Two mitochondria from mammalian lung tissue displaying their matrix and membranes as shown by electron microscopy
Four Scientists from Goethe University, Frankfurt, Germany have shown just how fully mitochondria have integrated into their endosymbiotic host cells over the course of their evolutionary history.
First a little background from ChatGPT3:
Mitochondria and how they evolved>The scientists' findings are explained in a Goethe University press release:
Mitochondria are double-membraned organelles found in the cells of most eukaryotic organisms, including plants, animals, fungi, and protists. They play a crucial role in cellular respiration, where they generate adenosine triphosphate (ATP), the primary energy currency of cells. Mitochondria are believed to have evolved from endosymbiosis, a process where one organism lives within another and both organisms benefit from the relationship.
The endosymbiotic theory suggests that mitochondria originated from a free-living bacterium that was engulfed by an ancient eukaryotic cell. Over time, the bacterium and the host cell developed a symbiotic relationship, where the bacterium provided energy through respiration, and the host cell provided protection and nutrients. Eventually, the bacterium lost some of its independence and became a specialized organelle within the host cell – the mitochondrion.
Evidence supporting the endosymbiotic theory of mitochondria includes:Further Reading:
- Similarities in DNA: Mitochondria have their own DNA, known as mitochondrial DNA (mtDNA). This DNA is circular, like bacterial DNA, and is separate from the cell's nuclear DNA. The presence of mtDNA supports the idea that mitochondria have a bacterial origin.
- Replication: Mitochondria have their own machinery for replication, similar to bacteria. They can divide independently within the cell, a process similar to bacterial binary fission.
- Size and Shape: Mitochondria are similar in size and shape to certain bacteria. They are also similar to bacteria in terms of their inner structure and composition of membranes.
- Endosymbiotic Relationships in Nature: Similar endosymbiotic relationships can be observed in modern organisms. For example, some bacteria live inside the cells of certain insects, providing essential nutrients to their host.
Remember that the field of evolutionary biology is constantly evolving, and new research and findings may have emerged beyond my last update in September 2021. Always check for the latest literature and credible sources for up-to-date information on any scientific topic.
- Margulis, L. (1970). Origin of Eukaryotic Cells. Yale University Press.
This book by Lynn Margulis is a classic work that delves into the endosymbiotic theory and the origins of eukaryotic cells, including the evolution of mitochondria.- Gray, M. W. (2012). Mitochondrial evolution. Cold Spring Harbor Perspectives in Biology, 4(9), a011403.
This paper provides a comprehensive overview of mitochondrial evolution and the evidence supporting the endosymbiotic theory.- Lane, N. (2015). Bioenergetic Constraints on the Evolution of Complex Life. Cold Spring Harbor Perspectives in Biology, 6(5), a015982.
This article discusses the role of mitochondria in the evolution of complex life and how their symbiotic relationship with eukaryotic cells was critical for the development of multicellular organisms.- Sagan, L. (1967). On the origin of mitosing cells. Journal of Theoretical Biology, 14, 255-274.
This is an early paper on the endosymbiotic theory of mitochondria, written by Lynn Margulis under her previous name Lynn Sagan. It provides an essential historical perspective on the topic.
ChatGPT3 "Tell me all about mitochondria and how they evolved, with references for further reading." [Response to user request]
Retrieved from https://chat.openai.com/
Originally, the powerhouses of higher cells, the mitochondria, were independent organisms. Researchers at Goethe University Frankfurt have investigated to what extent their metabolism has blended with that of their host cells in the course of evolution, using the example of a mitochondrial stress response. They have discovered that mitochondria send two different biochemical signals. These are processed together in the cell and trigger a support mechanism to restore cellular balance (homeostasis). The work was partly done within the ENABLE cluster initiative (now EMTHERA) at Goethe University Frankfurt.The team's findings are published, open access, in Nature:
As life propagated across Earth in the form of the widest variety of single-celled organisms, sometime between 3.5 and a billion years ago one such organism managed an evolutionary coup: Instead of devouring and digesting bacteria, it encapsulated its prey and used it as a source of energy. As a host cell, it offered protection and nutrition in return. This is referred to as the endosymbiotic theory, according to which that single-celled organism was the primordial mother of all higher cells, out of which all animals, fungi and plants developed. Over the course of billions of years, the encapsulated bacterium became the cell’s powerhouse, the mitochondrion, which supplies it with the cellular energy currency ATP. It lost a large part of its genetic material – its DNA – and exchanged smaller DNA segments with the mother cell. However, now as in the past, mitochondria divide independently of the cell and possess some genes of their own.
How closely the cell and the mitochondrion work together in human cells today is what a team of researchers led by Dr. Christian Münch of Goethe University Frankfurt is investigating. They have now discovered how the mitochondrion calls for help from the cell when it is under stress. Triggers for such stress can be infections, inflammatory diseases or genetic disorders, for example, but also nutrient deficiencies or cell toxins.
