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Abiogenesis enigma: Protein’s origin

Proteins

As you might know, proteins are one of the major “building blocks” of cells; there’s up to 10.000 different types of proteins, all manufactured inside each cell. Abiogenesis theorists  obviously supports the view that these molecules have arisen “by chance”, in a prebiotic world, billion years ago, however, to date, they have absolutely no clue about it, as we can read from this article:

“Proteins are the most complex chemicals synthesized in nature and must fold into complicated three-dimensional structures to become active. This poses a particular challenge in explaining their evolution from non-living matter. So far, efforts to understand protein evolution have focused on domains, independently folding units from which modern proteins are formed. Domains however are themselves too complex to have evolved de novo in an abiotic environment. We think that domains arose from the fusion of shorter, non-folding peptides, which evolved as cofactors supporting a primitive, RNA-based life form (the ‘RNA world’).” 1

So, why is it so complicated to explain its origin? Despite the often repeated innuendo that life and all of its components has “assuredly” originated through natural means, the clear failure of scientists to solve this puzzle can be easily explained by some truths about proteins, its synthesis, structure and so on. After that, no one can reasonably take its abiogenetic origin as logically granted. These truths also explain without shadow of doubt the intriguing fact that absolutely no single protein (even the lesser one, composed of only 8 amino acids) has ever been observed to appear anywhere in the world, outside the cells and high-tech labs, of course!

What’s a protein?

“Proteins are large biological molecules consisting of one or more chains of amino acids. Proteins perform a vast array of functions within living organisms, including catalyzing metabolic reactionsreplicating DNAresponding to stimuli, and transporting molecules from one location to another. Proteins differ from one another primarily in their sequence of amino acids, which is dictated by the nucleotide sequence of their genes, and which usually results in folding of the protein into a specific three-dimensional structure that determines its activity.

A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of adjacent amino acid residues. The sequence of amino acids in a protein is defined by the sequence of a gene, which is encoded in the genetic code. In general, the genetic code specifies 20 standard amino acids;” 2

Talking about amino acids, we’d like to recall another crucial problem for abiogenesis: The absence of self-occurring homochiral mixtures. As it has been told in a previous article, the laws of thermodynamics obliges the occurrence of racemic mixtures, ever:

“The left and right handed forms have identical free energy (G), so the free energy difference (ΔG) is zero. The equilibrium constant for any reaction (K) is the equilibrium ratio of the concentration of products to reactants. The relationship between these quantities at any Kelvin temperature (T) is given by the standard equation:

K = exp (–ΔG/RT)

where R is the universal gas constant (= Avogadro’s number x Boltzmann’s constant k) = 8.314 J/K.mol.

For the reaction of changing left-handed to right-handed amino acids (L → R), or the reverse (R → L), ΔG = 0, so K = 1. That is, the reaction reaches equilibrium when the concentrations of R and L are equal; that is, a racemate is produced.”

Therefore, any abiogenetic theorist has this astounding problem to deal with from the very beginning; without homochiral monomers, we can have zero possibility of a ‘magic’ protein self-assembling…

 

Protein synthesis

 

It’s quite uncanny that intelligent people with advanced knowledge on the subject might attempt to conceive hypothesis of such molecules originating spontaneously, in the wild and morbid inorganic environment, because for cells to build proteins, an intricate, complex and laborious process must take place!

 

 

First, genetic information is needed:

“Proteins are assembled from amino acids using information encoded in genes. Each protein has its own unique amino acid sequence that is specified by the nucleotide sequence of the gene encoding this protein. The genetic code is a set of three-nucleotide sets called codons and each three-nucleotide combination designates an amino acid (for example AUG (adenineuracilguanine) is the code for methionine).”

 

Many proteins use more that one of the 64 possible codons to be built. Moreover, that specific genetic code must be first translated, transcribed:

“Genes encoded in DNA are first transcribed into pre-messenger RNA (mRNA) by proteins such as RNA polymerase. Most organisms then process the pre-mRNA (also known as a primary transcript) using various forms of Post-transcriptional modification to form the mature mRNA, which is then used as a template for protein synthesis by the ribosome.”

Oh great, a bit complicated, isn’t it? Please, read the Wikipedia article referring to the messenger RNA, for further comprehension of what it is, its manufacturing, composition, etc; all of which adds up more complexity for the protein origin’s explanation.

