Symbol: Gly G
Molecular Weight: 75.07
Isolectric point (pH) 6.06
Molecular Formula: C₂H₅NO₂

Glycine is a nonpolar amino acid. It is the simplest of the 20 natural amino acids; its side chain is a hydrogen atom. Because there is a second hydrogen atom at the α carbon, glycine is not optically active.

Since glycine has such a small side chain, it can fit into many places where no other amino acid can. For example, only glycine can be the internal amino acid of a collagen helix.

Glycine is very evolutionarily stable at certain positions of some proteins (for example, in cytochrome c, myoglobin, and hemoglobin), because mutations that change it to an amino acid with a larger side chain could break the protein's structure.

Most proteins contain only small quantities of glycine. A notable exception is collagen, which is about one-third glycine.

In 1994 a team of astronomers from the University of Illinois, led by Lewis Snyder, claimed that they had found the glycine molecules in space. It turned out that they had not. But eight years later, in 2002 Lewis Snyder and Yi-Jehng Kuan from National Taiwan Normal University repeated the finding, this time for real. The evidence that molecules of glycine exist in interstellar space was found when 10 spectrum lines of glycine were identified by radio telescope.

According to computer simulations and lab-based experiments, glycine was probably formed when ices containing simple organic molecules were exposed to ultraviolet light.

Before glycine, more than 130 simpler molecules were found in deep space, including sugars and ethanol. But amino acids, sometimes called building blocks of life, are a much more interesting find.

This does not prove that life exists outside Earth, but certainly make that possibility more likely, proving that amino acids exists in outer space. This also indirectly supports the idea of Panspermia, saying that life was brought to Earth from space.

Physiological function

Glycine is an inhibitory neurotransmitter in the central nervous system, especially in the spinal cord. When glycine receptors are activated, chloride ions enter the neuron and the cell undergoes a hyperpolarization. Thus the cell tends to be in an inhibited state. Strychnine, a drug that cause convulsions, acts by blocking these glycine receptors.