| 1. |
- Brandenburg, A., et al.
(author)
-
Homochiral Growth Through Enantiomeric Cross-Inhibition
- 2005
-
In: Origins of Life and Evolution of Biospheres. - : Springer Science and Business Media LLC. - 0169-6149 .- 1573-0875. ; 35:3, s. 225-241
-
Journal article (peer-reviewed)abstract
- The stability and conservation properties of a recently proposed polymerization model are studied. The achiral (racemic) solution is linearly unstable once the relevant control parameter (here the fidelity of the catalyst) exceeds a critical value. The growth rate is calculated for different fidelity parameters and cross-inhibition rates. A chirality parameter is defined and shown to be conserved by the nonlinear terms of the model. Finally, a truncated version of the model is used to derive a set of two ordinary differential equations and it is argued that these equations are more realistic than those used in earlier models of that form.
|
|
| 2. |
|
|
| 3. |
- Brandenburg, Axel
(author)
-
The Limited Roles of Autocatalysis and Enantiomeric Cross-Inhibition in Achieving Homochirality in Dilute Systems
- 2019
-
In: Origins of life and evolution of the biosphere. - : SPRINGER. - 0169-6149 .- 1573-0875. ; 49:1-2, s. 49-60
-
Journal article (peer-reviewed)abstract
- To understand the effects of fluctuations on achieving homochirality, we employ a Monte-Carlo method where autocatalysis and enantiomeric cross-inhibition, as well as racemization and deracemization reactions are included. The results of earlier work either without autocatalysis or without cross-inhibition are reproduced. Bifurcation diagrams and the dependencies of the number of reaction steps on parameters are studied. In systems with 30,000 molecules, for example, up to a billion reaction steps may be needed to achieve homochirality without autocatalysis.
|
|
| 4. |
- Hammarström, Per, et al.
(author)
-
An Auto-Catalytic Surface for Conformational Replication of Amyloid Fibrils-Genesis of an Amyloid World?
- 2011
-
In: Origins of life and evolution of the biosphere. - : Springer Verlag (Germany). - 0169-6149 .- 1573-0875. ; 41:4, s. 373-383
-
Journal article (peer-reviewed)abstract
- Amyloid fibrils are composed of self assembled stacked peptide or protein molecules folded and trapped in a stable cross-beta-sheet conformation. The amyloid fibrillation mechanism represents an intriguing self-catalyzed process rendering replication of a molecular conformational memory of interest for prebiotic chemistry. Herein we describe how a solid surface can be rendered auto-catalytic for fibrillation of a protein solution. We have discovered that a hydrophobic silicon or glass surface can be made to continuously fibrillate solutions of insulin monomers under stressed conditions (pH 1.6, 65 degrees C). It was found that the surface acts as a platform for the formation of nascent seeds that induce fibril replication on and at the surface. This autocatalytic effect stems from a layer a few insulin molecules thick representing an oligomeric layer of misfolded, conformationally trapped, insulin molecules that rapidly through epitaxial growth catalyze the rate determining step (nucleation) during fibril replication. This autocatalytic layer is generated by the protein-solid surface interaction and conformational changes of the adsorbed protein during exposure at the air-water interface. The resulting autocatalytic surface thus both initiates local conformational molecular self-replication and acts as a reservoir for fibril seeds budding off into solution spreading fibril replication entities to the surrounding medium. The possibility of catalysis of the conformational replication process by minute amounts of nucleation sites located on a recruiting surface can evade the issue of dramatic concentration dependence of amyloidogenesis.
|
|
| 5. |
- Holm, Nils, et al.
(author)
-
Links between hydrothermal environments, pyrophosphate, Na+, and early evolution
- 2011
-
In: Origins of life and evolution of the biosphere. - : Springer Science and Business Media LLC. - 0169-6149 .- 1573-0875. ; 41:5, s. 483-493
-
Journal article (peer-reviewed)abstract
- The discovery that photosynthetic bacterial membrane-bound inorganic pyrophosphatase (PPase) catalyzed light-induced phosphorylation of orthophosphate (Pi) to pyrophosphate (PPi) and the capability of PPi to drive energy requiring dark reactions supported PPi as a possible early alternative to ATP. Like the proton-pumping ATPase, the corresponding membrane-bound PPase also is a H+-pump, and like the Na+-pumping ATPase, it can be a Na+-pump, both in archaeal and bacterial membranes. We suggest that PPi and Na+ transport preceded ATP and H+ transport in association with geochemistry of the Earth at the time of the origin and early evolution of life. Life may have started in connection with early plate tectonic processes coupled to alkaline hydrothermal activity. A hydrothermal environment in which Na+ is abundant exists in sediment-starved subduction zones, like the Mariana forearc in the W Pacific Ocean. It is considered to mimic the Archean Earth. The forearc pore fluids have a pH up to 12.6, a Na+-concentration of 0.7 mol/kg seawater. PPi could have been formed during early subduction of oceanic lithosphere by dehydration of protonated orthophosphates. A key to PPi formation in these geological environments is a low local activity of water.
|
|
| 6. |
|
|
| 7. |
|
|
| 8. |
- Plasson, Raphaël, et al.
(author)
-
Homochirality and the Need for Energy
- 2010
-
In: Origins of life and evolution of the biosphere. - : Springer Science and Business Media LLC. - 0169-6149 .- 1573-0875. ; 40, s. 93-110
-
Journal article (peer-reviewed)abstract
- The mechanisms for explaining how a stable asymmetric chemical system can be formed from a symmetric chemical system, in the absence of any asymmetric influence other than statistical fluctuations, have been developed during the last decades, focusing on the non-linear kinetic aspects. Besides the absolute necessity of self-amplification processes, the importance of energetic aspects is often underestimated. Going down to the most fundamental aspects, the distinction between a single object—that can be intrinsically asymmetric—and a collection of objects—whose racemic state is the more stable one—must be emphasized. A system of strongly interacting objects can be described as one single object retaining its individuality and a single asymmetry; weakly or non-interacting objects keep their own individuality, and are prone to racemize towards the equilibrium state. In the presence of energy fluxes, systems can be maintained in an asymmetric non-equilibrium steady-state. Such dynamical systems can retain their asymmetry for times longer than their racemization time.
|
|
| 9. |
|
|
| 10. |
|
|
| 11. |
- Nilson, Frans Peder
(author)
-
Possible impact of a primordial oil slick on atmospheric and chemical evolution
- 2002
-
In: Origins of Life and Evolution of the Biosphere. - 0169-6149. ; 32:3, s. 247-253
-
Journal article (peer-reviewed)abstract
- Low molecular weight liquid hydrocarbons from various sources, could have formed an oil layer covering the primeval ocean (present already 4.0-4.4 x 10(9) yr ago), preventing water from evaporating into the atmosphere. Water from other sources, precipitated by cold traps at higher altitude in the atmosphere, becomes trapped in the ocean. In a thereby more dry and presumably reducing atmosphere (before 3.9 x 10(9) yr ago) even more hydrocarbons, as well as reactive molecules will form. An oil layer can possibly act as a dry solvent for reactions, where the reactive molecules can produce monomers and condensing agents. Monomers and eventual polymers formed could become strongly concentrated at the oil-water interface, favouring molecular interactions at high mobility and low dilution, without exposure to the destructive action of UV-light. Increased water leakiness of the oil layer due to accumulation of polar molecules within, would lead to photo-oxidation of liquid hydrocarbons, and subsequent emulsification at the oil-water interface, forming cellular structures. The atmosphere would then have lost its reducing character.
|
|
