It may be a right-handed world, but recent Purdue University research indicates that the first building blocks of life were lefties – and suggests why, on a molecular level, all living things remain southpaws to this day.
This schematic illustrates Cooks theory of how serine, one of the 20 amino acids that comprise all living things, may have determined the chirality of other biological molecules at the dawn of evolution. "Left-handed" serine, shown here as L-serine, has virtually the same properties as "right-handed" D-serine. But because of an unknown process that possibly caused L-serine to become more prevalent than D-serine in the environment, the strong clusters that L-serine forms bonded only with other left-handed amino acids and right-handed sugars. Other biological molecules with an incompatible chirality were left out of the bonding process, and all the organisms on the planet eventually developed from amino acids with exclusively left-handed chirality.
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In findings that may shed light on the earliest days of evolutionary history, R. Graham Cooks and a team of Purdue chemists have reported experiments that suggest why all 20 of the amino acids that comprise living things exhibit "left-handed chirality," which refers to the direction these basic biological molecules twist–and how a single amino acid might be the reason.
Amino acids can be oriented either to the left or the right and possess the same chemical properties regardless of their chirality. But somewhere along the line, living things evolved using only amino acids of the left-handed variety. Scientists have puzzled over the reason for many years, but Cooks’ group seems to have found the answer: A single amino acid called serine set the standard eons ago, forcing all other biological molecules to follow suit.
Chad Boutin | Purdue University
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