The Limits of Organic Life in Planetary Systems (2007) / Chapter Skim
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4 Alternatives to Terran Biochemistry in Water
4 Alternatives to Terran Biochemistry in Water
Pages 43-52
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From page 43... ...
Furthermore, the exploitation of the polar versus nonpolar, hydrophilic versus hydrophobic, and water-soluble versus water-insoluble dichotomies in the construction of terran metabolites, macromolecules, and supramolecular structures appears to be an elegant way to solve problems that are presumably presented to life generally. The evident compatibility between terran biochemistry and water makes it difficult to distinguish cause and effect.
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From page 44... ...
That is directly related to the question, Are the biomolecular structures that we know in terran life the only structures that can possibly meet the functional demands of living systems? 4.1.1 Terran Nucleic Acids Are Not the Only Structures That Can Support Genetic-like Behavior In some cases, direct experimental evidence shows that the molecules found globally in terran biochemistry are not the only structures that can perform the functions that they perform in the life that we know.
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From page 45... ...
Indeed, it is even possible that a form of life based on nonstandard genetic molecules might be present on Earth, undetected by standard tools that detect standard DNA. Similar efforts in synthetic biology have shown that the ribose and deoxyribose sugars are not unique solutions to the need for a scaffolding in a linear genetic biopolymer.
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From page 46... ...
14 That result was obtained with the terran ribosome. 4.1.3 Implications of Synthetic Biology for Our View of the Universality of Global Terran Proteins and Nucleic Acids Work with synthetic biology makes it clear that the core set of nucleotides and the core set of amino acids found in all terran life inspected to date are not the only nucleotides and amino acids that can function in genetic and catalytic systems.
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From page 47... ...
18 Synthetic biologists have undertaken many efforts to create nonionic analogues of DNA and RNA. For example, replacing the anionic phosphate diester linker with the uncharged dimethylenesulfone linker generated DNA and RNA analogues that were rough isosteres of the phosphate analogue (Figure 4.2)
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From page 48... ...
Therefore, a repeating charge may be a universal structural feature of any genetic molecule that supports Darwinian evolution in water. Polycationic backbones may be as satisfactory as polyanionic backbones, however.
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From page 49... ...
They are famously the products of the Miller process by which methane, ammonia, and water were subjected to electrical discharge. And amino acids are found in carbonaceous meteorites both as alpha amino acids that are standard in terran life and as the nonstandard alpha-methylamino acids found by Cronin and Pizzarello.24 The uniqueness of bonding between carbon, oxygen, and nitrogen makes it difficult to conceive of an alternative backbone that contains a repeating dipole.
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From page 50... ...
The application of synthetic biology to construct biopolymers that could be suitable to planetary environments radically different from Earth's, such as at Titan, will require NASA missions that emphasize measurements of environmental properties that narrow the options for biopolymers. The principal challenge in designing research programs in this field is in the number of possible alternative structures that can be drawn on paper.
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From page 51... ...
ALTERNATIVES TO TERRAN BIOCHEMISTRY IN WATER H2 H2 NH2 NH2 NH2 CH3 NH2 H2 H2 C C CH C CH3 H3C CH C H3C C H3C CH CH H3C C C COOH C CH COOH C C COOH C C COOH H2 H2 H2 H2 H2 H2 H2 CH3 2-Amino- 2- Amino 2-Aminoheptanoic acid 2- Amino 2-methylhexanoic acid 3-methylhexanoic acid 4-methylhexanoic acid H2 NH2 NH2 CH3 NH2 CH3 NH2 H2 H3 C C CH C C CH3 CH C CH3 CH CH CH C COOH H3C CH COOH H3C C COOH H3C CH COOH H CH3 2 H2 CH3 CH3 2-Amino- 2-Amino-2,4-dimethyl 2-Amino-2,3-dimethyl- 2-Amino-3,4-dimethyl 5-methylhexanoic acid pentanoic acid pentanoic acid pentanoic acid H2 NH2 NH2 H2 NH2 H2 CH3 NH2 COOH C C CH C C CH H3C C CH H3C H3C CH COOH C CH2 H3C C COOH C COOH H2 H3C H2 CH2 H3C CH3 CH3 H3C 2-Amino-4,4-dimethyl 2-Amino-3,3-dimethyl- 2-Amino-2-ethyl 2-Amino-3-ethyl pentanoic acid pentanoic acid pentanoic acid pentanoic acid NH2 NH2 NH2 H2 H3C C COOH H3C H3C C COOH H3C C C COOH H3C CH COOH CH CH2 CH C CC CH3 H3C H H2 H2 CH3 CH3 NH2 2 3-Aminopentanoic acid 2-Amino-2,3, 3-trimethyl- 2-Amino-2-ethyl-3-methyl- 4-Aminopentanoic acid butanoic acid butanoic acid NH2 H2 CH3 H2 H2 NH2 CH COOH COOH C C COOH C CH H3C C C H2N C C H3C CH H2N C COOH H3C H2 H2 H2 H2 CH3 4-Amino-2-methyl 5-Aminopentanoic acid 3-Amino-2-methyl- 3-Amino-3-methyl butanoic acid butanoic acid butanoic acid H2 H2 H2 H2 H2 NH2 C COOH CC C CH3 H2N CH H3C C CH H2N CH COOH H2N C COOH C C COOH CH2 CH3 CH3 H2 H2 H3C 2-Aminopentanoic acid 4-Amino-3-methyl- 3-Amino-2,2-dimethyl 3-Amino-2-ethyl- (norleucine) butanoic acid propanoic acid propanoic acid H2 NH2 H2 H C NH2 C CH3 N COOH H2C HOOC C COOH C H3C C C COOH H2N C H2C C COOH H2 H2 H2 H2 Sarcosine 3-Aminopropanoic acid 2-Methylaspartic acid Cycloleucine FIGURE 4.5 Amino acids reported from carbonaceous chondrite meteorites.
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From page 52... ...
2004. Understanding nucleic acids using synthetic chemistry.
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