Which amino acid is optically not active

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The D and L forms of the amino acids

Most amino acids have different spatial structures in nature. They owe these properties to a chiral center (at C.αAtom), which has four different substituents. A distinction is made between a D-shape (from dextro, right), in which the amino group of the Cα Atom in the Fischer projection to the right, and an L-shape (from levo, left), in which it stands to the left. Since the molecules are the same and only differ in their spatial structure, they also have identical chemical and physical properties. With one exception: enantiomers turn the plane of oscillation of polarized light either to the left (-) or to the right (+). But be careful: You cannot deduce the rotational properties +/- from the D / L shape, since the D / L classification only relates to the arrangement of the substituents on the Cα-Atom refers!

Amino acids and carbohydrates occur as mirror image isomers, but one form is preferred in all living things. Proteins are made almost entirely from L-amino acids; long-chain polysaccharides and DNA, on the other hand, are made up of D-sugars. This correspondence in all living beings is also interpreted as an important indication of the common origin of all life.

D- and L-shapes cannot be merged - anyone who has ever put on the wrong glove will notice this. A click on the picture starts the animation.

The amino acid serine in its L-form (left) and in its D-form (right)