"Dr. Yardley," stated Mr. Tappin, "you have testified that ribose, is a 5-carbon monosaccharide, or pentose sugar monomer. In addition, you said this sugar, along with phosphates and nucleic bases, are fundamental building blocks of nucleic acids, and nucleic acids are the carriers of genetic information.

"How do evolutionary theorists account for the synthesis of ribose sugars in the prebiotic Archean era?" asked the defense counsel."

"Many researchers feel," the professor replied, "that a process known as the formose reaction may have been the most plausible means of synthesizing a variety of sugars, including ribose. Essentially, this involves a base-catalyzed condensation reaction of formaldehyde."

"Leaving aside for the moment," said the lawyer, "the previously established point concerning the possible, relative unavailability of formaldehyde in a prebiotic environment due to, among other things, ultraviolet photolysis, would you describe, in a little more detail, the nature of the formose reaction."

"If," began the professor, "one takes a strong alkali agent such as thallium hydroxide or lead hydroxide and treats formaldehyde with one or the other of these agents, one can generate a variety of sugars. On the other hand, one also can use agents like alumina - that is, aluminum oxide (Al₂O₂), as well as calcium carbonate or barium hydroxide.

"Following an induction period - that may last for many hours and in which products such as glycolaldehyde, glyceraldehyde and dihydroxyacetone are formed, a variety of sugars are synthesized. These include tetroses, pentoses and hexoses, or, respectively, 4-, 5-, and 6-carbon sugars.

"The formose reaction is autocatalytic in nature which means that once the induction period is over, the reaction proceeds to completion rather quickly. In addition, if the reaction is stopped at the appropriate stage, yields of up to 50% of some of the higher sugars are possible."

"Dr. Yardley, since, presumably, there was no one around in prebiotic times to stop the formose reaction at the appropriate stage, can one reasonably assume that the yields would have been considerably less than the 50 percent figure you have cited?" Mr. Tappin inquired.

"Yes, I guess so," indicated the professor. "On the other hand, there could have been forces active in the prebiotic environment that may have disrupted the reaction before it went to completion."

"I won't pursue this Archean era version of a mugging by unknown assailants," the defense counsel remarked, "but I would like to pursue the issue of the alkali agents which may be used in the formose reaction. How common would, respectively, thallium, lead, and barium hydroxide have been during the Archean era?"

"This is relatively difficult to say," the professor responded. "Perhaps the most accurate thing I can say is these hydroxides probably would have been far less plentiful than either aluminum oxide, which is very common in the silicates which make up a large portion of the Earth's crust, or calcium carbonate - that is, limestone, which also would have been quite plentiful in the prebiotic period."

"Is there," Mr. Tappin asked, "only one kind of pentose sugar - namely, ribose, which is synthesized during the formose reaction?"

"No," replied the professor. There are a number of pentoses that are formed during this reaction, and each of these pentose sugars are produced in varying amounts.

"For example, in addition to ribose, one also will find xylose, lyxose, and arabinose. These other pentoses involve various kinds of inversion of one or more of the hydroxyl groups of ribose."

"What proportion of all the different kinds of tetrose, pentose, and hexose sugars formed during the formose reaction," queried the defense counsel, "is the ribose variety of sugar?"

"Ribose forms a very small portion of the overall yield of sugars," the professor stated.

"Do the other pentose sugars beside ribose get synthesized in amounts that are comparable to, if not more than, the ribose yields?" inquired the lawyer.

"Yes, they do," answered the professor.

"What sort of concentration levels of formaldehyde are minimally necessary for the formose reaction to proceed?" Mr. Tappin wondered.

"As far as we know," the professor stipulated, "the formose reaction does not seem to proceed if the solute level of formaldehyde falls much below one-hundredth of a mole per liter of solution."

"Given," postulated the lawyer, "what has been said before about the possible scarcity of formaldehyde in the Archean era- and, perhaps, even in the best of circumstances, aren't expectations for the existence of such high solute concentrations of formaldehyde during prebiotic times rather inflated and optimistic?"

"Yes, realization of these levels of formaldehyde concentration during the Archean era could be a significant obstacle to the formation of ribose," confirmed the professor."

"Dr. Yardley, how stable are sugars in aqueous solution?"

"Not very," the professor replied, "especially if the pH value is above 7. Under these circumstances, sugars tend to be degraded over a period of time that is not much longer than what is required to synthesize such molecules."

"Previously, Professor, you stated that evolutionary researchers generally consider the pH of the Archean era ocean to have been 8, plus or minus one. Consequently, would you agree, Dr. Yardley, the pH of the Archean era ocean had a very good chance of exceeding a pH of 7 and, therefore, readily could have led to the destruction of whatever small amounts of ribose were synthesized almost as quickly as these molecules were formed."

"Yes, there could have been a very good chance this happened if the pH of the Archean era ocean was much above 7," affirmed the professor."