 

 

The process of synthesizing a protein from an mRNA template is known as translation. The mRNA is loaded onto the ribosome and is read three nucleotides at a time by matching each codon to its base pairing anticodon located on a transfer RNA molecule, which carries the amino acid corresponding to the codon it recognizes. The enzyme aminoacyl tRNA synthetase “charges” the tRNA molecules with the correct amino acids. The growing polypeptide is often termed the nascent chain. Proteins are always biosynthesized from N-terminus to C-terminus.[6]

The size of a synthesized protein can be measured by the number of amino acids it contains and by its total molecular mass, which is normally reported in units of daltons (synonymous with atomic mass units), or the derivative unit kilodalton (kDa). Yeast proteins are on average 466 amino acids long and 53 kDa in mass.[5] The largest known proteins are the titins, a component of the muscle sarcomere, with a molecular mass of almost 3,000 kDa and a total length of almost 27,000 amino acids.[8]

 

Phew! How complicated! You may ask now: are we finally done? And I reply you: Huh, nope! Now that the ribosome, together with the rRNA and more than 50 other proteins, has finally finished the process, a protein is formed. However, it is always found in a  random coil shape. So what? This shape is mostly useless for its usage on organism, as we can read:

Each protein exists as an unfolded polypeptide or random coil when translated from a sequence of mRNA to a linear chain of amino acids. This polypeptide lacks any stable (long-lasting) three-dimensional structure (the left hand side of the neighbouring figure). 3

In that randomly coiled shape, the protein is highly unstable, breakable, useless for cell building, so, for proper biological use and better stability, the protein folding process must take place. This 3D-shape is known as the native state.

The correct three-dimensional structure is essential to function, although some parts of functional proteins may remain unfolded.[4] Failure to fold into native structure generally produces inactive proteins, but in some instances misfolded proteins have modified or toxic functionality. Several neurodegenerative and other diseases are believed to result from the accumulation of amyloid fibrils formed by misfolded proteins.[5] Many allergies are caused by incorrect folding of some proteins, for the immune system does not produce antibodies for certain protein structures.[6]

Another importance of the protein folding is:

 

Minimizing the number of hydrophobic side-chains exposed to water is an important driving force behind the folding process.[9] Formation of intramolecular hydrogen bonds provides another important contribution to protein stability.[10] 

 

And how does the folding occurs?

 

 

The amino-acid sequence of a protein determines its native conformation.[7] A protein molecule folds spontaneously during or after biosynthesis. While these macromolecules may be regarded as “folding themselves“, the process also depends on the solvent (water or lipid bilayer),[8] the concentration of salts, the pH, the temperature, the possible presence of cofactors and of molecular chaperones.

The process of folding often begins co-translationally, so that the N-terminus of the protein begins to fold while the C-terminal portion of the protein is still beingsynthesized by the ribosome. Specialized proteins called chaperones assist in the folding of other proteins.

Although most globular proteins are able to assume their native state unassisted, chaperone-assisted folding is often necessary in the crowded intracellular environment to prevent aggregation; chaperones are also used to prevent misfolding and aggregation that may occur as a consequence of exposure to heat or other changes in the cellular environment.

There are two models of protein folding that are currently being confirmed: The first: The diffusion collision model, in which a nucleus is formed, then the secondary structure is formed, and finally these secondary structures are collided together and pack tightly together. The second: The nucleation-condensation model, in which the secondary and tertiary structures of the protein are made at the same time. Recent studies have shown that some proteins show characteristics of both of these folding models.

The essential fact of folding, however, remains that the amino acid sequence of each protein contains the information that specifies both the native structure and the pathway to attain that state. Folding is a spontaneous process independent of energy inputs from nucleoside triphosphates. The passage of the folded state is mainly guided by hydrophobic interactions, formation of intramolecular hydrogen bonds, and van der Waals forces, and it is opposed by conformational entropy.

Only after the folding process, we have an useful, stable protein, with a properly designed shape with its up to four layers, so that the molecule can perform its biological function.

But, remember, many conditions and external factors can destroy proteins, such as hydrolysis (it’s a slow, but ceaseless process, because proteins are metastable, hydrophobic) and others:

Under some conditions proteins will not fold into their biochemically functional forms. Temperatures above or below the range that cells tend to live in will cause thermally unstableproteins to unfold or “denature” (this is why boiling makes an egg white turn opaque). High concentrations of solutes, extremes of pH, mechanical forces, and the presence of chemical denaturants can do the same.

