Why is chirality important in living things?
1 Answer
Because if chirality is involved in biological activity then use of a racemic mixture can be dangerous. A tragic example of that is the event that occurred with pregnant women in 1960 with thalidomide.
Chirality effects were to blame for the deformity of their offsprings.
Explanation:
Optical isomers can influence the structure of biological molecules e.g. L-amino acids joined in a polypeptide chain form a RH (right-handed) alpha-helix whereas D-amino acids form a LH alpha-helix. Found that RH alpha-helix is more stable than LH alpha-helix, and even single amino acids L-alanine is very slightly more stable than D-alanine.
Difference between L & D isomers is in the nuclear interactions between protons, neutrons & electrons. These cause optical activity, and are responsible for weaker interactions in D-amino acids. With increasing exposure of human populations to a wide range of chemicals such as drugs, food additives, flavour substances, agricultural chemicals etc., there is a need to be aware of chirality requirements and different effects of different isomers.
Need to be aware that two optical isomers are almost identical, and if only one is used in the body then presence of the other isomer can act as a competitive inhibitor (bad thing). Only L-amino acids used in protein synthesis, and presence of D-amino acids leads to faulty proteins.
If the chirality property has no effect on the function of the molecule then it should be safe to use racemic mixture. If chirality is involved in biological activity then use of a racemic mixture can be dangerous.
A particularly tragic example attributed to chirality occurred in early 1960's when a synthetic tranquilizer thalidomide was widely prescribed as a sedative. It was used by some pregnant women who later gave birth to deformed children.
The drug was administered as a racemic mixture. Later it was found that one isomer was teratogenic and interfered with DNA metabolism, while the other isomer was safe. The L-isomer produced the teratogenic effect, which resulted in the severe foetal abnormalities.