"Other than the issue of isomers with different-handed optical activity, does ribose come in more than one form?" the defense counsel inquired.

"Yes, it does," the professor replied. "There are three forms in all.

"In addition to a form known as ribopyranose," he explained, "there are two ringed forms of ribose. These are referred to as alpha- and beta-ribofuranose."

"Do all three of these forms of ribose appear in the nucleic acids that occur in living organisms?" asked Mr. Tappin.

"No," stated the professor. "The only form of ribose which occurs in living organisms is beta-ribofuranose."

"Nucleosides," stated the lawyer, "are one step removed from a full-fledged nucleic acid due to the absence of a phosphate group, and nucleosides consist of bonding together one of the five nucleic bases with a beta-ribofuranose. Have I got this right?"

"Yes," the professor indicated.

"Could other sugars, such as some of the non-ribose pentoses, bond with the five nucleic bases?" inquired the defense counsel.

"Yes," Dr. Yardley confirmed.

"Presumably," surmised the lawyer, "all three forms of ribose also could form bonds with the nucleic bases. Is this correct?"

"Yes, that is right," said the professor.

"Consequently," Mr. Tappin concluded, "any one of a number of pentose sugars, or different forms of ribose, or optical isomers could bond with the nucleic bases and form one species or another of a nucleoside. Yet, only one of the nucleosides, amongst this mixture of possible nucleosides, has any functional value in living organisms. Would you agree this is the case, Professor?"

"I would," Dr. Yardley acknowledged.

"How," the lawyer queried, "did the one nucleoside which would come to have functional value once living organisms arose, come to be selected from the multiplicity of very similar choices available in the Archean era environment?"

"We are not sure," Dr. Yardley admitted. "Obviously, whatever the mechanism of selection, the beta-ribofuranose nucleoside had selective value."

"What exactly do you mean, Professor, by the notion of selective value?" asked the defense counsel.

"The beta-ribofuranose nucleoside worked," the professor responded. "It fit in with the rest of the protocell system and, presumably, played a fundamental role in forming a self-sustaining, and self-perpetuating, system."

"Wouldn't you say this is a matter of twenty-twenty hindsight?" challenged Mr. Tappin. "Before one reached the stage of establishing even a primitive protocell, one would have to assume the beta-ribofuranose nucleoside is being selected.

"One cannot use the functioning of a system," argued the lawyer, "which has not yet been established as the reason for why such a molecule is being selected. So, why is this particular molecule, among all the other possibilities, being selected for, prior to the existence of a working protocell?"

"One can only assume," the professor stated, "that this particular nucleoside must have satisfied certain thermodynamic and kinetic contingencies which existed during the Archean era."

"Are the identities of these contingencies to be kept anonymous at this time, Professor?"

"I'm afraid so," acknowledged the professor. "I should point out, however, that Albert Eschenmoser, of the Swiss Federal Institute of Technology, has made several contributions relatively recently that bear on some of the issues we have been discussing."

"Yes, please go on," the lawyer requested.

"First of all," Dr. Yardley stated, "Eschenmoser constructed a molecule, known as pyranosyl RNA. This compound contains a modified form of naturally occurring ribose.

"The ribose that occurs in normal RNA contains a five member ring, consisting of 4 carbon atoms and one oxygen atom. The ribose molecule which forms part of Eschenmoser's pyranosyl RNA compound has been constructed to allow an extra carbon atom in the ring.

"Like normal RNA, complementary strands of pyranosyl RNA are capable of joining together by means of Watson-Crick hydrogen bonding. Furthermore, the use of pyranosyl RNA, with its modified form of ribose, prevents fewer unwanted variations of nucleoside structure from among the multiplicity of available possibilities than does normal RNA.

"In addition, double-strands of pyranosyl RNA do not twist around one another, as is the case with the normal forms of double-stranded RNA. This quality could be extremely important if enzymes were not available, unlike the situation currently, to unwind these strands so that replication could take place."

"Dr. Yardley, as far as you know, does pyranosyl RNA exist outside the laboratory?" the defense counsel asked.

"No," the professor admitted.

"Would I be fair in saying, Professor," Mr. Tappin queried, "that although one might agree the pyranosyl RNA molecule which has been created in the laboratory is very interesting and suggestive of possibilities, nevertheless, this molecule really is of little practical import to origin-of-life issues if it, or something similar to it, did not exist in the Archean era?"

"Yes, this would be a fair way of saying things," agreed the professor.

"Moreover," added Mr. Tappin, "even if one were to suppose such a molecule as pyranosyl RNA existed in prebiotic times, one would have to explain why, and how, a molecule - namely, normal RNA - which, from a number of different perspectives, would not have had anywhere near the selective value of pyranosyl RNA, would have come to replace the latter molecule. Would you say these are fair issues to raise?"

"I suppose so," the professor offered.

"Can either of these problems be resolved at the present time," inquired Mr. Tappin.

"Not satisfactorily," responded the professor.

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