Origin of life: latest theories/problems
by Rich Deem

Introduction

Early theories of the origin of life centered on the ability of a reducing atmosphere of the prebiotic earth to instigate formation of A group of 20 different kinds of small molecules that link together in long chains to form proteins. Often referred to as the "building blocks" of proteins.amino acids, and subsequently assembly of Organic compounds made of amino acids arranged in a linear chain, joined together by peptide bonds between the carboxyl and amino groups of the adjacent amino acid residues.proteins. Stanley Miller demonstrated in 1953 that mixtures of reducing gases, thought to be present in the primordial earth, when subjected to electrical discharges, produced many organic compounds, including several A group of 20 different kinds of small molecules that link together in long chains to form proteins. Often referred to as the "building blocks" of proteins.amino acids. Years later, a meteor which landed in Murchison, Australia, was shown to contain the same organic compound and A group of 20 different kinds of small molecules that link together in long chains to form proteins. Often referred to as the "building blocks" of proteins.amino acids in roughly the same proportion as those generated through the Miller experiments.

Homochirality

Although the Miller experiments and the Murchison meteor suggested that organic molecules could be synthesized in the absence of life, many questions and problems arose. Although simple Organic compounds made of amino acids arranged in a linear chain, joined together by peptide bonds between the carboxyl and amino groups of the adjacent amino acid residues.proteins could be produced by laboratory manipulations of A group of 20 different kinds of small molecules that link together in long chains to form proteins. Often referred to as the "building blocks" of proteins.amino acidbuilding blocks, no model or method of self replication of Organic compounds made of amino acids arranged in a linear chain, joined together by peptide bonds between the carboxyl and amino groups of the adjacent amino acid residues.proteins could be found. In addition, the A group of 20 different kinds of small molecules that link together in long chains to form proteins. Often referred to as the "building blocks" of proteins.amino acids which compose all forms of life are exclusively of the "left-handed" variety (L- A group of 20 different kinds of small molecules that link together in long chains to form proteins. Often referred to as the "building blocks" of proteins.amino acids). Those produced in the Miller experiments and found in the Murchison meteor are both L- and R- A group of 20 different kinds of small molecules that link together in long chains to form proteins. Often referred to as the "building blocks" of proteins.amino acids. No model could be proposed which would explain inclusion of only one form of A group of 20 different kinds of small molecules that link together in long chains to form proteins. Often referred to as the "building blocks" of proteins.amino acids to the exclusion of the other, without the aid of Ribonucleic acid: a chemical that directs the manufacture of proteins and sometimes codes for the genetic material within certain organisms.RNA's, in the form of Relating to ribosomes, complexes of RNA and protein that function in the translation of RNA into protein.ribosomal Ribonucleic acid: a chemical that directs the manufacture of proteins and sometimes codes for the genetic material within certain organisms.RNA (rRNA), transfer Ribonucleic acid: a chemical that directs the manufacture of proteins and sometimes codes for the genetic material within certain organisms.RNA ( A small RNA molecule that transfers a specific amino acid to a growing polypeptide chain at the ribosomal site of protein synthesis.tRNA), and messenger Ribonucleic acid: a chemical that directs the manufacture of proteins and sometimes codes for the genetic material within certain organisms.RNA ( Messenger ribonucleic acid is a molecule of RNA encoding a chemical 'blueprint' for a protein product, which is transcribed from a DNA template, and carries this information to the sites of protein synthesis.mRNA). All models would require the spontaneous evolution of both Ribonucleic acid: a chemical that directs the manufacture of proteins and sometimes codes for the genetic material within certain organisms.RNA's and Organic compounds made of amino acids arranged in a linear chain, joined together by peptide bonds between the carboxyl and amino groups of the adjacent amino acid residues.proteins simultaneously. In addition, specific Organic compounds made of amino acids arranged in a linear chain, joined together by peptide bonds between the carboxyl and amino groups of the adjacent amino acid residues.proteins are required in combination with rRNA in order for other Organic compounds made of amino acids arranged in a linear chain, joined together by peptide bonds between the carboxyl and amino groups of the adjacent amino acid residues.proteins to be synthesized. This dilemma has led to statements, such as that of Leslie Orgel, "And so, at first glance, one might have to conclude that life could never, in fact, have originated by chemical means."

