German biologists have experimentally proved that transport RNA molecules could become the main element in the evolution of early life forms. Under certain conditions, they are able to assemble into functional units that reproduce genetic information exponentially.
The transfer of genetic information is carried out sequentially: first from DNA to RNA (this process is called transcription), and then protein synthesis (translation) is realized on the RNA matrix. In an operation known as replication, proteins duplicate genetic information encoded in DNA molecules and stored in the cell nucleus, distribute it equally between two daughter cells during division, and the process repeats.
The paradox of the central dogma of molecular biology is that already at the first stage, complex protein compounds – enzymes act as transcription catalysts: in a certain section, the DNA double helix is unwound under the action of enzymes, and one of the chains becomes a matrix for building the so-called matrix, or informational RNA (mRNA), which then participates in translation.
That is, at the molecular level, the age—old question arises about the origin of life – what was primary – an egg or a chicken: proteins are necessary for the transmission of genetic information, but their synthesis itself depends on transcription.
Biologists from the Ludwig and Maximilian University of Munich have experimentally proved for the first time that small changes in transport RNA (tRNA) molecules allow them to assemble themselves into a functional unit that can reproduce information.
Thus, according to scientists, transport RNA acting as an intermediary between mRNA and proteins could be a key element in the evolution of early life forms: tRNA molecules could autonomously interact with each other to form a kind of replication module capable of exponentially replicating information.
"Our studies of early forms of molecular replication and our discovery of the link between replication and translation bring us closer to reconstructing the origin of life," one of the authors of the study, Dieter Braun, is quoted in a university press release.
In order for such a system to work, a non-equilibrium environment is needed to launch the corresponding physical and chemical processes, scientists believe. Therefore, all their experiments involved a repeating sequence of temperature fluctuations.
Each experiment started with a template – an information structure consisting of two types of central nucleotide sequences. The researchers demonstrated that under periodically changing conditions, a template binary structure can be copied repeatedly. Such a replication mechanism could have taken place in a hydrothermal microsystem on early Earth.
In particular, according to the authors, a favorable environment for such reaction cycles could have developed in porous rocks on the seabed, where natural temperature fluctuations are associated with convection currents.
Paleontologists have discovered sponge-like fossils in ancient reefs that are 890 million years old. If the results are confirmed, it will be the oldest find of multicellular living organisms on Earth.
It is believed that the first multicellular organisms, which can be confidently attributed to animals, appeared on Earth about 635 million years ago, in Ediacaria – the last geological period of the Proterozoic. We are talking about vendobionts – mysterious radially and bilaterally symmetrical organisms that led a sedentary or sedentary lifestyle.
However, some scientists believe that the first animals on Earth were sponges – marine multicellular attached to the bottom, which are still widely distributed around the world.
Well—preserved ancient fossil sponges have been known since the Cambrian period, which began 541 million years ago, but phylogenetic analysis and biomarkers indicate that sponges existed much earlier, and in sedimentary rocks aged 750 million years, scientists found silicon spicules – elements of the mineralized skeleton of sponges.
Canadian paleontologist Elizabeth Turner from Laurentian University has discovered fossils extremely similar in structure to sponges in ancient reefs in northwestern Canada. The reefs belong to bacterial structures, are composed of calcium carbonate and are 890 million years old.
In the rock samples, Turner identified branched networks of tubular structures mineralized with calcite – crystalline calcium carbonate. The researcher noted that these structures closely resemble the fibrous skeleton of horny sponges, which are currently used for the production of sponges for washing.
The author believes that these structures may be the fossilized remains of horn sponges that lived on carbonate reefs for another 90 million years before the oxygen level on Earth rose to concentrations that are considered necessary to maintain animal life.
If the scientist's assumptions are confirmed, it will turn out that the evolution of early animals on our planet occurred independently of oxygenation – oxygen saturation of the atmosphere, and the very first organisms were able to survive the most severe global glaciations of the cryogenic period in the history of the Earth, which occurred between 720 and 635 million years ago.
Judging by the results of micropetrographic reconstruction, the oldest sponge was an attached worm-like organism with a size from the first millimeters to a centimeter, which lived on the surface or inside reefs built by calcifying cyanobacteria-photosynthesizers.
The rarity of the finds of sponges of Neoproterozoic age is explained by the fact that, most likely, they did not have mineralized skeletons – siliceous or calcareous, but consisted exclusively of protein – spongin or keratin compounds. Therefore, the scientist believes, in ancient deposits it is necessary to look not for skeletal elements – spicules – but for prints of soft tissues that have preserved the structure. Paleontologists have met such structures before, but interpreted them as fossil colonies of algae or protozoa.