Lynn Margulis Dies
23/11/11 13:33 Filed in: GenomeWeb Daily Scan
Submitted by S. Pelech - Kinexus on Thu, 11/24/2011 - 13:33.
Lynn Margulis' endosymbiotic theory was one of the most memorable concepts that fascinated me as an undergraduate student in the 1970's. Gene sequencing studies since then have lent strong support in favour of the hypothesis that the mitochondria and chloroplasts in eukaryotic cells have bacterial origins.
In a typical mammal cell, such as a hepatocyte, there may be as many as 2000 mitochondria per cell, each undergoing reproduction by fission. However, some types of cells exist that may have a single mitochondrion. At least 37 gene are found in the human mitochondrial genome, most of which encode mitochondrial tRNA and respiratory proteins. Around a quarter of the total mRNA in a typical cell may arise from transcription of the mitochondrial genes, despite the co-presence of about 23,000 nuclear genes. It appears that there is variation in the precise nucleotide sequences of mitochondrial genes in the same cell, so in a sense, the mitochondria are a heterogeneous colony of independently replicating symbiotic parasites. The ubiquitous presence of mitochondria in eukaryotic cells indicates that they are fundamental to origin of eukaryotic cells. Moreover, their ability to metabolize oxygen, which was toxin to many bacteria in early life on this planet, probably played a major role in forging the endosymbiotic relationship found in eukaryotes. Through oxidative phosphorylation, mitochondria produce ATP, which fuels most of the metabolic reactions in eukaryotic cells. Significantly, any damage to even a few mitochondria that results in the leakage of certain mitochondrial proteins (e.g. cytochrome C) will trigger the suicide of the entire cell. This ensures that if the mitochondria are adversely affected, the entire cell will go down too.
It seems that the fundamental role of endosymbiotic relationships in complex life forms has even been picked up in many popular science fiction creations. It clearly inspired George Lucas to write in his Star Wars saga about the "Force" that is created by microorganisms found within all living cells that he called "midi-chlorians". May your mitochondria live long and your ATP levels always stay high!
Link to the original blog post.
Lynn Margulis' endosymbiotic theory was one of the most memorable concepts that fascinated me as an undergraduate student in the 1970's. Gene sequencing studies since then have lent strong support in favour of the hypothesis that the mitochondria and chloroplasts in eukaryotic cells have bacterial origins.
In a typical mammal cell, such as a hepatocyte, there may be as many as 2000 mitochondria per cell, each undergoing reproduction by fission. However, some types of cells exist that may have a single mitochondrion. At least 37 gene are found in the human mitochondrial genome, most of which encode mitochondrial tRNA and respiratory proteins. Around a quarter of the total mRNA in a typical cell may arise from transcription of the mitochondrial genes, despite the co-presence of about 23,000 nuclear genes. It appears that there is variation in the precise nucleotide sequences of mitochondrial genes in the same cell, so in a sense, the mitochondria are a heterogeneous colony of independently replicating symbiotic parasites. The ubiquitous presence of mitochondria in eukaryotic cells indicates that they are fundamental to origin of eukaryotic cells. Moreover, their ability to metabolize oxygen, which was toxin to many bacteria in early life on this planet, probably played a major role in forging the endosymbiotic relationship found in eukaryotes. Through oxidative phosphorylation, mitochondria produce ATP, which fuels most of the metabolic reactions in eukaryotic cells. Significantly, any damage to even a few mitochondria that results in the leakage of certain mitochondrial proteins (e.g. cytochrome C) will trigger the suicide of the entire cell. This ensures that if the mitochondria are adversely affected, the entire cell will go down too.
It seems that the fundamental role of endosymbiotic relationships in complex life forms has even been picked up in many popular science fiction creations. It clearly inspired George Lucas to write in his Star Wars saga about the "Force" that is created by microorganisms found within all living cells that he called "midi-chlorians". May your mitochondria live long and your ATP levels always stay high!
Link to the original blog post.