A fully denatured protein lacks both tertiary and secondary structurel. Under certain conditions some proteins can refold; however, in many cases, denaturation is irreversible.[15] Cells sometimes protect their proteins against the denaturing influence of heat with enzymes known as chaperones or heat shock proteins, which assist other proteins both in folding and in remaining folded. Some proteins never fold in cells at all except with the assistance of chaperone molecules, which either isolate individual proteins so that their folding is not interrupted by interactions with other proteins or help to unfold misfolded proteins, giving them a second chance to refold properly. This function is crucial to prevent the risk of precipitation into insoluble amorphous aggregates.

 

For a further an in-depth study about different factors capable of disrupting proteins, read the following articles:

https://en.wikipedia.org/wiki/Protein_biosynthesis

http://creation.com/native-folds-in-polypeptide-chains-1 (a series of 6 parts)

 

To conclude our observation, it’s impossible not to be sceptic of any theoretic proposition that claims self-caused origin of proteins, because it turns out that science unveiled tons of facts that easily prevent any possibility of such proposed scenario:

 

-Absence of homochiral monomers forming in the environment;

-Necessity of genetic specific information;

-Need for an highly controlled ambient, with proper Ph level, temperature, absence of mechanical forces that may easily damage, disrupt the protein, toxins, etc; 

-Need for specific methods to protect the protein against hydrolysis, oxidation;

-Necessity of having 50 other types of protein already manufactured to help on the protein synthesis;

 

The question raises: how in the world could such a specific set of conditions be found in a prebiotic Earth? Such condition can only be barely found in a first-class laboratory, driven by qualified and experienced scientists!

You might as well enjoy watching this short video talking about protein synthesis:

 

References

1. <http://www.eb.tuebingen.mpg.de/research/departments/protein-evolution/protein-evolution.html>

2. <https://en.wikipedia.org/wiki/Protein>

3. <https://en.wikipedia.org/wiki/Protein_folding>

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DNA- fascinating video

Deoxyribonucleic acid (DNA) is a molecule that encodes the genetic instructions used in the development and functioning of all known living organisms and many viruses. Along with RNA and proteins, DNA is one of the three major macromolecules essential for all known forms of life. Most DNA molecules are double-stranded helices, consisting of two long biopolymers of simpler units called nucleotides—each nucleotide is composed of a nucleobase (guanine, adenine, thymine, and cytosine), recorded using the letters G, A, T, and C, as well as a backbone made of alternating sugars (deoxyribose) and phosphate groups (related to phosphoric acid), with the nucleobases (G, A, T, C) attached to the sugars. DNA is well-suited for biological information storage, since the DNA backbone is resistant to cleavage and the double-stranded structure provides the molecule with a built-in duplicate of the encoded information. The following video shows animations of processes which occur within each one of the 10 trillion cells in our body!

Discovery

In 1927, Nikolai Koltsov proposed that inherited traits would be inherited via a “giant hereditary molecule” made up of “two mirror strands that would replicate in a semi-conservative fashion using each strand as a template”. In 1928, Frederick Griffith discovered that traits of the “smooth” form of Pneumococcus could be transferred to the “rough” form of the same bacteria by mixing killed “smooth” bacteria with the live “rough” form. This system provided the first clear suggestion that DNA carries genetic information—the Avery–MacLeod–McCarty experiment—when Oswald Avery, along with coworkers Colin MacLeod and Maclyn McCarty, identified DNA as the transforming principle in 1943. DNA’s role in heredity was confirmed in 1952, when Alfred Hershey and Martha Chase in the Hershey–Chase experiment showed that DNA is the genetic material of the T2 phage.

In 1953, James Watson and Francis Crick suggested what is now accepted as the first correct double-helix model of DNA structure in the journal Nature. Their double-helix, molecular model of DNA was then based on a single X-ray diffraction image (labeled as “Photo 51”) taken by Rosalind Franklin and Raymond Gosling in May 1952, as well as the information that the DNA bases are paired — also obtained through private communications from Erwin Chargaff in the previous years. Chargaff’s rules played a very important role in establishing double-helix configurations for B-DNA as well as A-DNA.

Experimental evidence supporting the Watson and Crick model was published in a series of five articles in the same issue of Nature. Of these, Franklin and Gosling’s paper was the first publication of their own X-ray diffraction data and original analysis method that partially supported the Watson and Crick model; this issue also contained an article on DNA structure by Maurice Wilkins and two of his colleagues, whose analysis and in vivo B-DNA X-ray patterns also supported the presence in vivo of the double-helical DNA configurations as proposed by Crick and Watson for their double-helix molecular model of DNA in the previous two pages of Nature.

