What was the first cells

Fossil evidence shows that multicellular life came into existence about million years ago, however, the age of the earth was over 4. Putting these two facts together, it seemed that the earth was lifeless for its first 3 billion years, and during that time the constituents of the first cells were slowly synthesized, drawn together and assembled into the first proto-cell.

However, once the first cell had been formed, well understood evolutionary forces took over and very quickly multicellular creatures appeared, adapted to a wide variety of environmental condition and rapidly spread out over the surface of the planet. But this conventional view appears to be wrong. In E. The emergence of peptides promoting its replication opened up the world of RNA genomes, where transcription of RNA and replication A process for obtaining two molecules identical to the original molecule.

A transcription process produced templates for decoding the message by the protoribosome, while replication increased the number of copies of this RNA ancestor of genes. This step led to the formation of vesicles containing sets of various sequences of RNA double helices, as found in the genome of some RNA viruses today. However, these protocells depended on the ongoing synthesis of ribonucleotides and polyribonucleotides, which are chemically very unstable molecules.

This continuous process required the association within the same compartment a primitive cell of both the reproduction of the RNA-metabolism world and the specific replication of the RNA-genome world. The RNA-genome world had therefore to find a way to stabilize the synthesis of its precursors so as not to be doomned to disappear.

The discovery of deoxyribose, much more stable than ribose, resolved this quandary. Thus, DNA, a molecule very stable over time, appeared only at the very end of the process that resulted in memorizing the recipes that drive the production of metabolism. This novel molecule kept memory apart from general functioning of the cell. This final stage witnesses the moment when the first cells were born. To understand their emergence, it is necessary to explore how vesicles surrounded by a lipid bilayer interact.

They can split and merge, but a constant property is their ability to interpenetrate, as observed today in the process of phagocytosis Process allowing a cell to encompass and then digest a foreign substance or organism e. This process considerably enriches the evolution of metabolic systems since it allows the association in a single cell of compartments with different but complementary destinies. The ancestor of the first cells was a phagocyte, associating an RNA-metabolism -ancestor of the cytoplasm Internal cell environment.

It consists of a water- and protein-rich phase cytosol and contains cellular organelles mitochondria, etc. At this point of evolution, we are therefore faced with a set of phagocytes, the protokaryotes , which evolve by reproducing and systematically ingesting what surrounds them.

They are fairly large cannibal predators like protists today , producing metabolic innovations that they consume and propagate. This situation is unstable. Indeed, it brings out a specific function, the one that allows resistance to phagocytosis. If an organism with a flexible metabolism finds a structure that can carry out this resistance, it will escape the cannibalism of protokaryotic organisms and start a new evolutionary lineage.

Two solutions to this barrier are possible: surround the cell with an envelope that is very difficult to ingest, or make phagocytosis impossible for physico-chemical reasons. Bacteria are the descendants of the cells that have found the first solution, forming small cells and surrounded by a resistant envelope. Archaea are those which have discovered how to surround themselves with a membrane that is impossible to ingest as a functional structure, using lipids with a three-dimensional structure that mirrors the lipids of their predators.

They further escaped by colonizing extreme environments Figure 4. To sum up, the emergence of stable deoxyribonucleotides has allowed the grouping of genes within chromosomes, while phagocytosis has led to an escape process based on a metabolic alternative to the structure of membrane lipids and the conquest of extreme environments, with Archaea Single-celled prokaryotic microorganisms living in particular in extreme environments anaerobic, highly saline, very hot….

Phylogenetic research by Carl Woese and George E. Fox differentiated between archaea and other prokaryotic organisms bacteria. Currently, living organisms are considered to consist of three groups: archaea, bacteria and eukaryotes. Then, as Bacteria and Archaea miniaturized the cell, some Bacteria regained an interest in sharing metabolism, simplifying their envelope so that some of them became symbionts of protokaryotes in a way reminiscent of the way some bacteria form nodules in plant roots.

The pursuit of a reductive evolution transformed this symbiosis to the point of reducing the bacterial genome to a small set of genes, within mitochondria , organelles specific to eukaryotes Unicellular or multicellular organisms whose cells possess a nucleus and organelles endoplasmic reticulum, Golgi apparatus, various plasters, mitochondria, etc.

Eukaryotes are, along with bacteria and archaea, one of the three groups of living organisms. Note that this scenario could possibly be validated experimentally.

This would be the case if somewhere there was still a direct descendant of the protokaryotes. This hypothetical organism would have the particularity of having a cytoplasm and a nucleus, but no mitochondria nor traces of organelles of bacterial origin. Since the main function of mitochondria today is the formation of iron-sulfur clusters essential for the activity of many enzymes, these organisms must be sought in environments where access to these structures is easy.

If such an organization existed, it would be a considerable asset to transform the present scenario from an educated guess into a scientific reality. In summary, the proposed scenario of origins Figure 5 assumes that individuals of the same species are all different from one another. However, it also assumes that it is a common program that decides on their construction. This program is transmitted from generation to generation, unmodified it replicates , while individual cells only reproduce they are similar, not identical, to one another.

This distinction between reproduction and replication is essential to understand what life is, a dialogue between the inevitable production of variants , and the maintenance over generations of a program that is as invariant as possible. Cover image. Second edition ISBN These have important functions in decomposing different types of materials, such as bacteria and parts of cells that have worn out.

The earliest protocells may have been elusive entities, though, often dissolving and reforming as they circulated within the vents. The evolution of an enzyme called pyrophosphatase, which catalyses the production of pyrophosphate, allowed the protocells to extract more energy from the gradient between the alkaline vent fluid and the acidic ocean.

This ancient enzyme is still found in many bacteria and archaea , the first two branches on the tree of life. Some protocells started using ATP as well as acetyl phosphate and pyrophosphate. The production of ATP using energy from the electrochemical gradient is perfected with the evolution of the enzyme ATP synthase , found within all life today.

Protocells further from the main vent axis, where the natural electrochemical gradient is weaker, started to generate their own gradient by pumping protons across their membranes, using the energy released when carbon dioxide reacts with hydrogen. Oxygen was toxic to most early cells because they had evolved in its absence.

As a result, many of them died out. The few that survived evolved a new way to take advantage of the oxygen. This second major innovation was cellular respiration.

It allowed cells to use oxygen to obtain more energy from organic molecules. The First Cells What was needed for the first cell? LUCA No doubt there were many early cells of this type. Photosynthesis and Cellular Respiration The earliest cells were probably heterotrophs. Summary The first cells consisted of little more than an organic molecule such as RNA inside a lipid membrane.

One cell or group of cells , called the last universal common ancestor LUCA , gave rise to all subsequent life on Earth.

Photosynthesis evolved by 3 billion years ago and released oxygen into the atmosphere. Cellular respiration evolved after that to make use of the oxygen. Explore More Use the time slider in this resource to answer the questions that follow.