The Perennial Riddle of Life’s Origin

2021 ◽  
pp. 82-96
Author(s):  
Franklin M. Harold
Keyword(s):  
Natural Selection ◽  
Electron Transport ◽  
Atp Synthase ◽  
Hydrothermal Vents ◽  
Rna World ◽  
Good Reason ◽  
Dynamic Network ◽  
Electron Transport Chains ◽  
The Origin Of Life

The origin of life is the most consequential problem in biology, possibly in all of science, and it remains unsolved. This chapter summarizes what has been learned and highlights questions that remain open, including How, Where, When, and especially Why. LUCA, some four billion years ago, already featured the basic capacities of contemporary cells. These must have evolved still earlier, at a nebulous proto-cellular stage. There is good reason to believe that enzymes, DNA, ribosomes, electron-transport chains, and the rotary ATP synthase all predate LUCA and were shaped by the standard process of variation and natural selection, but we know next to nothing about how cells ever got started. I favor the proposal that it began with a purely chemical dynamic network capable of reproducing itself, that may have originated by chance. Natural selection would have favored the incorporation of any ancillary factors that promoted its kinetic stability, especially ones that improved reproduction or gave access to energy. All the specifics are in dispute, including the role of a prebiotic broth of organic chemicals, the nature and origin of enclosure, the RNA world, and a venue in submarine hydrothermal vents. My sense is that critical pieces of the puzzle remain to be discovered.

Randomness and Complexity

2018 ◽  
Author(s):  
Steven E. Vigdor
Keyword(s):  
Quantum Mechanics ◽  
Natural Selection ◽  
Rna World ◽  
Biological Evolution ◽  
Variable Theory ◽  
Cosmological Natural Selection ◽  
Einstein Podolsky Rosen ◽  
World Hypothesis ◽  
Rna World Hypothesis

Chapter 7 describes the fundamental role of randomness in quantum mechanics, in generating the first biomolecules, and in biological evolution. Experiments testing the Einstein–Podolsky–Rosen paradox have demonstrated, via Bell’s inequalities, that no local hidden variable theory can provide a viable alternative to quantum mechanics, with its fundamental randomness built in. Randomness presumably plays an equally important role in the chemical assembly of a wide array of polymer molecules to be sampled for their ability to store genetic information and self-replicate, fueling the sort of abiogenesis assumed in the RNA world hypothesis of life’s beginnings. Evidence for random mutations in biological evolution, microevolution of both bacteria and antibodies and macroevolution of the species, is briefly reviewed. The importance of natural selection in guiding the adaptation of species to changing environments is emphasized. A speculative role of cosmological natural selection for black-hole fecundity in the evolution of universes is discussed.

scholarly journals Energy conservation under extreme energy limitation: the role of cytochromes and quinones in acetogenic bacteria

Extremophiles ◽  
2021 ◽  
Author(s):  
Florian P. Rosenbaum ◽  
Volker Müller
Keyword(s):  
Carbon Dioxide ◽  
Electron Transport ◽  
Metabolic Pathway ◽  
Enzyme Complex ◽  
Acetogenic Bacteria ◽  
Electron Transport Chains ◽  
Energy Limitation ◽  
Respiratory Chains

AbstractAcetogenic bacteria are a polyphyletic group of organisms that fix carbon dioxide under anaerobic, non-phototrophic conditions by reduction of two mol of CO2 to acetyl-CoA via the Wood–Ljungdahl pathway. This pathway also allows for lithotrophic growth with H2 as electron donor and this pathway is considered to be one of the oldest, if not the oldest metabolic pathway on Earth for CO2 reduction, since it is coupled to the synthesis of ATP. How ATP is synthesized has been an enigma for decades, but in the last decade two ferredoxin-dependent respiratory chains were discovered. Those respiratory chains comprise of a cytochrome-free, ferredoxin-dependent respiratory enzyme complex, which is either the Rnf or Ech complex. However, it was discovered already 50 years ago that some acetogens contain cytochromes and quinones, but their role had only a shadowy existence. Here, we review the literature on the characterization of cytochromes and quinones in acetogens and present a hypothesis that they may function in electron transport chains in addition to Rnf and Ech.

scholarly journals Molecular trade-offs in RNA ligases affected the modular emergence of complex ribozymes at the origin of life

2017 ◽  
Vol 4 (9) ◽  
pp. 170376
Author(s):  
Nisha Dhar ◽  
Marc S. Weinberg ◽  
Richard E. Michod ◽  
Pierre M. Durand
Keyword(s):  
Molecular Level ◽  
Rna World ◽  
Catalytic Efficiency ◽  
Molecular Size ◽  
Functional Flexibility ◽  
Trade Offs ◽  
The Origin Of Life ◽  
World Hypothesis ◽  
Rna World Hypothesis

In the RNA world hypothesis complex, self-replicating ribozymes were essential. For the emergence of an RNA world, less is known about the early processes that accounted for the formation of complex, long catalysts from small passively formed molecules. The functional role of small sequences has not been fully explored and, here, a possible role for smaller ligases is demonstrated. An established RNA polymerase model, the R18, was truncated from the 3′ end to generate smaller molecules. All the molecules were investigated for self-ligation functions with a set of oligonucleotide substrates without predesigned base pairing. The smallest molecule that exhibited self-ligation activity was a 40-nucleotide RNA. It also demonstrated the greatest functional flexibility as it was more general in the kinds of substrates it ligated to itself although its catalytic efficiency was the lowest. The largest ribozyme (R18) ligated substrates more selectively and with greatest efficiency. With increase in size and predicted structural stability, self-ligation efficiency improved, while functional flexibility decreased. These findings reveal that molecular size could have increased from the activity of small ligases joining oligonucleotides to their own end. In addition, there is a size-associated molecular-level trade-off that could have impacted the evolution of RNA-based life.

