Theoretical origin of life; Chirality used by nature (Introduction)

by David Turell , Thursday, February 16, 2017, 01:30 (2623 days ago) @ David Turell

An organic chemist tries to explain the use of chirality in nature. All amino acids in life are left handed. DNA and RNA twist right handed:

http://inference-review.com/article/chiral-induced-spin-selectivity

"Chirality is ubiquitous in biological molecules. Aside from water, glycine, and acetic acid (among others), the majority of such molecules are chiral. The polymers of chiral molecules, such as the polysaccharides, polypeptides, and polynucleotides, are composed of chiral molecules. Such structures take on new shapes, including helices and spiral clefts, that are themselves chiral.

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"Chemists now know that chiral molecules act as electron spin filters, permitting the one-way passage of electrons of one spin in preference to electrons of the other spin. Selective transmission probabilities can be a hundred times larger in a chiral molecule than in a non-chiral molecule. For an electron of the proper spin, chiral molecules show far less backscattering of the electron; this in turn greatly reduces the heat released from the molecule during the electron’s passage. Lower heat affords any biological system an advantage.

"Scientists have often wondered why living creatures do not overheat while undertaking normal biochemical functions. The existence of exceedingly efficient biochemical routes is something like an a priori deduction. Kwabena Boahen estimated that a microelectronics processor functioning with the capacity of a human brain would need at least ten megawatts to operate. This is equivalent to the output of a small hydroelectric power plant. The human brain needs only about ten watts.

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:Might CISS help to explain biology’s secret to efficiency?

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"CISS reveals that more is going on, and it is not subtle in its influence. The attractive interactions between molecules of matched chirality can be higher by as much as one electron volt over their mirror images. This strongly favors enantioselection. Preferred chiral interaction is due to neighboring spin-spin interactions; the electrostatic potentials upon which they depend can interact at near the speed of light.

"Is this how nature accomplishes its ultra-high degree of precision in enantioselective synthesis? Namaan et al. suggest that this is so.

"The overall yield of biochemical processes in which CISS figures is often in excess of 99.99%. Astounding! In the laboratory, if the chemist achieves an eighty percent chemical yield after thorough optimization, he is usually satisfied. By controlling the spin on reactive chemical intermediates, CISS processes influence the course of chemical reactions so that they shovel their yields to one product instead of another. Reversing the spin interactions generates a different product.

"There are other mysteries in nature. Consider the electronic transfers that routinely occur in photosynthesis and respiration. In the laboratory, electron transfer distances are often on the order of 0.5 nanometers or less. Biological systems routinely transfer electrons over distances of the tens of nanometers. Chiral molecules may act as nanoscale conduits for the 100-fold enhanced transmission of these electrons, provided that the spin on the electron is matched to the particular chiral molecule through which it passes.

"There are still other mysteries. Consider how a repair-enzyme senses that there is damage to the DNA chain from a distance of tens of nanometers. How? It may well be by the transmission of electrons through the chiral DNA conduit. Is the plethora of molecule-molecular recognition events impacted by CISS?

"Probably."

Comment: Simple biochemistry results in 50/50 right and left handed products. This experienced chemist can achieve 80% one type with enhanced processes. Nature prefers 99%. We are given this in Nature which results in great efficiency in living processes. Luck or design? Without this starting point in biochemistry life would not have happened.