Bookmarks

Interesting Links/bookmarks for personal use or sharing with others
Bookmarked Budding and Division of Giant Vesicles Linked to Phospholipid Production by Juan M. Castro, Hironori Sugiyama, Taro Toyota (Scientific Reports volume 9, Article number: 165 (2019))
The self-reproduction of supramolecular assemblies based on the synthesis and self-assembly of building blocks is a critical step towards the construction of chemical systems with autonomous, adaptive, and propagation properties. In this report, we demonstrate that giant vesicles can grow and produce daughter vesicles by synthesizing and incorporating phospholipids in situ from ad-hoc precursors. Our model involves acyl chain elongation via copper(I)-catalyzed azide-alkyne [3 + 2] cycloaddition reaction and the ensuing production of synthetic phospholipids to induce budding and division. In addition, the growth and budding of giant vesicles were compatible with the encapsulation and transfer of macromolecules as large as lambda phage DNA to the buds. This chemical system provides a useful model towards the implementation of cell-like compartments capable of propagation and transport of biological materials.

ᔥ Michael Marshall in He may have found the key to the origins of life. So why have so few heard of him? ()

Bookmarked The Emergence of Competition Between Model Protocells (science.sciencemag.org)
The transition from independent molecular entities to cellular structures with integrated behaviors was a crucial aspect of the origin of life. We show that simple physical principles can mediate a coordinated interaction between genome and compartment boundary, independent of any genomic functions beyond self-replication. RNA, encapsulated in fatty acid vesicles, exerts an osmotic pressure on the vesicle membrane that drives the uptake of additional membrane components, leading to membrane growth at the expense of relaxed vesicles, which shrink. Thus, more efficient RNA replication could cause faster cell growth, leading to the emergence of Darwinian evolution at the cellular level.
ᔥ Michael Marshall in He may have found the key to the origins of life. So why have so few heard of him? ()
Bookmarked Experimental Models of Primitive Cellular Compartments: Encapsulation, Growth, and Division (science.sciencemag.org)
The clay montmorillonite is known to catalyze the polymerization of RNA from activated ribonucleotides. Here we report that montmorillonite accelerates the spontaneous conversion of fatty acid micelles into vesicles. Clay particles often become encapsulated in these vesicles, thus providing a pathway for the prebiotic encapsulation of catalytically active surfaces within membrane vesicles. In addition, RNA adsorbed to clay can be encapsulated within vesicles. Once formed, such vesicles can grow by incorporating fatty acid supplied as micelles and can divide without dilution of their contents by extrusion through small pores. These processes mediate vesicle replication through cycles of growth and division. The formation, growth, and division of the earliest cells may have occurred in response to similar interactions with mineral particles and inputs of material and energy.
ᔥ Michael Marshall in He may have found the key to the origins of life. So why have so few heard of him? ()
Bookmarked Nonenzymatic Template-Directed RNA Synthesis Inside Model Protocells by Katarzyna Adamala (science.sciencemag.org)
The potential for self-replication makes RNA an attractive candidate as a primordial catalysis in the origin of life. Catalysis may have occurred in some kind of compartment, possibly a fatty acid vesicle. However, RNA catalysis generally requires high levels of magnesium, which are incompatible with fatty acid vesicle integrity. Adamala and Szostak (p. [1098][1]) screened magnesium chelators and found that several—including citrate, isocitrate, and oxalate—could maintain the membrane stability of fatty acid vesicles in the presence of Mg2+. Citrate also allowed Mg2+-dependent RNA synthesis within protocell-like vesicles, while at the same time protecting RNA from Mg2+-catalyzed degradation. Efforts to recreate a prebiotically plausible protocell, in which RNA replication occurs within a fatty acid vesicle, have been stalled by the destabilizing effect of Mg2+ on fatty acid membranes. Here we report that the presence of citrate protects fatty acid membranes from the disruptive effects of high Mg2+ ion concentrations while allowing RNA copying to proceed, while also protecting single-stranded RNA from Mg2+-catalyzed degradation. This combination of properties has allowed us to demonstrate the chemical copying of RNA templates inside fatty acid vesicles, which in turn allows for an increase in copying efficiency by bathing the vesicles in a continuously refreshed solution of activated nucleotides. [1]: /lookup/doi/10.1126/science.1241888

ᔥ Michael Marshall in He may have found the key to the origins of life. So why have so few heard of him? ()

Bookmarked Origin of life: The RNA world by Walter Gilbert (Nature volume 319, page618 (1986))
UNTIL recently, when one thought of the varied molecular processes at the origin of life, one imagined that the first self-replicating systems consisted of both RNA and protein. RNA served to hold information, whereas protein molecules provided all the enzymic activities needed to make copies of RNA and to reproduce themselves. The cycle that developed a self-replicating system out of the primitive soup of amino acids and nucleotides had two radically different components.

ᔥ Michael Marshall in He may have found the key to the origins of life. So why have so few heard of him? ()

Bookmarked The Best Black History Books of 2020 (AAIHS)
We asked editors and bloggers of Black Perspectives to select the best books published in 2020 on Black History, and they delivered! Check out this extraordinary list of great books from 2020 that offer varied historical perspectives on the Black experience in the United States and across the globe.
A good looking list. I’ve already got a few in my pile for the new year.
Bookmarked The ergodicity problem in economics by Ole Peters (Nature Physics volume 15, pages1216–1221(2019))
The ergodic hypothesis is a key analytical device of equilibrium statistical mechanics. It underlies the assumption that the time average and the expectation value of an observable are the same. Where it is valid, dynamical descriptions can often be replaced with much simpler probabilistic ones — time is essentially eliminated from the models. The conditions for validity are restrictive, even more so for non-equilibrium systems. Economics typically deals with systems far from equilibrium — specifically with models of growth. It may therefore come as a surprise to learn that the prevailing formulations of economic theory — expected utility theory and its descendants — make an indiscriminate assumption of ergodicity. This is largely because foundational concepts to do with risk and randomness originated in seventeenth-century economics, predating by some 200 years the concept of ergodicity, which arose in nineteenth-century physics. In this Perspective, I argue that by carefully addressing the question of ergodicity, many puzzles besetting the current economic formalism are resolved in a natural and empirically testable way.
↬ Kevin Marks retweet () of 
↬ Simon Wardley @swardley in Simon Wardley on Twitter: “Anyway, this is a fabulous paper – The ergodicity problem in economics – https://t.co/fzS3toWvT5 … well worth the read.” / Twitter ()