Repairing system

It’s interesting to notice that the DNA molecule is highly reactive, thus, very unstable… On a good day about one million bases in the DNA in a human cell are damaged. These lesions are caused by a combination of normal chemical activity within the cell and exposure to radiation and toxins coming from environmental sources including cigarette smoke, grilled foods and industrial wastes. So, the organisms have a handful of repairing mechanisms, as said in a recent Science Daily article:

A number of environmental toxins and chemotherapy drugs are alkylation agents that can attack DNA.

When a DNA base becomes alkylated, it forms a lesion that distorts the shape of the molecule enough to prevent successful replication. If the lesion occurs within a gene, the gene may stop functioning. To make matters worse, there are dozens of different types of alkylated DNA bases, each of which has a different effect on replication.

One method to repair such damage that all organisms have evolved is called base excision repair. In BER, special enzymes known as DNA glycosylases travel down the DNA molecule scanning for these lesions. When they encounter one, they break the base pair bond and flip the deformed base out of the DNA double helix. The enzyme contains a specially shaped pocket that holds the deformed base in place while detaching it without damaging the backbone. This leaves a gap (called an “abasic site”) in the DNA that is repaired by another set of enzymes.

Human cells contain a single glycosylase, named AAG, that repairs alkylated bases. It is specialized to detect and delete “ethenoadenine” bases, which have been deformed by combining with highly reactive, oxidized lipids in the body. However, AAG also handles many other forms of akylation damage. Many bacteria, however, have several types of glycosylases that handle different types of damage.

“It’s hard to figure out how glycosylases recognize different types of alkylation damage from studying AAG since it recognizes so many,” says Eichman. “So we have been studying bacterial glycosylases to get additional insights into the detection and repair process.”

That is how they discovered the bacterial glycosylase AlkD with its unique detection and deletion scheme. All the known glycosylases work in basically the same fashion: They flip out the deformed base and hold it in a special pocket while they excise it. AlkD, by contrast, forces both the deformed base and the base it is paired with to flip to the outside of the double helix. This appears to work because the enzyme only operates on deformed bases that have picked up an excess positive charge, making these bases very unstable. If left alone, the deformed base will detach spontaneously. But AlkD speeds up the process by about 100 times. Eichman speculates that the enzyme might also remain at the location and attract additional repair enzymes to the site.

AlkD has a molecular structure that is considerably different from that of other known DNA-binding proteins or enzymes. However, its structure may be similar to that of another class of enzymes called DNA-dependent kinases. These are very large molecules that possess a small active site that plays a role in regulating the cells’ response to DNA damage. AlkD uses several rod-like helical structures called HEAT repeats to grab hold of DNA. Similar structures have been found in the portion of DNA-dependent kinases with no known function, raising the possibility that they play an additional, unrecognized role in DNA repair.

It’s impossible to conceive that such unstable, complex molecule could have originated all alone, by chance and lasted any long in a pre-biotic environment. In a primordial Earth, with a free-oxygen atmosphere, it turns out that it would have no ozon layer, or a very thin one. Thus, the UV light from the Sun would freely bombards the Earth without filtering; the most damaging UV light types would face no barrier, and it’s a fact that UV light damages, degrades polymers!

Many natural and synthetic polymers are attacked by ultra-violet radiation and products made using these materials may crack or disintegrate (if they’re not UV-stable). The problem is known as UV degradation, and is a common problem in products exposed to sunlight. Continuous exposure is a more serious problem than intermittent exposure, since attack is dependent on the extent and degree of exposure.

Effect of UV exposure on polypropylene rope (the left one is damaged, the right one is a new rope)

Add to it the oxidation problem, hydrolysis, etc… Any natural origin of RNA/DNA is inconceivable!

Building blocks very instable

From: http://creation.com/origin-of-life-instability-of-building-blocks

 

by 

Evolutionary propaganda often understates the difficulty of a naturalistic origin of life. Production of traces of ‘building blocks’ is commonly equated with proving that they could have built up the required complicated molecules under natural conditions. The instability of ‘building blocks’ in non-biotic environments is usually glossed over.

