The Problem of Homochirality

Can life arise spontaneously from non-living chemicals? Scientists have spent many hours and vast amounts of research money attempting to prove it can. One of the many challenges they must solve is the problem of homochirality.

All the large molecules required to make a living cell are composed of building blocks that have mirror images. When you look in a mirror, you see a reversed image of yourself. The right hand appears to be on the left and vice versa. The right- and left-hand analogy is used when referring to the building blocks of life. Those building blocks come in either right or left-handed forms. We call that handedness “chirality” from the Greek word for hand. Homochirality means having the same handedness.

Life almost exclusively uses only one chirality. The amino acids that make up proteins are left-handed. Scientists are uncertain why, but they have to accept the fact that to build the proteins that RNA and DNA molecules require for life, you must have only left-handed amino acids.

In nature, amino acids are not homochiral. They come in a distribution of about 50/50 left and right, creating the problem of homochirality. For amino acids to form the building blocks of life, they would have to be homochiral. Scientists have yet to find a way to make that happen, even in the laboratory. They aren’t even sure why life requires it since the chemical properties of mirror-imaged compounds are the same for all practical purposes.

The problem of homochirality is one of the many obstacles that prevent non-living chemicals from coming together to form life without intervention by an intelligent force. Even the intelligence of our best scientists has not overcome those obstacles. I saved an Associated Press news release from 2007 titled, “Scientists Believe Artificial Life Will Be Possible in 3 to 10 Years.” We are well past that goal, and I suspect they are not much closer today. 

— Roland Earnst © 2023