Cycles, biochemical

A certain enzyme-catalyzed reaction in a biochemical cycle has an equilibrium constant that is 10 times the equilibrium constant of the next step in the cycle. If the standard Gibbs free energy of the first reaction is —200. k -mol 1, what is the standard Gihhs free energy of the second reaction ... 

Orgel, L.E. (2000). Self-organizing biochemical cycles. Proc. Natl. Acad. Sci. (USA), 97,12503-12507... 

In the study of the origin of life on earth, the element carbon is essential. Carbon is a required component of the fundamental molecules of life amino acids, bases, and sugars. In addition, a large variety of carbon compounds is necessary in the complex biochemical cycles of living organisms. The physical and chemical nature and geometry of the carbon atom make it well suited to form the vast array of molecules involved in the chemistry of life. 

Metalls and metalloids are characterized by special ecochemical features. They are not biodegradable, but undergo a biochemical cycle during which transformations into more or less toxic species occur. They are accumulated by organisms and cause increased toxic effects in mammals and man after long term exposure [55]. 

A clear avenue of future research is to explore the S-Fe redox couple in biologic systems. Bacterial sulfate reduction and DIR may be spatially decoupled, dependent upon the distribution of poorly crystalline ferric hydroxides and sulfate (e.g., Canfield et al. 1993 Thamdrup and Canfield 1996), or may be closely associated in low-suUate environments. Production of FIjS from bacterial sulfate reduction may quickly react with Fefll) to form iron sulfides (e.g., Sorensen and Jeorgensen 1987 Thamdrup et al. 1994). In addition to these reactions, Fe(III) reduchon may be coupled to oxidation of reduced S (e.g., Thamdrup and Canfield 1996), where the net result is that S and Fe may be cycled extensively before they find themselves in the inventory of sedimentary rocks (e.g., Canfield et al. 1993). Investigation of both S and Fe isotope fractionations produced during biochemical cycling of these elements will be an important future avenue of research that will bear on our understanding of the isotopic variations of these elements in both modem and ancient environments. 

Benner, R. H., Louchouarn, P, and Amon, R. M. W. (2005). Terrigeneous dissolved organic matter in the Arctic Ocean and its transport to surface and deep waters of the North Atlantic. Global Biochem. Cycles 19. GB2025, doi 10.1029/2004 GB002398. 

Grannas, A. M., Shewpson, P. B., and Filley, T. R. (2004). Photochemistry and nature of organic matter in arctic and antarctic snow. Global Biochem. Cycles 18, GB1006, doi 10.1029/2003GB002133. 

Hill, T.L. Free Energy Transduction and Biochemical Cycle Kinetics, Springer-Verlag New York, 1989. 

Anaplerotic reactions replace substances present in catalytic amounts, which are indispensable for the operation of biochemical cycles. Which is an anaplerotic reaction ... 

There are >40 distinct molybdenum enzymes that occur in all classes of living systems and are especially important in the biochemical cycles of carbon, nitrogen, and sulfur (24b). The majority of the molybdenum enzymes, with notable exceptions including the nitrogenases (25-28) and a 2-hydroxyglutaryl-CoA dehydratase (10), catalyze a conversion of the type [Eq. 1], that is, the net effect of the catalysis corresponds to the transfer of an oxygen atom to or from the substrate. 

Kreb s cycle Biochemical cycle in cellular aerobic metabolism where acetyl CoA is combined with oxaloacetate to form citric acid the resulting citric acid is converted into a number of other chemicals, eventually reforming oxaloacetate NADH, some ATP, and FADH2 are produced and carbon dioxide is released. 

As for chloroplast membranes, various compounds in mitochondrial membranes accept and donate electrons. These electrons originate from biochemical cycles in the cytosol as well as in the mitochondrial matrix (see Fig. 1-9) —most come from the tricarboxylic acid (Krebs) cycle, which leads to the oxidation of pyruvate and the reduction of NAD+ within mitochondria. Certain principal components for mitochondrial electron transfer and their midpoint redox potentials are indicated in Figure 6-8, in which the spontaneous electron flow to higher redox potentials is toward the bottom of the figure. As for photosynthetic electron flow, only a few types of compounds are involved in electron transfer in mitochondria—namely, pyridine nucleotides, flavoproteins, quinones, cytochromes, and the water-oxygen couple (plus some iron-plus-sulfur-containing centers or clusters). 

As has already been mentioned, oxidation of methane led to the formation of free carbon which apparently was involved in biochemical cycles. Therefore the oldest sedimentary rocks could have contained both juvenile carbon, produced in chemical oxidation of methane, and biogenic carbon, formed in the decomposition of organisms. 

Matter (Flow) Balance, Metabolic Strategy and Estimation of Loss Processes (Exit Order) Within Autocatalytic Biochemical Cycles... 

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