The RNA/DNA base cytosine is not produced in spark discharge experiments. The proposed prebiotic productions are chemically unrealistic because the alleged precursors are unlikely to be concentrated enough, and they would undergo side reactions with other organic compounds, or hydrolyse. Cytosine itself is too unstable to accumulate over alleged geological ‘deep time’, as its half life for deamination is 340 years at 25°C.


Populist RNA-world propaganda

A pro-evolution booklet called Science and Creationism, recently released on the Internet by the National Academy of Sciences (NAS),1 summarized the origin of life section as follows:

‘For those who are studying the origin of life, the question is no longer whether life could have originated by chemical processes involving nonbiological components. The question instead has become which of many pathways might have been followed to produce the first cells.’ 2

No one disputes the existence of living organisms on earth, and that cells indeed are capable of using simple building blocks to generate the required complex biochemicals at the necessary time, location and concentration. The question is whether the massive co-ordination of the metabolic processes which perform such feats could have arisen without intelligent guidance and driven by only statistical and thermodynamic constraints.

The NAS book glosses over the enormous chemical and informational hurdles which must be jumped to go from non-living matter to even the simplest living cells (see also Q&A: Origin of Life).3,4,5 It’s not too surprising, considering the heavy atheistic bias of the NAS, which was documented in the journal Nature,6 and which was probably partly responsible for their demonstrable scientific unreliability in the area of origins.7 It is even less excusable to ignore the difficulties documented in their own journal—Proceedings of the National Academy of Sciences (PNAS), USA, as will be shown here.

Production of ‘building blocks of life’

Science and Creationism argued:

‘Experiments conducted under conditions intended to resemble those present on primitive Earth have resulted in the production of some of the chemical components of proteins, DNA, and RNA. Some of these molecules also have been detected in meteorites from outer space and in interstellar space by astronomers using radiotelescopes. Scientists have concluded that the “building blocks of life” could have been available early in Earth’s history.’2

Even if we granted that the ‘building blocks’ were available, it does not follow that they could actually build anything. For example, under plausible prebiotic conditions, the tendency is for biological macromolecules to break apart into the ‘building blocks’, not the other way round.8 Also, the ‘building blocks’ are likely to react in the wrong ways with other ‘building blocks’, for example, sugars and other carbonyl (>C=O) compounds react destructively with amino acids and other amino (–NH2) compounds, to form imines (>C=N), a common cause of browning in foods.9

Furthermore, some of the building blocks are very unstable. A good example is ribose, which is obviously essential for RNA, and hence for the RNA-world hypothesis of the origin of life.10 A team including the famous evolutionary origin-of-life pioneer Stanley Miller, in PNAS, found that the half life (t½) of ribose is only 44 years at pH 7.0 (neutral) and 0°C. It’s even worse at high temperatures—73 minutes at pH 7.0 and 100°C.11 This is a major hurdle for hydrothermal theories of the origin of life. Miller, in another PNAS paper, has also pointed out that the RNA bases are destroyed very quickly in water at 100°C—adenine and guanine have half lives of about a year, uracil about 12 years, and cytosine only 19 days.12

Most researchers avoid such hurdles with the following methodology: find a trace of compound X in a spark discharge experiment, claim ‘see, X can be produced under realistic primitive-earth conditions’. Then they obtain pure, homochiral, concentrated X from an industrial synthetic chemicals company, react it to form traces of the more complex compound Y. Typically, the process is repeated to form traces of Z from purified Y, and so on.13 In short, the evolutionists’ simulations have an unacceptable level of intelligent interference.14

Much of the populist evolutionary propaganda resembles the following hypothetical theory for the origin of a car:

‘Design is an unscientific explanation, so we must find a naturalistic explanation instead. Now, experiments have shown that one of the important building blocks of the car—iron—can be produced by heating naturally occurring minerals like hematite to temperatures which are found in some locations on earth. What’s more, iron can be shown to form thin sheets under pressures which are known to occur in certain geological formations ….’

If this seems far-fetched, then note that even the simplest self-reproducing cell, which has 482 genes,15 has a vastly higher information content than a car, yet self-reproduction is a pre-requisite for neo-Darwinian evolution.

Essential building block missing—cytosine

The evolutionary biochemist, Robert Shapiro, published a detailed study of the ‘prebiotic’ synthesis of cytosine in the Proceedings of the NAS.16 Previous studies of his had noted that neither adenine17 nor ribose18 were plausible prebiotic components of any self-replicating molecule, but the problems with cytosine are even worse. Together, these studies raise serious doubts about whether a prebiotic replicator with any Watson-Crick base pairing could have arisen abiotically.

