Evolution On Trial

Spiritual Health Learning Community Center Exploring Life's Horizons

» Evolution Menu

Beach Front Property On A Warm Little Pond - Part Four

| Part 1 | Part 2 | Part 3 | Next | Part 6 |

| Table of Contents For Evolution On Trial |

Dr. Yardley, in the context of the present discussion, what relevance would the process known as a 'Strecker synthesis' have?" asked Mr. Mayfield.

"In synthetic, organic chemistry," responded the professor, "a Strecker synthesis generally involves bringing about the hydrolysis of, say, an amino nitrile in the presence of a strong acid. An amino nitrile joins together some kind of amino group or radical with a cyanogen or compound containing the group CN.

"Many researchers have accepted the pH value of the early, prebiotic ocean to be around 8, plus or minus 1. This means that the ancient ocean was considered to be either slightly basic, if it had a pH of 8-9, or relatively neutral, if its pH was around 7.

"Under such conditions, Strecker synthesis, which usually is done in the presence of a strong acid, would require a long time to hydrolyze organic compounds in the early, prebiotic ocean. Some researchers have set this figure at around 10,000 years.

"However, relative to tens and hundreds of millions of years, 10,000 years is really just a drop in the ocean, so to speak. This kind of synthesis would have had the opportunity to run to completion many times over during the course of the Archean era.

"I should note, Mr. Mayfield, that although the Strecker synthesis process is considered by evolutionary theorists to be an adequate means of producing amino acids in the ancient oceans, some sort of additional mechanism of concentration and condensation would be required to produce, say, the purine, nucleic base, adenine. This is where processes such as evaporation, freezing and dehydration, along with hot, anhydrous conditions, which are believed to have been present in certain intertidal zones, would play important roles in chemical evolution on early earth."

"At this point, Dr. Yardley," requested the lawyer, "would you say a little about current thinking in relation to the nature and possible origins of membranes? I believe such a discussion will bring us a little closer to providing the jurors with a proper, introductory overview of evolutionary theory, by means of which they will be able to reach an informed judgement on the matter before the court."

"I suppose," Professor Yardley mused, "that molecules known as amphiphiles are as good as place as any with which to begin talking about the origins of membranes. Amphiphiles have sort of an aura of split-personality about them.

"One part of this kind of molecule has hydrophilic properties and, as a result, is inclined to enter into interactions with water. The other part of the molecule entails hydrophobic characteristics and, therefore, tends to avoid, whenever possible, interacting with water.

"When amphiphiles are immersed in an aqueous environment, the hydrophobic aspects of the molecule curl up into small spheres known as vesicles. These tiny spheres form a protected space within which, given the right conditions and chemical reactants, various chemical processes could take place.

"The hydrophilic portion of amphiphiles, that is, the parts of the molecule which have an affinity for water, surround the hydrophobic aspects of the molecule. Not only do these hydrophilic portions represent an additional layer of separation between water and the interior, hydrophobic aspects of the amphiphile molecule, the water-loving components of the molecule also are free to enter into reactions with water.

"As such, amphiphile molecules possess some of the basic features of biological membranes. More specifically, the membranes of living organisms tend to be bilayered or have two membranes that are separated from one another by a relatively short distance, and the whole bilayered structure surrounds the interior of the cell.

"To be sure, the layered arrangement in amphiphile molecules is not quite the same as the sandwich structure of biological membranes. Most notably, there is no separate, distinct region between the hydrophilic and hydrophobic components of the amphiphile molecule, as there is in true, biological membranes.

"Nonetheless, in both true membranes as well as amphiphile molecules, one does have a double- layered arrangement surrounding an interior space or spaces within which chemical reactions could take place. Furthermore, both true membranes as well as amphiphile molecules, consist of hydrophilic and hydrophobic aspects.

"Consequently, amphiphile molecules could be considered to constitute a rather crude facsimile, or early precursor, of later, more complexly evolved, biological membranes. Interestingly enough, in this respect, some researchers maintain that exogenous organic materials - that is, organic materials from sources such as meteorites and interplanetary dust particles, may be quite rich, perhaps even preferentially so, in amphiphilic vesicles or spheres.

"Lipids, which are one of the main components in biological membranes, come in different varieties. As far as biological membranes are concerned, some of the more important lipids are composed of, among other things, a hydrophobic hydrocarbon component linked to a hydrophilic phosphate group, together with certain alcohols and/or bases.

"Lipids do not form polymers or chains of monomer units as, say, amino acids and nucleic acids do. This is because lipids are stabilized by non-polar physical forces instead of the covalent chemical bonding that characterizes polymerized compounds.

"These non-polar physical forces are essentially thermodynamic in nature. Non-polar hydrocarbons, such as oil, do not enter into solution when placed in water- water being a polar molecule.

"Hydrocarbons have a tendency to disrupt, at least in part, the array of hydrogen bonding present in water. The most stable thermodynamic arrangement - that is, the arrangement in which all of the molecules of a system have achieved their lowest chemical potential for reactivity, is one in which hydrocarbon molecules aggregate into a separate phase form, such as droplets, away from water molecules.

"This process of phase separation between non-polar hydrocarbon molecules and polar water molecules is known as the hydrophobic effect. This effect serves as a significant force helping to stabilize various kinds of macro molecular systems, including membranes, in biological organisms.

