Overview of Stereochemistry of Amino Acids

Almost all of the vital amino acids, which are needed to form protein, are stereoisomers. That means all of them have different molecules of a compound on different sides. That is why these amino acids are known to be as chiral. Except for glycine, all the amino acids fulfil this term. 

In other words, all the amino acids have different molecules on 4 different sides. For glycine, this is different. So, all of the amino acids are chiral. That implies being a 3d structure on a plane, which can be rotated at any angle.

The mirror image of the same amino acid cannot be superimposed.

Stereoisomers

When at all 4 sides of a carbon molecule, there are 4 different compounds or molecules to create a carbon bond; this chemical phenomenon is known as stereoisomers. This property is known as the stereochemistry of amino acids. With the help of that, you can decide on an amino acid that is L-shaped or D-shaped. Along with that, these types of stereoisomers are known as chiral.

Chiral property of amino acids

Except for glycine, all of the vital amino acids have chiral properties. When an amino acid has 4 different molecules on all 4 sides, it will be able to form a 3-d image. It will also be able to rotate at any angle. So, as it’s a 3-d image, it will have a perfect mirror image.

If the amino acid is L-shaped or D-shaped, it will not be able to superimpose with their respective mirror image. Therefore, the amino acid will not match its respective mirror image from any angle. So, they will stay just as stereoisomers according to the stereochemistry of amino acids.

D-shaped and L-shaped amino acids

When the amino group (-NH2) stays on the left side of the amino acid, then it looks like an L-shaped amino acid. This can be thought of as the left hand. On the other side, D- shaped amino acids are just mirrored images of L-shaped amino acids. So d-shaped amino acids are like the right hand. But both of them can not be superimposed. Also, people believe that only D-shaped amino acids don’t even exist in the natural world. 

There comes one more type, which is known as DL-shaped amino acids. This type of acid has both D-shaped and L-shaped amino acids together by forming a chain with a bond.

Bonds of amino acids

Amino acids form bonds to make a chain, known as peptide bond formation. On amino acids, there are two sides, one is the amino side, and the other is the carboxylic acid side. The amino side of an amino acid reacts to the carboxylic acid side of another amino acid to form peptide bonds. This is how amino acid forms a peptide bond.

Peptide chains are of different types; there are oligopeptides, like dipeptides, tripeptides, tetrapeptides, etc. This can have up to 20 amino acids. Then, one more peptide is due to peptide linkage, known as a polypeptide. This can have up to 49 amino acids. When the chain of amino acids reaches 50, it becomes a protein.

Exception

There is one exception in the Stereochemistry of amino acids, glycine. Glycine has a hydrogen atom at all 4 hands of the carbon atom to form an amino acid. So, this doesn’t have a stereoisomer, or it’s not chiral, as this will not be able to form a 3-d image. But, glycine will be able to have a superimpose property with the mirror image.

Limitation

Though scientists take a count on D-shaped amino acids to have some properties, this doesn’t even have strong proof to be in the natural world. For example, there is no amino acid that will look like L-shaped amino acid in mirror images. That is why it is not a practical experiment possible with a real D-shaped amino acid to try to make any superimposition of mirror images.

Conclusion

With the help of the stereochemistry of amino acids, you will know that all the vital amino acids have stereoisomers and a chiral property. The only exception is glycine. As those amino acids are chiral, they will have a 3-d image. But none of them will be able to have a superimposition with their respective mirror images at any angle.

Also, with this property’s help, amino acids react with other amino acids to create a peptide bond and peptides. When the peptide chains become at least 50 amino acids long, it becomes protein.