Shapiro noted that not the slightest trace of cytosine has been produced in gas discharge experiments, and nor has it been found in meteorites. Thus, he notes, either it is extremely hard to synthesise, or it breaks down before detection. So ‘prebiotic’ productions of cytosine have always been indirect, and involve the methodology alluded to above. That is, cyanoacetylene (HC≡CC≡N) and cyanoacetaldehyde (H3CCOC≡N) have been found in some spark discharge experiments. Organic chemists have obtained pure and fairly strong solutions of each, and reacted each of them with solutions of other compounds which are allegedly likely to be found on a ‘primitive’ earth. Some cytosine is produced. This then apparently justifies experiments trying to link up pure and dry cytosine and ribose to form the nucleoside cytidine. However, these experiments have been unsuccessful (although analogous experiments with purines have produced 2% yields of nucleosides),19 despite a high level of investigator interference.

Unavailability of cytosine precursors

Shapiro also critiqued some of the ‘prebiotic’ cytosine productions. He pointed out that both cyanoacetylene and cyanoacetaldehyde are produced in spark discharge experiments with an unlikely methane/nitrogen (CH4/N2) mixture. The classical Miller experiment used ammonia (NH3), but NH3, H2O and hydrogen sulfide (H2S) greatly hindered cyanoacetylene and cyanoacetaldehyde formation. However, most evolutionists now believe that the primitive atmosphere was ‘probably dominated by CO2 and N2.’20

Furthermore, cyanoacetylene and cyanoacetaldehyde would undergo side reactions with other nucleophiles rather than produce cytosine. For example, cyanoacetylene and cyanoacetaldehyde both react with the amino group, which would destroy any prebiotic amino acids. And there is one destructive molecule which is unavoidably present: water. Cyanoacetylene readily hydrolyzes to form cyanoacetaldehyde (t½ = 11 days at pH 9, 30°C),20 although one should not count on this as a reliable source of cyanoacetaldehyde because cyanoacetylene would more likely be destroyed by other reactions.20 And cyanoacetaldehyde, while more stable than cyanoacetylene, is still quite quickly hydrolyzed (t½ = 31 years at pH 9, 30°C).21

The implausible production scenarios and likely rapid destruction means it is unrealistic to assume that the concentration of cyanoacetylene and cyanoacetaldehyde could remotely approach that needed to produce cytosine.

Instability of cytosine

As pointed out above, cytosine is deaminated/hydrolyzed (to uracil) far too rapidly for any ‘hot’ origin-of-life scenario. But it is still very unstable at moderate temperatures—t½ = 340 years at 25°C. This shows that a cold earth origin-of-life scenario would merely alleviate, but not overcome, the decomposition problem. And a low temperature also retards synthetic reactions as well as destructive ones.

On single-stranded DNA in solution, t½ of an individual cytosine residue = 200 years at 37°C, while the double helix structure provides good protection—t½ = 30,000 years.22 Such C→U mutations would be a great genetic hazard, but cells have an ingenious repair system involving a number of enzymes. It first detects the mutant U (now mismatched with G) and removes it from the DNA strand, opens the strand, inserts the correct C, and closes the strand.22 It seems that such a repair system would be necessary from the beginning, because a hypothetical primitive cell lacking this would mutate so badly that error catastrophe would result. And the far greater instability of cytosine on single-stranded nucleic acid is yet another problem that proponents of the RNA-world must account for.

Also, cytosine is readily decomposed under solar UV radiation, which requires that prebiotic synthesis should be carried out in the dark.21

An efficient prebiotic synthesis of cytosine?

This was claimed by Robertson and Miller.23 They rightly disagreed with a previous suggested synthesis of cytosine from cyanoacetylene and cyanate (OCN) because cyanate is rapidly hydrolyzed to CO2 and NH3. Instead, they heated 10-3 M cyanoacetaldehyde with various concentrations of urea ((NH2)2CO) in a sealed ampoule at 100 oC for five hours with 30-50% yields of cytosine. Urea is produced in spark discharge experiments with N2, CO and H2O.

However, Shapiro criticised this experiment on the grounds of the unavailability of cyanoacetaldehyde and instability of cytosine, as above. Robertson and Miller avoided the latter problem by stopping the reaction after five hours. But in a real prebiotic world, such a reaction would most likely continue with hydrolysis of cytosine.

