Read Online Creation by Adam Rutherford - Free Book Online Page B
Authors: Adam Rutherford
Ads: Link
with
G
and
A
pairs with
U
. But
C
and
G
form a bond that is more stable at higher temperatures. Therefore, we can infer from the relative amount of
CG
bonds in ribosomes a preference for warmer conditions. This is borne out across many species, and the ribosome in which we see the highest
CG
content are from high-temperature extremophilesâin other words, organisms that thrive in heat. Where do we find such creatures? In many places, but the most impressive habitat is in and around hydrothermal vents under the sea. There, heated by a rip in the earthâs surface, plumes of noxious chemicals that can boil the sea chug out. But dozens of species thrive there: bacteria, archaea, and even large, complex creatures such as the Pompeii worm, which can endure temperatures up to eighty degrees Celsius, more than 170 degrees Fahrenheit (not least because it wears an insulating fleece of hardy bacteria).
Some models of Lucaâs ribosomes suggest that the amount of
C
s and
G
s was disproportionately high in their component parts. This might suggest a hot home for the base of life. Certainly, the discovery of extremely heat-loving (aka hyperthermophilic) archaea and bacteria in such environments as the hot springs in Yellowstone Park or submarine thermal vents supports this idea, as these organisms mostly occupy spaces at the base of evolutionary trees, as much as we can reconstruct them.
But the simple truth is we donâtâand possibly canâtâknow. Reconstructing the past using phylogenetics is a complicated art, with many confounding factors. Using the ever-changing DNA sequence, we canât see back to Luca because of the ability of bacteria and archaea to move genes sideways, not just from parent cell to daughter. Thatâs not to say that Luca did not have specific characteristics that we can investigate and compare with those in living things. Itâs just that the idea of a single cell, a biological equivalent of Adam from the biblical Genesis, might be naive. If Luca was a cell, even in its most basic form, it still would have systems within it that are like their modern counterparts: DNA, RNA, proteins, ribosomes to make proteins, a cell membrane, and, crucially, a highly developed way of capturing energyâa metabolism. Otherwise, we would expect to see different and divergent mechanisms in bacteria and archaea. Not to denigrate this useful species; Lucaâs real use for science is as a proxy. If Luca is at the root of cellular life, it represents an all-dominant coagulation of what came before. Bill Martin, a brilliant and pugnacious origin-of-life biochemist we will meet properly later, says that the trouble with Luca is that, âlike love, it means different things to different people.â
Itâs been almost three and a half centuries since cells were bled, ejaculated, and fished out of their natural environment and viewed under a primitive microscope. Since then, we have picked them apart to the extent that we have earned almost full command of their faculties, acquired over four billion years. We see their commonality so clearly, a beautiful neatness where everything we discover in biology serves to refine and reinforce the truth of evolution. Itâs a wonderful state of affairs, and reflects the maturation of a science. The essential qualities of life are known and gel into a grand vision: life shares its tools, its processes, and its language. The security of a robust unifying theory of life as we know it allows us to investigate a much more difficult puzzle: where did Luca come from? As it happens, the best way to begin to understand the emergence of life on Earth is to take a hard look at where and when it happened. Therefore, we must start at the very beginning. Itâs a very good place to start.
CHAPTER 3
Hell on Earth
âLong is the way, and hard, that out of hell leads up to light.â
John Milton,
Paradise Lost
I f you want to construct a picture of
G
and
A
pairs with
U
. But
C
and
G
form a bond that is more stable at higher temperatures. Therefore, we can infer from the relative amount of
CG
bonds in ribosomes a preference for warmer conditions. This is borne out across many species, and the ribosome in which we see the highest
CG
content are from high-temperature extremophilesâin other words, organisms that thrive in heat. Where do we find such creatures? In many places, but the most impressive habitat is in and around hydrothermal vents under the sea. There, heated by a rip in the earthâs surface, plumes of noxious chemicals that can boil the sea chug out. But dozens of species thrive there: bacteria, archaea, and even large, complex creatures such as the Pompeii worm, which can endure temperatures up to eighty degrees Celsius, more than 170 degrees Fahrenheit (not least because it wears an insulating fleece of hardy bacteria).
Some models of Lucaâs ribosomes suggest that the amount of
C
s and
G
s was disproportionately high in their component parts. This might suggest a hot home for the base of life. Certainly, the discovery of extremely heat-loving (aka hyperthermophilic) archaea and bacteria in such environments as the hot springs in Yellowstone Park or submarine thermal vents supports this idea, as these organisms mostly occupy spaces at the base of evolutionary trees, as much as we can reconstruct them.
But the simple truth is we donâtâand possibly canâtâknow. Reconstructing the past using phylogenetics is a complicated art, with many confounding factors. Using the ever-changing DNA sequence, we canât see back to Luca because of the ability of bacteria and archaea to move genes sideways, not just from parent cell to daughter. Thatâs not to say that Luca did not have specific characteristics that we can investigate and compare with those in living things. Itâs just that the idea of a single cell, a biological equivalent of Adam from the biblical Genesis, might be naive. If Luca was a cell, even in its most basic form, it still would have systems within it that are like their modern counterparts: DNA, RNA, proteins, ribosomes to make proteins, a cell membrane, and, crucially, a highly developed way of capturing energyâa metabolism. Otherwise, we would expect to see different and divergent mechanisms in bacteria and archaea. Not to denigrate this useful species; Lucaâs real use for science is as a proxy. If Luca is at the root of cellular life, it represents an all-dominant coagulation of what came before. Bill Martin, a brilliant and pugnacious origin-of-life biochemist we will meet properly later, says that the trouble with Luca is that, âlike love, it means different things to different people.â
Itâs been almost three and a half centuries since cells were bled, ejaculated, and fished out of their natural environment and viewed under a primitive microscope. Since then, we have picked them apart to the extent that we have earned almost full command of their faculties, acquired over four billion years. We see their commonality so clearly, a beautiful neatness where everything we discover in biology serves to refine and reinforce the truth of evolution. Itâs a wonderful state of affairs, and reflects the maturation of a science. The essential qualities of life are known and gel into a grand vision: life shares its tools, its processes, and its language. The security of a robust unifying theory of life as we know it allows us to investigate a much more difficult puzzle: where did Luca come from? As it happens, the best way to begin to understand the emergence of life on Earth is to take a hard look at where and when it happened. Therefore, we must start at the very beginning. Itâs a very good place to start.
CHAPTER 3
Hell on Earth
âLong is the way, and hard, that out of hell leads up to light.â
John Milton,
Paradise Lost
I f you want to construct a picture of
Similar Books
