Membrane Transport in Primitive Cells

Mansy, Sheref S.

doi:10.1101/cshperspect.a002188

Cited by 103 publications

(107 citation statements)

References 79 publications

(92 reference statements)

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“…Lipid bilayers are notoriously leaky to protons (Nichols and Deamer 1980;Paula et al 1996), so the first self-assembled membranes composed of relatively short-chain amphiphiles would be unable to maintain significant proton gradients, as recently shown by Chen and Szostak (2004). Mansy (2010) discusses the role of membrane permeability in primitive cellular systems. Even if a plausible primitive barrier membrane can be discovered, an electron transport system and ATP synthase would need to be incorporated in the bilayer for chemiosmosis to be a source of chemical energy.…”

Section: Chemiosmotic Energy Conversion To Anhydride Energymentioning

confidence: 95%

Bioenergetics and Life's Origins

Deamer¹,

Weber²

2010

Cold Spring Harbor Perspectives in Biology

149

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Bioenergetics is central to our understanding of living systems, yet has attracted relatively little attention in origins of life research. This article focuses on energy resources available to drive primitive metabolism and the synthesis of polymers that could be incorporated into molecular systems having properties associated with the living state. The compartmented systems are referred to as protocells, each different from all the rest and representing a kind of natural experiment. The origin of life was marked when a rare few protocells happened to have the ability to capture energy from the environment to initiate catalyzed heterotrophic growth directed by heritable genetic information in the polymers. This article examines potential sources of energy available to protocells, and mechanisms by which the energy could be used to drive polymer synthesis.P revious research on life's origins has for the most part focused on the chemistry and energy sources required to produce the small molecules of life-amino acids, nucleobases, and amphiphiles-and to a lesser extent on condensation reactions by which the monomers can be linked into biologically relevant polymers. In modern living cells, polymers are synthesized from activated monomers such as the nucleoside triphosphates used by DNA and RNA polymerases, and the tRNA-amino acyl conjugates that supply ribosomes with activated amino acids. Activated monomers are essential because polymerization reactions occur in an aqueous medium and are therefore energetically uphill in the absence of activation.A central problem therefore concerns mechanisms by which prebiotic monomers could have been activated to assemble into polymers. Most biopolymers of life are synthesized when the equivalent of a water molecule is removed to form the ester bonds of nucleic acids, glycoside bonds of polysaccharides, and peptide bonds in proteins. In life today, the removal of water is performed upstream of the actual bond formation. This process involves the energetically downhill transfer of electrons, which is coupled to either substrate-level oxidation or generation of a proton gradient that in turn is the energy source for the synthesis of anhydride pyrophosphate bonds in ATP. The energy stored in the pyrophosphate bond is then distributed throughout the cell to drive most other energydependent reactions. This is a complex and highly evolved process, so here we consider simpler ways in which energy could have been

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Section: Chemiosmotic Energy Conversion To Anhydride Energymentioning

confidence: 95%

Bioenergetics and Life's Origins

Deamer¹,

Weber²

2010

Cold Spring Harbor Perspectives in Biology

149

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“…All these processes have very acute requirements to be efficient: firstly, a membrane that is impermeable to protons, secondly, a series of membrane proteins capable of coupling electron transfers to proton translocations, and finally, membrane ATPsynthase that is by itself a very complex cellular machine [45]. Performing only one of these tasks would hardly be achievable by an emerging living organism, which raises a series of unanswered questions: -How could an impermeable membrane be formed whereas fatty acid-made membranes are notoriously leaky [46], except in the absence of alkali-metal cations or other permeable cations [47]? -How could the free energy from several events, each involving the translocation of a proton through the membrane, be harvested to build an ATP molecule from ADP and inorganic phosphate without a highly evolved molecular machine?…”

Section: (D) Adenosine Triphosphate and Chemiosmosismentioning

confidence: 99%

Energy flows, metabolism and translation

Pascal

Boiteau

2011

Phil. Trans. R. Soc. B

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Thermodynamics provides an essential approach to understanding how living organisms survive in an organized state despite the second law. Exchanges with the environment constantly produce large amounts of entropy compensating for their own organized state. In addition to this constraint on self-organization, the free energy delivered to the system, in terms of potential, is essential to understand how a complex chemistry based on carbon has emerged. Accordingly, the amount of free energy brought about through discrete events must reach the strength needed to induce chemical changes in which covalent bonds are reorganized. The consequence of this constraint was scrutinized in relation to both the development of a carbon metabolism and that of translation. Amino acyl adenylates involved as aminoacylation intermediates of the latter process reach one of the higher free energy levels found in biochemistry, which may be informative on the range in which energy was exchanged in essential early biochemical processes. The consistency of this range with the amount of energy needed to weaken covalent bonds involving carbon may not be accidental but the consequence of the abovementioned thermodynamic constraints. This could be useful in building scenarios for the emergence and early development of translation.

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“…Microspheres are bubbles that form spontaneously under primitive conditions [23]. A macromolecular polymer replication system could be encapsulated within a lipid membrane-bounded bubble and, while DNA transfer by conjugation is known as a common mechanism, naked gene transfers seem to occur very rarely under natural conditions [24][25][26]. According to aggregation logic, these primitive bubbles gathered and started exchanging materials.…”

Section: The Libertine Bubblesmentioning

confidence: 98%

“…The selective porosity of proto-cell membranes in contact with other proto-cell bubbles would be selected as long as the process allows the exchange and possible replication of compatible genetic material [26]. These exchanges presumably result in an increasing imbalance in the genetic content among bubbles, with some bubbles losing many genes while others develop an excess.…”

Section: The Libertine Bubblesmentioning

confidence: 99%