RNA World

To try to avoid the overwhelming problems associated with the self replication of Organic compounds made of amino acids arranged in a linear chain, joined together by peptide bonds between the carboxyl and amino groups of the adjacent amino acid residues.proteins, Carl Woese, Francis Crick, and Leslie Orgel proposed Ribonucleic acid: a chemical that directs the manufacture of proteins and sometimes codes for the genetic material within certain organisms.RNA as the original building blocks of life. They proposed that self-replicating Ribonucleic acid: a chemical that directs the manufacture of proteins and sometimes codes for the genetic material within certain organisms.RNA could code for Organic compounds made of amino acids arranged in a linear chain, joined together by peptide bonds between the carboxyl and amino groups of the adjacent amino acid residues.proteinsand eventually evolve into Deoxyribonucleic acid: the chemical inside the nucleus of a cell that carries the genetic instructions for making living organisms.DNA, because of Deoxyribonucleic acid: the chemical inside the nucleus of a cell that carries the genetic instructions for making living organisms.DNA's superior intrinsic stability. Experiments by several scientists have demonstrated the ability of Ribonucleic acid: a chemical that directs the manufacture of proteins and sometimes codes for the genetic material within certain organisms.RNA's to catalyze chemical reactions, similar to that seen by Proteins that encourage a biochemical reactions, usually speeding them up.enzymes (which are Organic compounds made of amino acids arranged in a linear chain, joined together by peptide bonds between the carboxyl and amino groups of the adjacent amino acid residues.proteins). But could Ribonucleic acid: a chemical that directs the manufacture of proteins and sometimes codes for the genetic material within certain organisms.RNAitself have been synthesized and replicated by chemical means on the prebiotic earth?

Problems getting the building blocks

Juan Oró discovered in 1961 that the nucleic acid base A purine base found in DNA and RNA, which pairs with thymine in DNA or with uracil in RNA.adenine could be synthesized in a mixture of hydrogen cyanide and ammonia. Since then, scientists have shown that the remaining nucleic acid bases, A purine base found in DNA and RNA, which pairs with cytosine in both DNA and RNA.guanine, A pyrimidine base found in RNA, which pairs with the complementary base adenine.uracil, and A pyrimidine base found in DNA and RNA, which pairs with guanine in both DNA and RNA.cytosine, could be synthesized from mixtures of hydrogen cyanide, cyanogen, and cyanoacetylene. When the nucleic acid bases are combined with the sugar ribose and phosphate, Structural components, or building blocks, of DNA and RNA. Nucleotides consists of a base plus a molecule of sugar and one of phosphate.nucleotides form, which in the presence of an appropriate catalyst, form random strands of Ribonucleic acid: a chemical that directs the manufacture of proteins and sometimes codes for the genetic material within certain organisms.RNA. The spontaneous formation of a self-replicating Ribonucleic acid: a chemical that directs the manufacture of proteins and sometimes codes for the genetic material within certain organisms.RNA (which acts as a catalyst for replication of itself) ensures perpetuation of the Ribonucleic acid: a chemical that directs the manufacture of proteins and sometimes codes for the genetic material within certain organisms.RNA, according to the theory.

It is at this point that the theory encounters major problems. First, there is no mechanism for the synthesis of ribose in the absence of Proteins that encourage a biochemical reactions, usually speeding them up.enzymes.1 All chemical reactions which synthesize ribose, produce it as a very minor product. The major products are other sugars, which combine with nucleic acids to form products which inhibit Ribonucleic acid: a chemical that directs the manufacture of proteins and sometimes codes for the genetic material within certain organisms.RNA synthesis and replication. In addition, any ribose formed is racemic, that is, both left- and right-handed. Only right-handed ribose can be used to form Structural components, or building blocks, of DNA and RNA. Nucleotides consists of a base plus a molecule of sugar and one of phosphate.nucleotides. Left-handed ribose interfers with Ribonucleic acid: a chemical that directs the manufacture of proteins and sometimes codes for the genetic material within certain organisms.RNA synthesis.

The next major problem is that Structural components, or building blocks, of DNA and RNA. Nucleotides consists of a base plus a molecule of sugar and one of phosphate.nucleotides do not form under prebiotic conditions. If the phosphate is left out, purine nucleosides ( A purine base found in DNA and RNA, which pairs with thymine in DNA or with uracil in RNA.adenine and A purine base found in DNA and RNA, which pairs with cytosine in both DNA and RNA.guanine) will form under these conditions, but no pyrimidine nucleosides ( A pyrimidine base found in DNA and RNA, which pairs with guanine in both DNA and RNA.cytosine and A pyrimidine base found in RNA, which pairs with the complementary base adenine.uracil) form. Even if a method for formation of pyrimidine nucleosides could be found, the combination of nucleosides with phosphate under prebiotic conditions produces not only Structural components, or building blocks, of DNA and RNA. Nucleotides consists of a base plus a molecule of sugar and one of phosphate.nucleotides, but other products which interfere with Ribonucleic acid: a chemical that directs the manufacture of proteins and sometimes codes for the genetic material within certain organisms.RNA polymerization and replication.

