets (and those of most other animals) because they are synthesized in the body.

In 1850, long before it was discovered in and isolated from natural substances, alanine was synthesized from acetaldehyde by German chemist Adolph Strecker. Of course, Strecker made the D,L-racemate of the amino acid rather than either isomer alone.

Serine, on the other hand, was first discovered in nature, specifically in silk protein, by German chemist Emil Cramer in 1865. And, speaking of silk . . .

Alanine and serine, along with previous Molecules of the Week glycine and L-proline, are the major amino acids in spider silk proteins. Alanine-rich crystalline areas give silk strength, whereas glycine-rich amorphous regions provide elasticity.

Halloween reminds us of spiders. Spiders spin webs of silk. Silk is made up of proteins. Proteins are polymers of amino acids. Who would have thought that such simple molecules could be scary?

1All amino acids that are biosynthesized into proteins are the L-enantiomers. Some D-enantiomers appear in nature, but they are relatively rare.

L-Alanine hazard information

GHS classification*: not a hazardous substance or mixture 

*Globally Harmonized System of Classification and Labeling of Chemicals. Explanation of pictograms.

L-Serine hazard information

GHS classification: not a hazardous substance or mixture 

MOTW update: October 29, 2018

Skatole was the Molecule of the Week for March 5, 2012. It’s what causes mammalian feces to smell bad. Recently, scientists in China, Singapore, and the United States reported the discovery of the enzyme, indoleacetate decarboxylase, which bacteria use to convert tryptophan to skatole in the gut.


L-Alanine fast facts

CAS Reg. No.56-41-7
Empirical formulaC3H7NO2
Molar mass89.09 g/mol
AppearanceWhite crystals or powder
Melting point≈300 ºC (dec.)
Water solubility167 g/L

L-Serine fast facts

CAS Reg. No.56-45-1
Empirical formulaC3H7NO3
Molar mass105.09 g/mol
AppearanceWhite crystals or powder
Melting point220–250 ºC (dec.)
Water solubility425 g/L

MOTW update: November 5, 2018

L-Alanine and L-Serine were the Molecules of the Week for October 29, 2018. They, along with glycine and L-proline, are the chief amino acids that make up spider silk proteins. In the past month, chemists at San Diego State University and Northwestern University (Evanston, IL) discovered that before spiders spin their silk, they store the silk proteins in complex nanoparticles.

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Learn more about this molecule from CAS, the most authoritative and comprehensive source for chemical information.

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