Thursday, December 15, 2016
Formation of Organic Molecules, the Haldane-Oparin Hypothesis
The early chemical steps toward life have a good theoretical basis. The basis is found in a 1920’s hypothesis credited to a Russian biochemist, Alexander Oparin, and an English biologist, J. B. S. Haldane. Each hypothesized the first formed atmosphere lacked oxygen, but contained ammonia, and had reducing properties. The chemicals of the atmosphere interacted in the presence of ultra-violet light, lightening, and volcanic heat to produce the chemical precursors of living systems. Biologists think the precursors accumulated in the water and somehow assembled into primitive living systems. Such steps were necessary because free oxygen is produced by photosynthesis and would not have existed in abundance prior to photosynthetic organisms.
The ammonia was formed as it can be today from the effect of lightening upon atmospheric nitrogen and water vapor. Carbon dioxide was abundant in the early atmosphere.
An experiment in 1953 by Stanley Miller and Harold Urey in Chicago . . . . . .used sparks in the atmospheric portions of the system to simulate lightening. They cooled a portion to condense water along with products in solution that were present or produced. Analysis of the condensate showed some amino acids and other organic compounds, most of which are components of living systems.
Concentration of Organic Molecules
The most important mechanism may have been concentration by evaporation of water. Low tide could have made it a daily event in intertidal areas. But higher splash zones may have had longer periods of isolating pockets of water for greater concentration.
A second mechanism is by coacervate production. The coacervates are small globules of organic material that accumulate other organic molecules because their solubility in each other is greater than their solubility in water. This . . . . . .could have been the route of biological membrane formation. Membranes . . . form naturally in systems where an abundance of the proper lipid molecules are present. The water insoluble ends are semi-dissolved in each other and repel the water soluble ends so a double layered membrane forms automatically. The third mechanism, adherence to particulate items may have been especially prominent in pockets of water along the shore. It might be thought of as the “bathtub ring” origin of life. It is perhaps the least certain of mechanisms, but seems a possible explanation for aiding the origin of some of the biochemical processes where minerals are important components.
[The preceding is adapted from pp. 74 and 75 of my 2009 Evolution Insights unpublished manuscript.]
Alternative Views of Organic Molecule Formation
An alternative view of the origin of life was proposed by a marine biologist, Corliss, who, noting the abundance of life at deep sea vent locations where the animals surround volcanic heat and emissions produced chimneys, suggested such sites were where it all started. An earlier experimental observation by a scientist at a newly formed island near Iceland showed that lava and seawater interact to produce a few amino acids and small organic molecules. In the early history of the earth lava/seawater interactions were presumably more widespread and included many more shallow water locations. Such locations undoubtedly contributed to the organic content of the original oceans but are unlikely to have been the location where animals originated for two reasons. One, they come and go with change in lava production and are limited in geographic extent to mostly where crustal plates meet. Two, the fossil record indicates older forms of life seem to have originated in shallow coastal areas and progressively over time show representatives in deeper waters.
Few accept biblical accounts of creation of life details. Certainly, God could have created the world and its inhabitants, fossils and all, in a short time, but doing it in the billions of years and with the details supporting the amazing story of evolution seems like an even grander way and leaves people with the kind option of not demanding immediate belief in an infinite deity that is all loving, kind, and merciful.
Evolutionary Consequences of the Haldane/Oparin Hypothesis
1. The first compounds formed, including such amino acids as glycine and adenine, became important building blocks for living systems. Adenosine triphosphate, the energy currency of the cell, and the unique structure of DNA with adenine as the basis for one of its four nucleotides of the genetic code, were important consequences.
2. Functional values of early steps were retained as basic, but slightly modified, characteristics seen in descendant organisms. The gradual changes leave helpful clues for tracing the evolutionary history of animals as well as plants.
3. Photosynthesis, upon which we are so dependent today, makes shallow seas and coastal regions the most likely place of life's origin.
4. DNA’s early origin before the oxygen laden atmosphere developed meant the development of the nuclear membrane probably developed after photosynthetic bacteria. The nuclear membrane enables DNA to operate in the part of the cell where it experiences the cell's lowest oxygen content area most like it experienced in its early origin.
5. Billions of stars have planets where now or in the past similar conditions led to production of the same basic building blocks. Such beyond earth production makes it quite possible that fragments of extraterrestrial bodies containing such organic compounds may have impacted earth without proving life was present on the source planet. Planets in other galaxies, as well as in the Milky Way, have undoubtedly had similar periods with similar conditions to earth with somewhat similar evolutionary histories of life.
Joseph G. Engemann, Emeritus Professor of Biology, Western Michigan University, Kalamazoo December 15, 2016