A certain type of mitochondrial stress is caused by misfolded proteins that are not quickly degraded and accumulate in the mitochondrion. The consequences for both the mitochondrion and the cell are dramatic: Misfolded proteins can, for example, disrupt energy production or lead to the formation of larger amounts of reactive oxygen compounds, which attack the mitochondrial DNA and generate further misfolded proteins. In addition, misfolded proteins can destabilize the mitochondrial membranes, releasing signal substances from the mitochondrion that activate apoptosis, the cell’s self-destruction program.
The mitochondrion responds to the stress by producing more chaperones (folding assistants) to fold the proteins in order to reduce the misfolding, as well as protein shredding units that degrade the misfolded proteins. Until now, how cells trigger this protective mechanism was unknown.
The researchers from Goethe University Frankfurt artificially triggered misfolding stress in the mitochondria of cultured human cells and analyzed the result. “What makes it difficult to unravel such signaling processes,” explains Münch, himself a biochemist, “is that an incredibly large number take place simultaneously and at high speed in the cell.” The research team therefore availed itself of methods (transcriptome analyses) that can be used to measure over time to what extent genes are transcribed. In addition, the researchers observed, among other things, which proteins bind to each other at which point in time, at which intervals the concentrations of intracellular substances change, and what effects there are when individual proteins are systematically deactivated.
The result is that the mitochondria send two chemical signals to the cell when protein misfolding stress occurs: They release reactive oxygen compounds and block the import of protein precursors, which are produced in the cell and are only folded into their functional shape inside the mitochondrion, causing these precursors to accumulate in the cell. Among other things, the reactive oxygen compounds lead to chemical changes in a protein called DNAJA1. Normally, DNAJA1 supports a specific chaperone (folding assistant) in the cell, which molds the cell’s newly formed proteins into the correct shape.It was very exciting to discover how the two mitochondrial stress signals are combined into one signal in the cell, which then triggers the cell’s response to mitochondrial stress. Moreover, in this complex process, which is essentially driven by tiny local changes in concentration, the stress signaling pathways of the cell and the mitochondrion dovetail very elegantly with each other – like the cogs in a clockwork.
Christian Münch, Corresponding author
Institute of Biochemistry II
Faculty of Medicine
Goethe University Frankfurt, Frankfurt am Main, Germany
As a consequence of the chemical change, DNAJA1 now increasingly forces itself on the folding assistant HSP70 as its helper. HSP70 then takes special care of the misfolded protein precursors that accumulate around the mitochondrion because of the blocked protein import. By doing so, HSP70 reduces its interaction with its regular partner HSF1. HSF1 is now released and can migrate into the cell nucleus, where it can trigger the anti-stress mechanism for the mitochondrion.
AbstractWhat's happened here then is that the endosymbiotic bacteria that evolved into the mitochondria of eukaryote cells have lost most of their original DNA which has migrated to the host cell nucleus, so when they need the enzymes that repair errors in the folding of their proteins, they need to signal that to the host cell.
The mitochondrial unfolded protein response (UPRmt) is essential to safeguard mitochondria from proteotoxic damage by activating a dedicated transcriptional response in the nucleus to restore proteostasis1,2. Yet, it remains unclear how the information on mitochondria misfolding stress (MMS) is signalled to the nucleus as part of the human UPRmt (refs. 3,4). Here, we show that UPRmt signalling is driven by the release of two individual signals in the cytosol—mitochondrial reactive oxygen species (mtROS) and accumulation of mitochondrial protein precursors in the cytosol (c-mtProt). Combining proteomics and genetic approaches, we identified that MMS causes the release of mtROS into the cytosol. In parallel, MMS leads to mitochondrial protein import defects causing c-mtProt accumulation. Both signals integrate to activate the UPRmt; released mtROS oxidize the cytosolic HSP40 protein DNAJA1, which leads to enhanced recruitment of cytosolic HSP70 to c-mtProt. Consequently, HSP70 releases HSF1, which translocates to the nucleus and activates transcription of UPRmt genes. Together, we identify a highly controlled cytosolic surveillance mechanism that integrates independent mitochondrial stress signals to initiate the UPRmt. These observations reveal a link between mitochondrial and cytosolic proteostasis and provide molecular insight into UPRmt signalling in human cells.
Sutandy, F.X.R., Gößner, I., Tascher, G. et al.
A cytosolic surveillance mechanism activates the mitochondrial UPR.
Nature 618, 849–854 (2023). https://doi.org/10.1038/s41586-023-06142-0
Copyright: © [year] The authors.
Published by [publisher]. Open access
Reprinted under a Creative Commons Attribution 4.0 International license (CC BY 4.0)
This illustrates just how fully the mitochondria have integrated into the original host (probably an arcae) through the process of evolution over between 1 and 3 billion years.
What doesn't make any sense at all from an intelligent [sic] design point of view is why the mitochondria need this complex system when they could have been designed to retain the genes needed, even if the designer was so incompetent as to design them so they have errors in their protein folding that need to be repaired, in the first place.
The answer is that they are not the result of intelligent design but of the sub-optimal result of utilitarian evolution, which has no ability to plan and no ability to scrap a bad design and start again. The result is a complex work-around to improve an inefficient, evolved process.
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