Origin of Metabolism
Origin of Metabolism
Living cells today are organized systems with complex and highly ordered sequences of enzyme-mediated reactions. How did such vastly complex metabolic schemes develop? The exact history of this phase of life’s evolution is unknown. We present here a model of the simplest sequence of events that could explain the origin of the observed metabolic properties of living systems. We present here the traditional view that the first organisms were primary heterotrophs. Carl Woese finds it easier to visualize membrane-associated molecular aggregates that absorbed visible light and converted it with some efficiency into chemical energy. Thus the first organisms would have been autotrophs.Woese also suggests that the earliest “metabolism”may have consisted of numerous chemical reactions catalyzed by nonprotein cofactors (substances necessary for the function of many of the protein enzymes in living cells).These cofactors would have been associated with membranes.
Organisms that can synthesize their food from inorganic sources using light or another source of energy are called autotrophs (Gr. autos, self, + trophos, feeder) (Figure 2-14). Organisms lacking this ability must obtain their food supplies directly from the environment and are known as heterotrophs (Gr. heteros, another, + trophos, feeder). The earliest microorganisms are sometimes called primary heterotrophs because they relied on environmental sources for their food and existed prior to the evolution of any autotrophs. They were probably anaerobic organisms similar to bacteria of the genus Clostridium. Because chemical evolution had supplied generous stores of nutrients in the prebiotic soup, the earliest organisms would not have been required to synthesize their own food.
Protocells able to convert inorganic precursors to a required nutrient would have had a tremendous selective advantage over the primary heterotrophs in areas where nutrients became depleted from the environment. Evolution of autotrophic organisms most likely required acquisition of enzymatic activities to catalyze conversion of inorganic molecules to more complex ones, such as carbohydrates. The numerous enzymes of cellular metabolism appeared when cells became able to utilize proteins for catalytic functions.
Living cells today are organized systems with complex and highly ordered sequences of enzyme-mediated reactions. How did such vastly complex metabolic schemes develop? The exact history of this phase of life’s evolution is unknown. We present here a model of the simplest sequence of events that could explain the origin of the observed metabolic properties of living systems. We present here the traditional view that the first organisms were primary heterotrophs. Carl Woese finds it easier to visualize membrane-associated molecular aggregates that absorbed visible light and converted it with some efficiency into chemical energy. Thus the first organisms would have been autotrophs.Woese also suggests that the earliest “metabolism”may have consisted of numerous chemical reactions catalyzed by nonprotein cofactors (substances necessary for the function of many of the protein enzymes in living cells).These cofactors would have been associated with membranes.
Organisms that can synthesize their food from inorganic sources using light or another source of energy are called autotrophs (Gr. autos, self, + trophos, feeder) (Figure 2-14). Organisms lacking this ability must obtain their food supplies directly from the environment and are known as heterotrophs (Gr. heteros, another, + trophos, feeder). The earliest microorganisms are sometimes called primary heterotrophs because they relied on environmental sources for their food and existed prior to the evolution of any autotrophs. They were probably anaerobic organisms similar to bacteria of the genus Clostridium. Because chemical evolution had supplied generous stores of nutrients in the prebiotic soup, the earliest organisms would not have been required to synthesize their own food.
 |
| Figure 2-14 Koala, a heterotroph, feeding on a eucalyptus tree, an autotroph. All heterotrophs depend for their nutrients directly or indirectly on autotrophs that capture the sun’s energy to synthesize their own nutrients. |
Protocells able to convert inorganic precursors to a required nutrient would have had a tremendous selective advantage over the primary heterotrophs in areas where nutrients became depleted from the environment. Evolution of autotrophic organisms most likely required acquisition of enzymatic activities to catalyze conversion of inorganic molecules to more complex ones, such as carbohydrates. The numerous enzymes of cellular metabolism appeared when cells became able to utilize proteins for catalytic functions.
Support our developers
