Biochemical reactions organization into pathways

Many Biochemical Reactions Require Energy Biochemical Reactions Are Localized in the Cell Biochemical Reactions Are Organized into Pathways Biochemical Reactions Are Regulated Organisms Are Biochemically Dependent on One Another... 

Metabolism is the sum total of all the enzyme-catalyzed reactions in a living organism. Many of these reactions are organized into pathways. There are two major types of biochemical pathways anabolic and catabolic. 

Biochemical reactions are frequently organized into multistep pathways. 

Biochemical reactions are organized into catabolic pathways that produce energy and reducing power, and anabolic pathways that consume these products in the process of biosynthesis. 

The thousands of enzyme-catalyzed chemical reactions in living cells are organized into a series of biochemical (or metabolic) pathways. Each pathway consists of a sequence of catalytic steps. The product of the first reaction becomes the substrate of the next and so on. The number of reactions varies from one pathway to another. For example, animals form glutamine from a-ketoglutarate in a pathway that has two sequential steps, whereas the synthesis of tryptophan by Escherichia coli requires 13 steps. Frequently, biochemical pathways have branch points. For example, chorismate, a metabolic intermediate in tryptophan biosynthesis, is also a precursor of phenylalanine and tyrosine. 

The chemical reactions in living cells are organized into a series of biochemical pathways. The pathways are controlled primarily by adjusting the concentrations and activities of enzymes through genetic control, covalent modification, allosteric regulation, and compartmentation. 

Carbon turnover in terrestrial ecosystems is mostly linked to biochemical reactions of three types of organisms. Primary biomass is produced by autotrophic organisms, mainly plants. Their biomass is transformed into new but chemically similar secondary biomass of consumers. These are connected by trophic relations in food chains and carbon recycling systems. Nonliving biomass is again mineralized by decomposers to carbon dioxide, water, and minerals. The basic biochemical pathways such as glycolysis, the pentose-phosphate cycle (Calvin cycle), and the Krebs cycle are for all organisms nearly identical. Only a few main biochemical pathways produce metabolites for biomass production, in particular cell walls. 

Metabolism is the sum of all chemical reactions in the body. Reactions that break down large molecules into smaller fragments are called catabolism reactions that build up large molecules from small pieces are called anabolism. Although the details of specific biochemical pathways are sometimes complex, all the reactions that occur follow the normal rules of organic chemical reactivity. 

It is important that chemical engineers master an understanding of metabolic engineering, which uses genetically modified or selected organisms to manipulate the biochemical pathways in a cell to produce a new product, to eliminate unwanted reactions, or to increase the yield of a desired product. Mathematical models have the potential to enable major advances in metabolic control. An excellent example of industrial application of metabolic engineering is the DuPont process for the conversion of com sugar into 1,3-propanediol,... 

All microbes, including chemoorganohetero-trophs, possess some ability to engage in reversible carboxylation (i.e., CO2-C assimilation into an organic compound) and decarboxylation reactions, some of which lead to the incorporation of a significant amount of CO2 (Wood, 1985). Here, we briefly consider the biochemical pathways that photo- and chemolithotrophic bacteria deploy in order to produce the majority of their biomass. The four major C02-fixing pathways are the Calvin cycle, the acetyl-CoA pathway, the reductive tricarboxylic acid (TCA) cycle, and the 3-hydroxypriopionate cycle. 

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