Shapiro also shows that urea is too unstable to reach the concentrations required (>0.1 M). Urea exists in equilibrium with small amounts of its isomer, ammonium cyanate, and since cyanate is hydrolysed readily, more urea must convert to maintain the equilibrium ratio (K = 1.04 x 10-4 at 60°C).21 Robertson and Miller’s sealed tube thus provided a further example of unacceptable investigator interference, because this prevented escape of NH3, thus unrealistically retarding cyanate and urea decomposition. In an open system, ‘half of the urea was destroyed after 5 hr at 90 oC and pH 7’,21 and t½ is estimated at 25 years at 25°C.21

The usual cross-reaction problem would intervene in the real world. For example, urea can react with glycine to form N-carbamoyl glycine,21 which would remove both urea and amino acids from a primordial soup.

Also, the primordial soup would be far too dilute, so Robertson and Miller propose that seawater was concentrated by evaporation in lagoons. But this would require isolation of the lagoon from fresh seawater which would dilute the lagoon, evaporation to about 10–5 of its original volume, then cytosine synthesis. However, such conditions are geologically ‘rare or non-existent’ today.24 Concentrating mechanisms would also concentrate destructive chemicals.

The conditions required for cytosine production are incompatible with those of purine production. Therefore this scenario must also include a well-timed rupture of the lagoon, releasing the contents into the sea, so both pyrimidines and purines can be incorporated into a replicator.

Shapiro’s materialistic faith

Shapiro concluded:

‘the evidence that is available at the present time does not support the idea that RNA, or an alternative replicator that uses the current set of RNA bases, was present at the start of life.’ 25

But unwilling to abandon evolution, he suggests two alternative theories:

1. Cairns-Smith’s clay mineral idea,13 which seems to be driven more by dissatisfaction with other theories than evidence for his own.

‘Cairns-Smith cheerfully admits the failings of his pet hypothesis: no-one has been able to coax clay into something resembling evolution in the laboratory; nor has anyone found anything resembling a clay-based organism in nature.’26

[Update: recent research shows more difficulties with this idea: Darwin’s warm pond idea is tested, 13 February 2006:

‘Professor Deamer said that amino acids and DNA, the “building blocks” for life, and phosphate, another essential ingredient, clung to the surfaces of clay particles in the volcanic pools.

‘“The reason this is significant is that it has been proposed that clay promotes interesting chemical reactions relating to the origin of life,” he explained.

‘“However,” he added, “in our experiments, the organic compounds became so strongly held to the clay particles that they could not undergo any further chemical reactions.”’]

2. Life began as a cyclic chemical reaction, e.g. Günter Wächtershäuser’s theory that life began on the surface of pyrite, which Stanley Miller calls ‘paper chemistry’.27

‘Wächtershäuser himself admits that his theory is for the most part “pure speculation”.’28,29

Shapiro’s dogmatism is illustrated in his interesting popular-level book Origins: A Skeptic’s Guide to the Creation of Life in the Universe, where he effectively critiques many origin-of-life scenarios. But he says, in a striking admission that no amount of evidence would upset his faith:

‘some future day may yet arrive when all reasonable chemical experiments run to discover a probable origin of life have failed unequivocally. Further, new geological evidence may yet indicate a sudden appearance of life on the earth. Finally, we may have explored the universe and found no trace of life, or processes leading to life, elsewhere. Some scientists might choose to turn to religion for an answer. Others, however, myself included, would attempt to sort out the surviving less probable scientific explanations in the hope of selecting one that was still more likely than the remainder.’30

Conclusion

  • No plausible prebiotic synthesis of cytosine yet exists.
  • Vital ‘building blocks’ including cytosine and ribose are too unstable to have existed on a hypothetical prebiotic earth for long.
  • Even if cytosine and ribose could have existed, there is no known prebiotic way to combine them to form the nucleoside cytidine, even if we granted unacceptably high levels of investigator interference.
  • Building blocks would be too dilute to actually build anything, and would be subject to cross-reactions.
  • Even if the building blocks could have formed polymers, the polymers would readily hydrolyse.
  • There is no tendency to form the high-information polymers required for life as opposed to random ones.

