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Evolution of Organelles: Uncovering a New Case of Endosymbiosis
The intricate cells that form the foundation of animals and plants house various organelles, which are specialized compartments enclosed by membranes that carry out specific functions. Among these organelles, two crucial ones have emerged through a process known as endosymbiosis, where a previously independent organism is engulfed by a cell. These significant organelles are the mitochondrion, which originated from a bacterial entity and now manages the conversion of chemical energy into usable forms, and the chloroplast, where photosynthesis occurs.
While instances of organelles evolving via endosymbiosis are relatively rare, researchers have recently uncovered a potential new case. This discovery involves the evolution of an organelle dedicated to extracting nitrogen from the atmosphere, termed a nitroplast, as it undergoes the process of specialization.
Acquiring Nitrogen
Nitrogen holds a critical role in the realm of life, with every DNA base and amino acid containing at least one nitrogen atom. Yet, procuring nitrogen poses a significant challenge for living organisms. Although N2 molecules are abundant in the atmosphere, they are notoriously tough to split. Only bacteria possess the necessary enzymes, called nitrogenases, that can break down nitrogen, with the catch that they cease functioning in oxygen-rich environments. Consequently, many organisms must obtain nitrogen from external sources, contributing to the extensive energy expenditure involved in the production of nitrogen fertilizers for numerous crops.
Some plants, such as legumes, have devised a unique means of garnering nitrogen through a symbiotic relationship with bacteria. These plants develop specialized nodules that serve as a habitat for nitrogen-producing bacteria. This mutualistic bond exemplifies endosymbiosis, where microorganisms dwell inside an organism’s cells or body, exchanging essential substances for each other’s survival.
In more extreme scenarios, endosymbiosis escalates to become obligatory, with both organisms reliant on one another for survival. In certain insects, endosymbionts are transmitted to offspring during egg production, often lacking critical genes necessary for independent living. Nevertheless, such circumstances pale in comparison to the intricate integration witnessed in mitochondria and chloroplasts. These organelles undergo duplication and distribution during cell division, boasting minimal genomes and relying on the cell to produce most of their proteins, which are then imported into the organelles. This level of integration signifies the culmination of over a billion years of evolution since the inception of the endosymbiotic relationship.
Given the apparent scarcity of endosymbiotic occurrences beyond mitochondria and chloroplasts, the identification of a potential new example unveils a promising horizon for researchers. With only one confirmed instance of a recent endosymbiosis between eukaryotes and a bacterial species besides the known cases of eukaryotic algae incorporation in other eukaryotes, the discovery of an evolving nitroplast represents a compelling avenue for further exploration.
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