scholarly journals Origins of Life

2020 ◽  
pp. 2-7
Author(s):  
Hannah Mahoney
Keyword(s):  
Origin Of Life ◽  
Hydrothermal Vents ◽  
Rna World ◽  
Relevant Information ◽  
Future Research ◽  
Specific Chemical ◽  
Scientific Disciplines ◽  
Earth Environment ◽  
The Origin Of Life ◽  
Life On Earth

When, where, and how did life on Earth originate? The origin of life problem involves multiple scientific disciplines and has spanned multiple decades. It can be summarized into three stages: (1) the origin of biological monomers, (2) the origin of biological polymers, and (3) the emergence and evolution of cells. While highly speculative, the connections between these stages are theorized by attempting to determine the geochemical situations which could have driven chemical evolution and allow for the emergence of specific chemical functions of biological systems. This review summarizes reported findings relevant to the early Earth environment and the main theories in the origin of life subject. Specific focus is placed on the metabolism first, RNA world, and compartmentalization first theories as they are involved in the origin of life paradox. The review then discusses submarine hydrothermal vents as a possible location for which life could have occurred. Understanding of information pertaining to the origin of life is important as it allows for advancement and discoveries in other fields of science and medicine. Overall, the aim of this review is to display the relevant information about the origin of life theory and highlight the importance of future research.

Plastoquinones in photosynthesis

1978 ◽  
Vol 284 (1002) ◽  
pp. 591-599 ◽  
Keyword(s):  
Electron Transport ◽  
Photosystem Ii ◽  
Energy Conservation ◽  
Thylakoid Membrane ◽  
Electron Flow ◽  
Proton Translocation ◽  
Photosynthetic Electron Transport ◽  
Atp Formation ◽  
Electron Transport Chains

Several plastoquinones with different or modified side chains have been characterized in plant material: they are localized in the inner thylakoid membrane of the chloroplast. So far only plastoquinone-45 (PQ-45) has been identified as an obligatory functional component of the photosynthetic electron transport chain in chloroplasts between photosystem II and photosystem I. A special form (semiquinone) of PQ-45 acts as primary acceptor Q of photosystem II, a large pool of PQ-45 as electron buffer, interconnecting several electron transport chains. The rôle of PQ, in energy conservation (ATP formation) is of particular current interest. Owing to vectorial electron flow across the thylakoid membrane, plastoquinone is thought to be reduced on the outside and plastohydroquinone to be oxidized on the inside of the membrane. This results in a proton translocation across the membrane and a build-up of a proton motive force which drives ATP formation. Old and new plastoquinone antagonists are described and the relevance of inhibitor studies on the rôle of plastoquinone in electron flow and photophosphorylation is discussed. Open questions and current problems of the mechanism of plastoquinone/plastoquinol transport across the membrane - and of proton translocation connected to it - relevant for the mechanism of energy conservation in photosynthesis, are pointed out.

The role of ligands in electron transport in nanocrystal solids

Nanoscale ◽  
2020 ◽  
Vol 12 (45) ◽  
pp. 23028-23035
Author(s):  
Artem R. Khabibullin ◽  
Alexander L. Efros ◽  
Steven C. Erwin
Keyword(s):  
Electron Transport ◽  
Theoretical Modeling

Theoretical modeling of wavefunction overlap in nanocrystal solids elucidates the important role played by ligands in electron transport.

scholarly journals Are Scientific Models of Life Testable? A Lesson from Simpson’s Paradox

Sci ◽  
2020 ◽  
Vol 2 (3) ◽  
pp. 73
Author(s):  
Prasanta S. Bandyopadhyay ◽  
Nolan Grunska ◽  
Don Dcruz ◽  
Mark C. Greenwood
Keyword(s):  
Origin Of Life ◽  
Rna World ◽  
Scientific Models ◽  
Scientific Model ◽  
Simpson’S Paradox ◽  
World Theory ◽  
Life Issues ◽  
The Origin Of Life ◽  
Logical Sense ◽  
Simpson's Paradox

We address the need for a model by considering two competing theories regarding the origin of life: (i) the Metabolism First theory and (ii) the RNA World theory. We discuss two inter-related points. (I) Models are valuable tools in understanding both the processes and intricacies of the origin of life issues. (II) Insights from models also help us to evaluate the core objection to origin of life theories called “the inefficiency objection” commonly raised by proponents of both the Metabolism First theory and the RNA World theory against each other. We use Simpson’s paradox as a tool for challenging this objection. We will use models in various senses ranging from taking them as representations of reality to treating them as theories/accounts that provide heuristics for probing reality. In this paper, we will frequently use models and theories interchangeably. Additionally, we investigate Conway’s Game of Life and contrast it with our Simpson’s Paradox (SP)-based approach to emergence of life issues. Finally, we discuss some of the consequences of our view. A scientific model is testable in three senses: (i) a logical sense, (ii) a nomological sense, and (iii) a current technological sense. The SP-based model is testable in the logical sense. It is also testable nomologically. However, it is not currently feasible to test it.

Sign in / Sign up

Export Citation Format

Share Document