"The hydrophobic effect does not involve any chemical transformations. It only reflects the natural preference, or self-organizational drive, of molecules to arrange themselves in ways that distribute the energy of the molecular system in the least chemically reactive, and, therefore, most stable state.

"Some evolutionary scientists have suggested that the hydrophobic, hydrocarbon portion of lipids might have been synthesized or formed by a Fischer-Tropsch-like reaction. This process starts with carbon monoxide and hydrogen which are placed under pressure, ranging from one to fifty atmospheres, as well as heated to temperatures that may vary from 180 to 300 degrees Centigrade.

"Usually, this reaction is done in conjunction with a catalyst of some sort. Many catalytic possibilities exist, but, quite frequently, the ones that are used are either nickel or iron supported by a layer of silica.

"Phospholipids, which are one of the fundamental building blocks of biological membranes, come in several forms. They are polar molecules in which the phosphate group has a negative charge, the alcohol group has a positive charge, and the complex hydrocarbon tail is hydrophobic in nature.

"More importantly, phospholipids, once formed, have been observed to assemble, spontaneously, into stable lipid bilayers and vesicles within an environment of water because of the aforementioned thermodynamic forces which are at work. The hydrophilic components of the molecule form the portions of the bilayer that will be in close proximity to water molecules, whereas the hydrophobic portions of the molecule form the aspects of the bilayer which will be phase separated from water molecules.

"Some scientists have approached the issue of the first, primitive cellular prototype from a different direction than that of amphiphilic molecules composed of both hydrophobic and hydrophilic components. These researchers have focused on certain kinds of protenoid micro spheres which have been observed to form under certain experimental conditions.

"Once again, this sort of proto cell structure would form a phase separation between the outer, aqueous environment and the inner regions of the micro sphere formed by the protenoids. These inner regions could serve as a location for various kinds of chemical reaction to take place under conditions which are, to some extent, protected and stable.

"All membranes of living organisms consist of a combination of phospholipids and proteins. Therefore, if one were to combine the idea of protenoid micro spheres and amphiphilic molecules, one would be getting quite close, in some respects, to the structural character of modern biological membranes.

"A cell is really a micro-environment bounded by a membrane. The phospholipid portion of the membrane constitutes a permeability barrier which helps stabilize and protect the micro-environment of the cell's interior.

"However, the down side of a permeability barrier is that it can keep out various kinds of molecules which may be necessary to chemical reactions going on in the interior regions of the bounded micro-environment. In biological cells, this problem is solved by a variety of proteins, referred to as transmembrane proteins, which extend from one membrane layer to the other membrane layer of the bilayered structure.

"These transmembrane proteins may serve different functions. Some of them provide channel ways, linking the external aqueous world with the internal bounded micro-environment.

"Some of these membrane proteins may function as carriers, or active transports, for certain kinds of molecules. Still other forms of these membrane proteins may form part of an ion pump system which brings various ions into the cell or gets rid of such ions depending on circumstances and needs.

"When, as evolutionary biologists believe to be the case, protenoids, at some point, became incorporated into self-assembling, phospholipid membrane structures, a major step would have been taken toward the first proto cell. Various experiments of nature may have ensued then, exploring different arrangements and kinds of protenoids in the membrane, some of which were naturally selected because of their ability to serve, in some minimum fashion, as channels, or carriers or parts of an ion pump system.

"Researchers feel those protenoids would have been favored which had particular kinds of primary structure. More specifically, the sequence of amino acids constituting the primary structure of the protein should be such that, under the influence of purely thermodynamic, self-organizing forces, the tertiary folding pattern brought about by these thermodynamic forces would need to have arranged hydrophilic and hydrophobic aspects of the protenoid in a certain manner.

"On the one hand, hydrophilic portions of the transmembrane protenoid would need to be at the opposite ends of the membrane where they would be exposed to water molecules surrounding the cell as well as within the cell. On the other hand, those portions of the protenoid structure which were hydrophobic should be folded away in the region between the two bilayers - a region which consists of hydrophobic lipid molecules.

"Prior to the appearance of such phospholipid-protenoid micro spheres, there may have been transitional structures. Liposomes, for example, are small vesicles composed of fluid, lipid bilayers.

"Liposomes have the capacity for reversible breakage. In other words, under various conditions, they can break open and, then, spontaneously reseal.

"Thus, when liposome vesicles are agitated in an aqueous environment, they will break open at various points and, afterward, reseal. This process of breaking and resealing enables the liposome to capture any solutes which may happen to be in the environment.

"Similarly, when liposomes are dried, they often form multi-layered structures. Solutes can become trapped within these structures. When the dried liposome becomes rehydrated, the trapped solutes become sealed within the micro-environment of the liposome's interior.

"The property of being able to break and reseal could serve another function beyond providing a mechanism for admitting different kinds of solute materials into the liposome's interior region. Growth, division and multiplication, of a sort, also could be associated with this capacity to break and reseal.

"If one were to add some of the potential properties of a liposome to those of phospholipids and protenoids, then the possibilities become even more intriguing. Such an amalgamation of properties is coming much closer to what we would recognize as a cell-like structure or proto cell."

| Part 1 | Part 2 | Part 3 | Next | Part 6 |

| Table of Contents For Evolution On Trial |