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1.1 Cellular Foundations All organism Phototrophs Chemotrophs (energy from (energy from chemical light) Autotroph Heterotrophs Heterotroph (carbon from (carbon from (carbon from organic organIc compounds Cyanobacteria Examples Plants ° Purple bacteria Green bacteria L Ort InorganI Examples: Examples Sulfur bacteria Most prokaryotes FIGURE 1-5 Organisms can be classified according to their source All nonphototrophic of energy (sunlight or oxidizable chemical compounds)and their eukaryotes source of carbon for the synthesis of cellular material. domains, sometimes called Archaea and Bacteria. All eu- atoms exclusively from CO2(that is, no chemotrophs karyotic organisms, which make up the third domain, are autotrophs), but the chemotrophs may be further karya, evolved from the same branch that gave rise classified according to a different criterion whether the to the Archaea; archaebacteria are therefore more fuels they oxidize are inorganic (lithotrophs )oror- closely related to eukaryotes than to eubacteria ganic (organotrophs) Within the domains of archaea and bacteria are sub Most known organisms fall within one of these four groups distinguished by the habitats in which they live. broad categories-autotrophs or heterotrophs among the In aerobie habitats with a plentiful supply of oxygen, photosynthesizers, lithotrophs or organotrophs among some resident organisms derive energy from the trans- the chemical oxidizers. The prokaryotes have several gen- fer of electrons from fuel molecules to oxygen. Other eral modes of obtaining carbon and energy. Escherich environments are anaerobic, virtually devoid of oxy- coli, for example, is a chemoorganoheterotroph; it re- gen, and microorganisms adapted to these environments quires organic compounds from its environment as fuel obtain energy by transferring electrons to nitrate(form- and as a source of carbon. Cyanobacteria are photo- ing N2), sulfate(forming HS), or CO2(forming CHa) lithoautotrophs; they use sunlight as an energy source Many organisms that have evolved in anaerobic envi- and convert CO2 into biomolecules. We humans, like E ronments are obligate anaerobes: they die when ex- coli, are chemoorganoheterotrophs posed to oxygen. We can classify organisms according to how they obtain the energy and carbon they need for synthesiz Escherichia coli Is the Most-Studied Prokaryotic Cell ng cellular material (as summarized in Fig. 1-5. There Bacterial cells share certain common structural fea- are two broad categories based on energy sources: pho- tures, but also show group-specific specializations (fig totrophs (Greek trophe, "nourishment") trap and use 1-6). E. coli is a usually harmless inhabitant of the hu- sunlight, and chemotrophs derive their energy from man intestinal tract. The E coli cell is about 2 um long oxidation of a fuel. All chemotrophs require a source of and a little less than I um in diameter. It has a protec- organic nutrients; they cannot fix CO2 into organic com- tive outer membrane and an inner plasma membrane pounds. The phototrophs can be further divided into that encloses the cytoplasm and the nucleoid. Between those that can obtain all needed carbon from CO2(au- the inner and outer membranes is a thin but strong layer totrophs) and those that require organic nutrients of polymers called peptidoglycans, which gives the cell heterotrophs). No chemotroph can get its carbon its shape and rigidity. The plasma membrane and thedomains, sometimes called Archaea and Bacteria. All eukaryotic organisms, which make up the third domain, Eukarya, evolved from the same branch that gave rise to the Archaea; archaebacteria are therefore more closely related to eukaryotes than to eubacteria. Within the domains of Archaea and Bacteria are subgroups distinguished by the habitats in which they live. In aerobic habitats with a plentiful supply of oxygen, some resident organisms derive energy from the transfer of electrons from fuel molecules to oxygen. Other environments are anaerobic, virtually devoid of oxygen, and microorganisms adapted to these environments obtain energy by transferring electrons to nitrate (forming N2), sulfate (forming H2S), or CO2 (forming CH4). Many organisms that have evolved in anaerobic environments are obligate anaerobes: they die when exposed to oxygen. We can classify organisms according to how they obtain the energy and carbon they need for synthesizing cellular material (as summarized in Fig. 1–5). There are two broad categories based on energy sources: phototrophs (Greek trophe- , “nourishment”) trap and use sunlight, and chemotrophs derive their energy from oxidation of a fuel. All chemotrophs require a source of organic nutrients; they cannot fix CO2 into organic compounds. The phototrophs can be further divided into those that can obtain all needed carbon from CO2 (autotrophs) and those that require organic nutrients (heterotrophs). No chemotroph can get its carbon atoms exclusively from CO2 (that is, no chemotrophs are autotrophs), but the chemotrophs may be further classified according to a different criterion: whether the fuels they oxidize are inorganic (lithotrophs) or organic (organotrophs). Most known organisms fall within one of these four broad categories—autotrophs or heterotrophs among the photosynthesizers, lithotrophs or organotrophs among the chemical oxidizers. The prokaryotes have several general modes of obtaining carbon and energy. Escherichia coli, for example, is a chemoorganoheterotroph; it requires organic compounds from its environment as fuel and as a source of carbon. Cyanobacteria are photolithoautotrophs; they use sunlight as an energy source and convert CO2 into biomolecules. We humans, like E. coli, are chemoorganoheterotrophs. Escherichia coli Is the Most-Studied Prokaryotic Cell Bacterial cells share certain common structural features, but also show group-specific specializations (Fig. 1–6). E. coli is a usually harmless inhabitant of the human intestinal tract. The E. coli cell is about 2 m long and a little less than 1 m in diameter. It has a protective outer membrane and an inner plasma membrane that encloses the cytoplasm and the nucleoid. Between the inner and outer membranes is a thin but strong layer of polymers called peptidoglycans, which gives the cell its shape and rigidity. The plasma membrane and the 1.1 Cellular Foundations 5 Heterotrophs (carbon from organic compounds) Examples: •Purple bacteria •Green bacteria Autotrophs (carbon from CO2) Examples: •Cyanobacteria •Plants Heterotrophs (carbon from organic compounds) Phototrophs (energy from light) Chemotrophs (energy from chemical compounds) All organisms Lithotrophs (energy from inorganic compounds) Examples: •Sulfur bacteria •Hydrogen bacteria Organotrophs (energy from organic compounds) Examples: •Most prokaryotes •All nonphototrophic eukaryotes FIGURE 1–5 Organisms can be classified according to their source of energy (sunlight or oxidizable chemical compounds) and their source of carbon for the synthesis of cellular material. 8885d_c01_005 12/20/03 7:04 AM Page 5 mac76 mac76:385_reb: