A recent scientific article has stated that eukaryotes are positioned at the convergence of the “ring of life”. This statement was made after observing how eukaryotes interact with bacteria and archaea.
The term “eukaryote” refers to any organism whose genetic material is contained within a cell nucleus. This includes animals, plants, and fungi. Prokaryotes, which are organisms whose cells lack a cell nucleus, include bacteria and archaea.
How did the researchers make this conclusion? They used an extensive database of genetic information from different organisms to create a family tree linking all these organisms to each other. Then they analyzed which groups of organisms appeared in the same “nodes” or branches on the tree—that is, which groups had a common ancestor.
The researchers found that all three domains—bacteria, archaea, and eukaryotes—appeared in the same node some 2 billion years ago.
Eukaryotes are the largest cells
In addition to being the largest cells, eukaryotes also have a few other unique properties that set them apart from prokaryotes and other eukaryotic cells.
One of these properties is the presence of a double membrane surrounding the cell. The inner membrane is connected to the plasma membrane, which surrounds the entire cell. The outer membrane is connected to the cell wall, which surrounds the entire cell structure.
This double membrane system may be related to the evolutionary history of eukaryotic cells. It has been hypothesised that early eukaryotic cells may have been prokaryotic symbionts (a host cell inhabited by a smaller organism) that acquired a plasma membrane and a internalized nucleus containing genetic material.
This would explain why Eucarya is placed within Archaebacteria-eukaryotes because they share common features such as having a nucleus containing genetic material but lack other archaebacterial characteristics such as having an internal metabolism or an outer sheath covering the cell.
Eukaryotes have the most complex structures
All living things have a nucleus, but only eukaryotes have a complex nuclear structure. Prokaryotes do not have this intricate structure that controls genes.
Prokaryotes only have RNA (ribosomal or messenger) and DNA (genetic). Eukaryotes also have a third layer called the nucelar matrix. This is made of protein which helps organize the genetic material and structures that control gene expression.
This includes compartments called nucleoli, where ribosomes assemble to make proteins, and the kinetochore, which connects the chromosome to spindle fibers during cell division.
These additions make up the most complex nuclear structures among all life forms. The complexity of these structures supports the position of eukaryotes at the convergence of the “ring of life”.
Eukaryotic cells have internal membranes
A defining characteristic of the eukaryotic cell is the presence of internal membranes. These membranes create compartments within the cell where specific functions take place.
These compartments are called organelles, and they include the nucleus, endoplasmic reticulum (ER), golgi apparatus, lysosomes, vacuoles, and mitochondria.
The nucleus contains the genetic material in the form of DNA. The endoplasmic reticulum and golgi apparatus both play a role in protein production and distribution. Lysosomes contain digestive enzymes that break down materials in the cell. Vacuoles function to transport substances into the cell or expel them from the cell. Mitochondria produce energy for cellular processes using oxygen and glucose.
All of these organelles have been observed in prokaryotic cells as well. However, they are much smaller and lack internal membranes.
The eukaryotic cell contains a nucleus
Several other observations support the position of eukaryotes at the convergence of the “ring of life.” One such observation is the presence of a nucleus in eukaryotic cells.
Prokaryotic cells do not contain a nuclear membrane or a nuclear pores system. This feature is clearly observable with a microscope.
However, some protist cells do have anucleus that is often referred to as a nucleoid. The difference between these two structures is that the nucleoid does not contain DNA, whereas the anucleus does.
This distinction is important because it shows that even prokaryotic cells can have what appears to be a nucleus, but they lack essential features of the internal structure of a true nucleus.
The presence of these features in eukaryotic cells clearly demonstrates their divergence from prokaryotes and their inclusion in the domain Eukarya.
Eukaryotic cells contain mitochondria
The observation that eukaryotic cells contain mitochondria supports the theory that eukaryotes emerged at the convergence of the Bacteria-Archaea-Eubacteria-Eukaryota ring of life.
Mitochondria are organelles responsible for energy production in a cell. They have their own DNA, called mitochondrial DNA (mtDNA).
This is how scientists discovered mtDNA in the first place—they searched for signs of it in cells. They found it in all eukaryotic cells, which is why scientists now believe that all eukaryotes inherit their energy production systems from a common ancestor.
This is also why some scientists think that the acquisition of mitochondria was an important step in evolution—it enabled more complex cells to exist.
Indeed, many lower life forms do not have these organelles, making them simpler organisms.
Eukaryotic cells are found in plants and animals
Another point in favor of the eukaryotic cell being a chimera is that eukaryotic cells can contain prokaryotic cells. Prokaryotes are simple, single-celled organisms with no internal structure or membranebound nucleus.
Prokaryotic cells can be found inside the eukaryotic cells that make up plants and animals. These are known as intracellular parasites and are typically targeted by the immune system.
This evidence supports the idea that eukaryotes evolved from prokaryotes via symbiosis, not divergence. The two domains combined to form the new domain of Eukarya through this process.
The eukaryotic cell has a more complex organization
The eukaryotic cell contains several structures that are absent from prokaryotic cells. Among these structures are the nucleus, the cytoskeleton, and membrane-bound organelles.
The nucleus is a membrane-bound structure that encloses the genetic material of the cell in an aqueous environment. The cytoskeleton is made of proteins that function as a scaffold to organize and transport other cell components such as organelles and macromolecules.
Membrane-bound organelles such as the Golgi apparatus and lysosomes are also unique to eukaryotic cells. These contain specific compartments containing different materials that perform specific functions within the cell.
All of these features support the position of eukaryotes at the convergence of the “ring of life” due to their similarity to prokaryotic and archaea domains, but not in relation to bacteria.
Cells with nuclei can store more information about their environment and pass it on to the next generation
The ability to inherit information from the previous generation is a key feature of all life. This information is stored in the form of genes, which are sequences of instructions for building and maintaining an organism.
All life forms, from bacteria to plants and animals, have some sort of genetic information stored in their cells. This is why it’s often said that “DNA determines destiny.”
Genetic information is passed from one cell generation to the next via cell division. When a cell divides into two new cells, it passes on some of its genetic information to them. These new cells then go on to divide and develop into new cells or tissues in the organism.
Some types of bacteria do not have cell nuclei, so they do not have any genetic information stored in a nucleus. As a result, they cannot pass on any inherited traits to their offspring—only to their immediate descendants through cell division.