In order to get around the problems of One of the structural components, or building blocks, of DNA and RNA. A nucleotide consists of a base plus a molecule of sugar and one of phosphate.nucleotide formation, scientists have proposed that certain minerals may serve as catalysts for specific formation of only proper Structural components, or building blocks, of DNA and RNA. Nucleotides consists of a base plus a molecule of sugar and one of phosphate.nucleotides. To date, no such catalysts have been found.

Even if Structural components, or building blocks, of DNA and RNA. Nucleotides consists of a base plus a molecule of sugar and one of phosphate.nucleotides could be formed by some method, both right- and left-handed versions would be formed. When both right- and left-handed Structural components, or building blocks, of DNA and RNA. Nucleotides consists of a base plus a molecule of sugar and one of phosphate.nucleotides are added to RNA templates, replication is inhibited.

Which came first?

Beyond the problems of One of the structural components, or building blocks, of DNA and RNA. A nucleotide consists of a base plus a molecule of sugar and one of phosphate.nucleotide formation are still more problems regarding how Ribonucleic acid: a chemical that directs the manufacture of proteins and sometimes codes for the genetic material within certain organisms.RNA polymers might replicate in the absence of Organic compounds made of amino acids arranged in a linear chain, joined together by peptide bonds between the carboxyl and amino groups of the adjacent amino acid residues.proteins. The addition of Structural components, or building blocks, of DNA and RNA. Nucleotides consists of a base plus a molecule of sugar and one of phosphate.nucleotides will produce a complementary strand of Ribonucleic acid: a chemical that directs the manufacture of proteins and sometimes codes for the genetic material within certain organisms.RNA. However, there is, at present, no explanation for duplication of the original Ribonucleic acid: a chemical that directs the manufacture of proteins and sometimes codes for the genetic material within certain organisms.RNA polymer from the complementary strand, in the absence of Proteins that encourage a biochemical reactions, usually speeding them up.enzymes.

A key component of the Ribonucleic acid: a chemical that directs the manufacture of proteins and sometimes codes for the genetic material within certain organisms.RNA world hypothesis, A purine base found in DNA and RNA, which pairs with thymine in DNA or with uracil in RNA.adenine, has its own problems:

  1. A purine base found in DNA and RNA, which pairs with thymine in DNA or with uracil in RNA.Adenine synthesis requires HCN concentrations of at least 0.01 M. It is completely unreasonable to expect these concentrations on the prebiotic earth.
  2. A purine base found in DNA and RNA, which pairs with thymine in DNA or with uracil in RNA.Adenine is susceptible to hydrolysis (the half-life for deamination at 37°C, pH 7, is about 80 years). Therefore, no A purine base found in DNA and RNA, which pairs with thymine in DNA or with uracil in RNA.adenine would ever be expected to accumulate in any kind of "prebiotic soup."
  3. The A purine base found in DNA and RNA, which pairs with thymine in DNA or with uracil in RNA.adenine- A pyrimidine base found in RNA, which pairs with the complementary base adenine.uracil interaction is weak and nonspecific, and, therefore, would never be expected to function in any specific recognition scheme under the chaotic conditions of a "prebiotic soup."2

Similar problems apply to the abiotic synthesis of A pyrimidine base found in DNA and RNA, which pairs with guanine in both DNA and RNA.cytosine:

  1. A pyrimidine base found in DNA and RNA, which pairs with guanine in both DNA and RNA.Cytosine has never been found in any meteorites.
  2. A pyrimidine base found in DNA and RNA, which pairs with guanine in both DNA and RNA.Cytosine is not produced in electric spark discharge experiments using simulated "early earth atmosphere."
  3. Synthesis based upon cyanoacetylene requires the presence of large amounts of methane and nitrogen, however, it is unlikely that significant amounts of methane were present at the time life originated.
  4. Synthesis based upon cyanate is problematical, since it requires concentrations in excess of 1 M (molar). When concentrations of 0.1 M (still unrealistically high) are used, no A pyrimidine base found in DNA and RNA, which pairs with guanine in both DNA and RNA.cytosine is produced.
  5. Synthesis based upon cyanoacetaldehyde and urea suffers from the problem of deamination of the A pyrimidine base found in DNA and RNA, which pairs with guanine in both DNA and RNA.cytosine in the presence of high concenrations of urea (low concentrations produce no A pyrimidine base found in DNA and RNA, which pairs with guanine in both DNA and RNA.cytosine). In addition, cyanoacetaldehyde is reactive with a number of prebiotic chemicals, so would never attain reasonable concentrations for the reaction to occur. Even without the presence of other chemicals, cyanoacetaldehyde has a half-life of only 31 years in water.
  6. A pyrimidine base found in DNA and RNA, which pairs with guanine in both DNA and RNA.Cytosine deaminates with an estimated half-life of 340 years, so would not be expected to accumulate over time.
  7. Ultraviolet light on the early earth would quickly convert A pyrimidine base found in DNA and RNA, which pairs with guanine in both DNA and RNA.cytosine to its photohydrate and cyclobutane photodimers (which rapidly deaminate).3

