Theoretical origin of life; James Tour again (Introduction)

by David Turell , Saturday, August 05, 2017, 21:24 (2667 days ago) @ David Turell

He is a synthetic biochemist who knows how difficult it is to make any organic chemistry molecule. He has been quoted before:

http://inference-review.com/article/an-open-letter-to-my-colleagues

"Synthetic constraints must be taken into account when considering the prebiotic preparation of the four classes of compounds needed for life: the amino acids, the nucleotides, the saccharides, and the lipids.1 The next level beyond synthesis involves the components needed for the construction of nanosystems, which are then assembled into a microsystem. Composed of many nanosystems, the cell is nature’s fundamental microsystem. If the first cells were relatively simple, they still required at least 256 protein-coding genes. This requirement is as close to an absolute as we find in synthetic chemistry. A bacterium which encodes 1,354 proteins contains one of the smallest genomes currently known.

***

"coding information is essential. DNA and RNA are the primary informational carriers of the cell. No matter the medium life might have adopted at the very beginning, its information had to come from somewhere. A string of nucleotides does not inherently encode anything.

***

"Researchers have identified thousands of different lipid structures in modern cell membranes. These include glycerolipids, sphingolipids, sterols, prenols, saccharolipids, and polyketides. When making synthetic vesicles—synthetic lipid bilayer membranes—mixtures of lipids can destabilize the system.

"Lipid bilayers surround subcellular organelles, such as nuclei and mitochondria, which are themselves nanosystems and microsystems. Each of these has their own lipid composition.

"Lipids have a non-symmetric distribution. The outer and inner faces of the lipid bilayer are chemically inequivalent and cannot be interchanged.

"The lipids are just the beginning. Protein–lipid complexes are the required passive transport sites and active pumps for the passage of ions and molecules through bilayer membranes, often with high specificity. Some allow passage for substrates into the compartment, and others their exit. The complexity increases further because all lipid bilayers have vast numbers of polysaccharide (sugar) appendages, known as glycans, and the sugars are no joke. These are important for nanosystem and microsystem regulation. The inherent complexity of these saccharides is daunting. Six repeat units of the saccharide D-pyranose can form more than one trillion different hexasaccharides through branching (constitutional) and glycosidic (stereochemical) diversity.

"Polysaccharides are the most abundant organic molecules on the planet. Their importance is reflected in the fact that they are produced by and are essential to all natural systems. Every cell membrane is coated with a complex array of polysaccharides, and all cell-to-cell interactions take place through saccharide participation on the lipid bilayer membrane surface. Eliminating any class of saccharides from an organism results in its death, and every cellular dysfunction involves saccharides.

***

"very little is known about glycan diversification during evolution. Over three billion years of evolution has failed to generate any kind of living cell that is not covered with a dense and complex array of glycans.

"What is more, Vlatka Zoldoš, Tomislav Horvat, and Gordan Lauc observed: “A peculiarity of glycan moieties of glycoproteins is that they are not synthesized using a direct genetic template. Instead, they result from the activity of several hundreds of enzymes organized in complex pathways.” (my bold)

***

"Polysaccharides carry more potential information than any other macromolecule, including DNA and RNA. For this reason, lipid-associated polysaccharides are proving enigmatic.

"Cellular and organelle bilayers, which were once thought of as simple vesicles, are anything but. They are highly functional gatekeepers. By virtue of their glycans, lipid bilayers become enormous banks of stored, readable, and re-writable information.

***

"Many of the molecular structures needed for life are not thermodynamically favored by their syntheses. Formed by the formose reaction, the saccharides undergo further condensation under the very reaction conditions in which they form. The result is polymeric material, not to mention its stereo-randomness at every stereogenic center, therefore doubly useless.Time is the enemy. The reaction must be stopped soon after the desired product is formed.

***

"We synthetic chemists should state the obvious. The appearance of life on earth is a mystery. We are nowhere near solving this problem. The proposals offered thus far to explain life’s origin make no scientific sense.

***

"The laws of physics and chemistry’s Periodic Table are universal, suggesting that life based upon amino acids, nucleotides, saccharides and lipids is an anomaly. Life should not exist anywhere in our universe. Life should not even exist on the surface of the earth."

Comment: With his background struggling in the lab to synthesize, his point just above is valid. He is describing what is in the simplest of bacteria. Note my bold about glycoproteins being generated by a series of enzymes, not genes. Evolution did not find that system by chance.