Explosions that Destroy Houses Traced to Methane from Landfill

The production of methane by methanogens has several practical consequences. Methane is found in natural gas. It is a flammable gas. Methane seeping from landfills, where it is produced by methanogens degrading the waste deposits, sometimes enters nearby houses and causes explosions. Some sewage treatment facilities collect the methane that is formed

during anaerobic decomposition of wastes and use it as a source of fuel for generating heat and electric­ity. Some communities are supplied with a portion of their natural gas (methane) from this metabolic process. In the future, methane produced by mi­croorganisms may be used as a fuel for auto­mobiles.

SUMMARY

Process of Metabolism Within a Cell (pp. 158-164)

• Cells exhibit various strategies for converting chemi­cal and light energy into the energy stored within ATP, the central currency of energy of the cell. These processes of cellular metabolism also transform start­ing materials into the organic chemicals that make up the cell's structural and functional components.

Role of Enzymes (pp. 158-159)

• Enzymes are proteins that act as biological catalysts to accelerate the rates of chemical reactions by lower­ing the activation energy necessary for the reaction to occur. Different enzymes are needed to catalyze dif­ferent reactions, each cell having thousands of en­zymes, each enzyme binding only specific substrates to its active site.

Coenzymes and Oxidation-reduction

Reactions (pp. 159-160)

• An oxidation-reduction or redox reaction involves the transfer of an electron from a donor, which is oxi­dized, to an acceptor, which is reduced. All redox re­actions must be balanced. Cellular metabolism gener­ates reducing power to convert substrate materials into the more reduced molecules of the cell by cou­pling oxidation reactions with the reduction of coen­zymes.

ATP and Cellular Energy (pp. 160-161)

• All cells carry out metabolic reactions that transfer energy to ATP. ATP requires energy-releasing meta­bolic reactions for its formation. ATP's stored energy is used to drive energy-requiring biosynthetic reac­tions. Breaking an ATP high-energy bond yields 7300

calories per mole of energy. Substrate level phosphor­ylation is the generation of ATP from ADP + Pj cou­pled to energetically favorable reactions. The forma­tion of ATP can also be driven by a protonmotive force in chemiosmosis.

Metabolic Pathways and Carbon Flow (pp. 161-162)

• The metabolic pathways utilized in ATP generation involve various intermediary metabolites linked to­gether in a series of small steps to form unified bio­chemical pathways. In a catabolic pathway, larger molecules are split into smaller ones. Cells form rela­tively small molecules that can act as the basis for the carbon skeletons of larger macromolecules that are synthesized in anabolic (biosynthetic) pathways.

Autotrophic and Heterotrophic

Metabolism (pp. 162-164)

• The synthesis of ATP can be achieved autotrophi- cally—through the oxidation of inorganic substrates or through the conversion of light energy to chemical energy—or may be generated heterotrophically through the utilization of organic substrates.

Metabolic Pathways (pp. 164-187)

Respiration (pp. 165-171)

• The Embden-Meyerhof pathway of glycolysis con­verts the 6-carbon molecule glucose into two mole­cules of the 3-carbon molecule pyruvate, plus two molecules of reduced coenzyme and two molecules of ATP.

• Glycolysis is the first step in all pathways of carbohy­drate metabolism. Its product, pyruvate, feeds into

metabolic PATHWAYS 187