Matter brought to Earth by meteorites, could become models for the building blocks of life, the researchers reported. This hypothesis is able to explain why DNA molecule always twisted in the same direction. Simulate the effects of an ancient meteorite that fell in the primordial soup on Earth, Sandra Pitstsarello chemist from the University of Arizona and her colleagues have shown how the chemistry of life could acquire a tendency to twist in the same direction.
Many organic molecules have two forms — a mirror of each other. Typically, in chemical reactions produced an equal amount of both. But biological compounds exist predominantly in one form or another. For example, DNA is wound clockwise. This is because the backbone of the DNA double helix is composed exclusively of dextrorotary deoxyribose sugar molecules. In contrast, all the amino acids are twisted anticlockwise. However, no one knows where do these preferences.
One way to get twisted to one side of the molecule — is the use of sample molecules. Therefore, the group began searching Pitstsarello sample, which could be present when life arose on Earth. They stopped at isovaline — an amino acid found in the Murchison meteorite that fell to the Australian city of Murchison in 1969. This stone more than 4.5 billion years — that is, it is about the same age as Earth.
This meteorite contains about one-third more left-twisted isovaline than dextrorotary, as well as other amino acids with the same feature. Perhaps the amino acids were formed from a mixture of simple molecules on an asteroid, which broke away from the stone. Polarized light some of the neutron star could selectively destroy more dextrorotary molecules, leaving an excess of left-twisted forms.
Pitstsarello mixed isovaline (both forms in the same proportions as in the meteorite) with two carbon compounds, which are considered to have been distributed on the Earth — glyukoaldegidom and formaldehyde. In the course of the reaction turned threose — a simple sugar commonly in living beings. And dextrorotary threose was a 5% increase. According to the researcher, this is enough to start the asymmetry in the distribution of sugar. Interesting point: isovaline helps molecules to fold into a spiral.
Threose not present in DNA. But it forms the backbone of the molecule similar to multinationals. Some experts believe that life would be easier to start with the TNC as threose easier than deoxyribose, which lies at the base of the DNA. As the TNC can also fold into a double helix, it is possible that at some stage have been replaced by another one sugar.
Battery News, 24.02.2004 17:38