Aerobic Metabolism
- PDF / 176,229 Bytes
- 3 Pages / 595.276 x 790.866 pts Page_size
- 25 Downloads / 189 Views
ACIDOPHILES
Cross-references Biomining (Mineral Bioleaching, Mineral Biooxidation) Copper Extreme Environments Fe(II)-Oxidizing Prokaryotes Iron Sulfide Formation Ores, Microbial Precipitation and Oxidation Sulfide Mineral Oxidation
ACIDOPHILES “Acidophiles” are organisms thriving in environments below pH 5. For details, see entries “Extreme Environments,” “Biomining (Mineral Bioleaching, Mineral Biooxidation),” “Hot Springs and Geysers,” Hydrothermal Environments (Marine) and “Acid Rock Drainage.”
ACRITARCHS Acritarchs are organic-walled acid-resistant microfossils known from the Proterozoic and throughout the Phanerozoic. The position of these microfossils is still uncertain. A number of acritarch genera have been assigned to Green Algae; others are considered to bear some resemblance to the cysts of dinoflagellates. For more information, please refer to entries “Algae, Eukaryotic” and “Protozoa.”
AEROBIC METABOLISM Heribert Cypionka University of Oldenburg, Oldenburg, Germany
Synonyms Aerobic respiration; Oxygen metabolism Definition Aerobic metabolism comprises the reduction of molecular oxygen as electron acceptor of aerobic respiration, its use as cosubstrate in the degradation of certain compounds, and reactions leading to the detoxification of partially reduced oxygen species. Introduction Life has evolved in the absence of molecular oxygen (see Chapter Early Earth). Therefore, it is not surprising that basic metabolic pathways involved in growth and cell division (like DNA replication or protein synthesis) do not depend on the presence of molecular O2. The evolution of the oxygen-producing (oxygenic) phototrophs dramatically changed the situation of living organisms. Molecular oxygen raised the redox potential of the environment and enabled microorganisms to respire with a much higher energy yield than before. Although oxygen is involved in
a limited number of reactions only, its presence or absence has fundamental impact on biogeochemical processes.
Aerobic degradation of organic matter Aerobic respiration consumes a major part of the photosynthetically produced O2 and about 90% of the organic matter (see Chapter Carbon Cycle). Aerobic (oxygen-metabolizing) organisms normally oxidize their substrates completely to CO2. In most cases, O2 is not directly involved in this process. Substrate oxidation generates reduced electron carriers by means of the respiratory chain. Oxygen is reduced as the last step of the respiration process. Respiratory chain Respiration is a membrane-bound process that generates a chemiosmotic proton gradient across the membrane (Mitchell, 1966). Respiratory chains are composed of series of enzymes, which are organized in multienzyme complexes and use cofactors that allow the stepwise transport of reducing equivalents to oxygen (Figure 1). In eukaryotes (plants, animals, fungi) it takes place within the mitochondria, which are assumed to have evolved from endosymbiotic bacteria. In prokaryotes (Bacteria, Archaea), the respiratory chain is located in the cytoplasmic membrane. T
Data Loading...
