Biochemical pathways catabolic

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. 

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. 

In this simplified overview of metabolism, the anabolic and catabolic pathways of the major food molecules in heterotrophs (i.e., those biochemical pathways that synthesize, degrade, or interconvert important biomolecules and generate energy) are illustrated. 

There are two types of metabolic pathways catabolic, involving the breakdown of biochemicals into simpler compounds, and anabolic, involving the synthesis of biochemicals from simpler molecules. Each living cell has thousands of distinct metabolic reactions. Each reaction is catalyzed by an enzyme and is linked to other reactions through a pathway. How can you keep them all straight It is nearly impossible to memorize them. The purpose of this chapter is to provide an organizational framework to metabolism that allows you to view it as something other than a collection of disjointed pathways. 

Which of the following are reasons the biochemical pathway for the catabolism of a molecule is almost never the same as the pathway for the biosynthesis of that molecule ... 

Many different groups of bacteria, including Bacillus, Pseudomonas, and Thiobacillus, are capable of denitrification. The primary biochemical pathways for organic substrate oxidation by denitri-fiers are similar to that described for aerobic catabolism. Because most of the denitrifiers are facultative anaerobes, they possess a functional TCA cycle that allows them to metabolize substrates completely to carbon dioxide and water. Many denitrifiers do not produce extracellular enzymes required for hydrolysis of polymers thus, they generally rely on hydrolytic enzymes and fermenters to provide readily available substrates (Ljundahl and Erickson, 1985). 

FIGURE 5.3 The biochemical pathway utilized by P. putida ML2 in the catabolism of benzene [fignre taken from 19]. 

Figure 5. The biocatalytic pathway (boxed arrows) created for microbial conversion of D-glucose into cis, cw-muconate from the perspective of the biochemical pathways from which the enzymes were recruited. Conversion of D-glucose into DHS requires transketolase (tkt) from the pentose phosphate pathway and DAHP synthase (aroF, aroG, aroH)y DHQ synthase aroB and DHQ dehydratase aroD) from the common pathway of aromatic amino acid biosynthesis. Conversion of DHS into catechol requires DHS dehydratase (aroZ, enzyme A) from hydroaromatic catabolism, protocatechuate decarboxylase aroY, enzyme B), and catechol 1,2-dioxygenase (caM, enzyme C) from the benzoate branch of the p-ketoadipate pathway. (Adapted and reproduced with permission from ref. 21.)...

Figure 8.1 Biochemical pathways involved in glucose catabolism in Pseudomonas putida KT2440. The metabolic network depicted is sketched around four main metabolic blocks, identified with different colors (i) the peripheral oxidative pathways, that encompass the oxidative transformation of glucose into gluconate and 2-ketogluconate (and the corresponding phosphorylated derivatives of these metabolites) (ii) the Embden-Meyerhof-Pamas (EMP) pathway (nonfunctional, due to the absence of a 6-phosphofructokinase activity) (iii) the...

Biochemical pathways may be described as catabolic, anabolic (biosynthetic), amphibolic or anaplerotic. The principal function of a catabolic sequence is to degrade (usually by an oxidative process) simple organic molecules derived from the breakdown of polymers (e.g. amino acids from proteins) and retain some of the free energy released in a biologically useful form. Anabolic pathways consume energy and synthesize (usually by a reductive process) the simple molecules which are assembled into proteins, nucleic acids, carbohydrate polymers and lipids. Amphibolic pathways, such as the tricarboxylic acid cycle, have both catabolic and anabolic properties. They are central metabolic pathways which furnish, from catabolic sequences, the intermediates which form the substrates of anabolic processes. The... 

Plant cells produce far more chemical compounds than is necessary for their basic functions i.e., biochemical pathways for survival and propagation. Basic or primary metabolism refers to all biochemical processes for the normal anabolic and catabolic pathways, which result in assimilation, respiration, transport, and differentiation. Basic or primary metabolism is shared by all cells, while secondary metabolism generates diverse and seemingly less essential or nonessential byproducts called secondary products. The secondary products are the colors, flavors, and smells, which are the sources of fine chemicals such as drugs, insecticides, dyes, flavors, and fragrances, and plant-growth regulators found in medicinal plants. 

Figure 29.1 An overview of catabolic pathways for the degradation of food and the production of biochemical energy. The ultimate products of food catabolism are C02 and H2O, with the energy released in the citric acid cycle used to drive the endergonic synthesis of adenosine triphosphate (ATP) from adenosine diphosphate (ADP) plus phosphate ion, HOPO32-.

Carbohydrate metabolism in the organism tissues encompasses enzymic processes leading either to the breakdown of carbohydrates (catabolic pathways), or to the synthesis thereof (anabolic pathways). Carbohydrate breakdown leads to energy release or intermediary products that are necessary for other biochemical processes. The carbohydrate synthesis serves for replenishment of polysaccharide reserve or for renewal of structural carbohydrates. The effectiveness of various routes of carbohydrate metabolism in tissues and organs is defined by the availability of appropriate enzymes in them. 

Zinc protoporphyrin IX is a normal metabolite that is formed in trace amounts during haem biosynthesis. However, in iron deficiency or in impaired iron utilization, zinc becomes an alternative substrate for ferrochelatase and elevated levels of zinc protoporphyrin IX, which has a known low affinity for oxygen, are formed. This zinc-for-iron substitution is one of the first biochemical responses to iron depletion, and erythrocyte zinc protoporphyrin is therefore a very sensitive index of bone-marrow iron status (Labbe et ah, 1999). In addition, zinc protoporphyrin may regulate haem catabolism by acting as a competitive inhibitor of haem oxygenase, the key enzyme of the haem degradation pathway. However, it has been reported... 

The study of mutation in bacteria (and bacterial vimses) has had a fundamental role in the science of genetics in the twentieth century. In particular, the unraveling of biochemical anabolic and catabolic pathways, the identification of DNA as the hereditary material, knowledge of the fine structure of the gene, and the nature of gene regulation, and so on, have all been aided by bacterial mutants. 

The amino acids falling into each category are presented in Table 8.9. The pathways in processes (i) and (ii) are described in Appendix 8.3. The combined process of deamination plus transamination illustrates important principles in amino acid catabolism. These lead to an appreciation of some of the biochemical and physiological functions of amino acids that are important in health and disease. 

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