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Further Reading

References

  1. Science and Creationism: A View from the National Academy of Sciences, Second Edition, <http://books.nap.edu/html/creationism/index.html&gt;, 28 July 1999. Return to text.
  2. <http://books.nap.edu/html/creationism/origin.html&gt;, 28 July 1999. Return to text.
  3. Aw, S.E., The origin of life: A critique of current scientific models , Journal of Creation 10(3):300–314, 1996. Return to text.
  4. Thaxton, C.B., Bradley, W.L. and Olsen, R.L., The Mystery of Life’s Origin, Philosophical Library Inc., New York, 1984. Return to text.
  5. Bird, W.R., The Origin of Species: Revisited, Thomas Nelson, Inc., Nashville, Tennessee, Vol. I Part III, 1991. Return to text.
  6. Larson, E.J. and Witham, L., Leading scientists still reject God, Nature 394(6691):313, 1998. The sole criterion for being classified as a ‘leading’ or ‘greater’ scientist was membership of the NAS. [See also National Academy of Science is godless to the core — survey — Ed.] Return to text.
  7. For example, the NAS teacher’s guidebook Teaching about Evolution and the Nature of Science, National Academy Press, Washington DC, 1998. This has been shown to be severely flawed by Sarfati, J.D.Refuting Evolution, Master Books, Green Forest, AR, USA, 1999. Return to text.
  8. Sarfati, J.D.Origin of life: the polymerization problemJournal of Creation 12(3):281–284, 1998. Return to text.
  9. Thaxton et al., Ref. 4, p. 51. Return to text.
  10. See Mills, G.C. and Kenyon, D.H., The RNA world: A critiqueOrigins and Design 17(1):9–16, 1996. Return to text.
  11. Larralde, R., Robertson, M.P. and Miller, S.L., Rates of decomposition of ribose and other sugars: Implications for chemical evolution, Proc. Natl. Acad. Sci. USA 92:8158–8160, 1995. Return to text.
  12. Levy, M and Miller, S.L., The stability of the RNA bases: Implications for the origin of life, Proc. Natl. Acad. Sci. USA 95(14):7933–38, 1998. Return to text.
  13. The evolutionist A.G. Cairns-Smith has raised the same objections against the typical ‘origin of life’ simulation experiments in his book Genetic Takeover and the Mineral Origins of Life, Cambridge University Press, New York, 1982—see extractReturn to text.
  14. Thaxton et al., Ref. 4, ch. 6. Return to text.
  15. Fraser, C.M., et al., The minimal gene complement of Mycoplasma genitalium, Science 270(5235):397–403, 1995; Perspective by Goffeau, A., Life with 482 genes, same issue, pp. 445–446. Return to text.
  16. Shapiro, R., Prebiotic cytosine synthesis: A critical analysis and implications for the origin of life, Proc. Natl. Acad. Sci. USA 96(8):4396–4401, 1999. Return to text.
  17. Shapiro, R., The prebiotic role of adenine: A critical analysis, Origins of Life and Evolution of the Biosphere 25:83–98, 1995. Return to text.
  18. Shapiro, R., Prebiotic ribose synthesis: A critical analysis, Origins of Life and Evolution of the Biosphere 18:71–85, 1988. Return to text.
  19. Orgel, L.E. and Lohrmann, R., Prebiotic chemistry and nucleic acid replication, Accounts of Chemical Research 7:368–377, 1974; cited in Cairns-Smith, Ref. 13, pp. 56–57. Return to text.
  20. Shapiro, Ref. 16, p. 4397. Return to text.
  21. Shapiro, Ref. 16, p. 4398. Return to text.
  22. Lindahl, T., Instability and decay of the primary structure of DNA, Nature 362(6422):709–715, 1993. Return to text.
  23. Robertson, M.P. and Miller, S.L., An efficient prebiotic synthesis of cytosine and uracil, Nature 375(6534):772–774; correction 377(6546):257. Return to text.
  24. Shapiro, Ref. 16, p. 4399. Return to text.
  25. Shapiro, Ref. 16, p. 4400. Return to text.
  26. Horgan, J., In the beginning, Scientific American 264(2):100–109, 1991; quote on p. 108. Return to text.
  27. Horgan, Ref. 26; Miller cited on p. 102. Return to text.
  28. Horgan, Ref. 26; Wächtershäuser cited on p. 106. Return to text.
  29. Sarfati, J.D.Ref. 8, extensively critiques one of Wächtershäuser’s latest experiments that supposedly supports his theory. Return to text.
  30. Shapiro, R., Origins: A Skeptic’s Guide to the Creation of Life in the Universe, Penguin, London, p. 130, 1986,1988. Shapiro then wishfully continues: ‘We are far from that state now.’Return to text.
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