According to Robert Shapiro, a prominent origin of life researcher, the spontaneous formation of a nucleic acid replicator is a "very improbable event." this is because the mixture of A group of 20 different kinds of small molecules that link together in long chains to form proteins. Often referred to as the "building blocks" of proteins.amino acids the Murchison meteorite show that there are many classes of prebiotic substances that would disrupt the necessary structural regularity of any replicator.4

In addition, all current synthesis schemes require concentration of reactants by a factor of at least 100,000. Robert Shapiro, in his analysis of the "drying lagoon" scenario said:

"If today's Earth may be taken as a model for the early one, then, cases of extreme lagoon concentration (to the extent needed to concentrate a solute by 105) are rare or nonexistent. This mechanism cannot be considered as a source that could stock a global ocean with a particular chemical."3

Conclusion Top of page

It is becoming increasingly apparent from over 40 years of research in the field, that the Ribonucleic acid: a chemical that directs the manufacture of proteins and sometimes codes for the genetic material within certain organisms.RNA model will never adequately explain life's origin. Increasingly, investigators are looking at alternative models, including pyranosyl Ribonucleic acid: a chemical that directs the manufacture of proteins and sometimes codes for the genetic material within certain organisms.RNA and A compound consisting of two or more amino acids, the building blocks of proteins.peptidenucleic acid polymers. These models, too, have major problems, which are probably insurmountable.

The current trend in origin of life research is to look for simpler, pre- Ribonucleic acid: a chemical that directs the manufacture of proteins and sometimes codes for the genetic material within certain organisms.RNAmolecules to serve as genetic material. These models will suffer the same fate as all the rest, namely, the incredible increase in information content required to produce self-replication is not possible in the time frame in which it was supposed to have occurred. The simpler the first step, the more likely it is to occur, but the harder it is to get from step one to step two.

Leslie Orgel recently stated, "The full details of how the Ribonucleic acid: a chemical that directs the manufacture of proteins and sometimes codes for the genetic material within certain organisms.RNA world, and life, emerged may not be revealed in the near future." Believers in Christ know that the Creator of life has already been revealed through the Bible. Even those who search for a creator other than God will, in fact, have the Creator of life revealed to them in the near future, for every knee shall bow and every tongue confess that Jesus Christ is Lord, to the glory of God the Father.



Related Materials Top of page

Origins of Life: Biblical and Evolutionary Models Face OffOrigins of Life: Biblical and Evolutionary Models Face Off by Fazale Rana and Hugh Ross. Probably the single most potent scientific argument against atheism is the problem with a naturalistic origin of life. This very problem led me to become a deist as a biology major at USC in the early 1970's. The problems for atheists have gotten no better since that time. In fact, the last 30+ years of research have turned up even more problems than those that existed when I first studied the theories. Fuz Rana (a biochemist) and Hugh Ross (an astrophysicist) have teamed up to write the definitive up-to-date analysis of the origin of life. The book examines the origins of life from the perspectives of chemistry, biochemistry, astronomy, and the Bible. A biblical creation model is presented along side the naturalistic models to help the reader decide which one fits the data better.


References Top of page

  1. Orgel, L. 1994. The origin of life on earth. Scientific American. 271 (4) p. 82.
  2. Shapiro, R. 1995. The prebiotic role of A purine base found in DNA and RNA, which pairs with thymine in DNA or with uracil in RNA.adenine: a critical analysis. Orig. Life Evol. Biosph. 25: 83-98 25: 83-98.
  3. Shapiro, R. 1999. Prebiotic A pyrimidine base found in DNA and RNA, which pairs with guanine in both DNA and RNA.cytosine synthesis: A critical analysis and implications for the origin of life. Proc. Natl.Acad. Sci. USA 96: 4396-4401.
  4. Shapiro, R. 2000. A replicator was not involved in the origin of life. IUBMB Life 49: 173-176.

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Last Modified June 21, 2001

 

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