Catabolic/Anabolic reactions

Metabolic reactions are categorized into two types, anabolic and catabolic. Anabolic reactions construct complex molecules from simple molecules, usually while using up energy that becomes stored in chemical bonds. Catabolic reactions break down complex molecules into multiple simple molecules, usually while releasing energy. 

With reference to the free energy as a characteristic of metabolism one may say that catabolic reactions proceed with a release of energy and anabolic ones, with a consumption of energy The anabolic reactions can proceed only as closely coupled to the catabolic reactions. High-energy, or macroergic, compounds act as energetic mediators between these two types of reactions. 

Anabolic metabolic pathways are the flip side of catabolic ones. Anabolic reactions are biosynthetic that is, they create complex molecules out of simpler ones. Anabolic pathways are reductive in nature and consume energy. In all these ways, anabolic pathways stand in contrast to catabolic ones. It is frequently the case that the end product of an anabolic pathway will inhibit the first enzyme in the same pathway. This makes a good deal of sense. Anabolic pathways require energy and if there is enough end product available there is little reason to keep making more of it. So an excess of the end product simply turns off the pathway by inhibiting the first enzyme ... 

The oxidation of pyruvate is an important catabolic process, but pyruvate has anabolic fates as well. It can, for example, provide the carbon skeleton for the synthesis of the amino acid alanine. We return to these anabolic reactions of pyruvate in later chapters. 

NAD-linked dehydrogenases remove two hydrogen atoms from their substrates. One of these is transferred as a hydride ion ( II ) to NAD+ the other is released as H+ in the medium (see Fig. 13-15). NADH and NADPH are water-soluble electron carriers that associate reversibly with dehydrogenases. NADH carries electrons from catabolic reactions to their point of entry into the respiratory chain, the NADH dehydrogenase complex described below. NADPH generally supplies electrons to anabolic reactions. Cells maintain separate pools of NADPH and NADH, with different redox potentials. This is accomplished by holding the ratios of [reduced form]/[oxidized form] relatively high for NADPH and relatively low for NADH. Neither NADH nor NADPH can cross the inner mitochondrial membrane, but the electrons they carry can be shuttled across indirectly, as we shall see. 

Anabolic reactions combine small molecules, such as amino acids, to form complex molecules, such as proteins (Figure 8.4). Anabolic reactions require energy, which is generally provided by the break down of ATP to ADP and Pj. Anabolic reactions often involve chemical reductions in which the reducing power is most frequently provided by the electron donor NADPH (see p. 145). Note that catabolism is a convergent process—that is, a wide variety of molecules are transformed into a few common end products. By con trast, anabolism is a divergent process in which a few biosynthetic precursors form a wide variety of polymeric or complex products. 

Introduction to metabolism Definition of catabolic and anabolic pathways INTRODUCTION TO METABOLISM (p. 89) Most pathways can be classified as either catabolic (they degrade complex molecules to a few simple products, such as C02, NH3, and water) or anabolic (they synthesize complex end-products from simple precursors). Catabolic reactions also capture chemical energy in the form of ATP from the degradation of energy-rich molecules. Anabolic reactions require energy, which is generally provided by the breakdown of ATP. 

The types of biomolecules produced by anabolism are the same as the types found in food—carbohydrates, lipids, proteins, and nucleic acids. These products of anabolism are, if you will, the hosts own version of what the food once was. And if the host ever becomes food, anabolic reactions in the subsequent host will result in different versions of the molecules. Thus, organisms in a food chain live off one another by absorbing one another s energy via catabolic reactions and then rearranging the remaining atoms and molecules via anabolic reactions into the biomolecules they need to survive. 

Both statements are valid but the second statement, (b), states more accurately why it is that we need vitamins. Vitamin-deficiency diseases, Such as scurvy, result when certain catabolic and anabolic reactions are not able to proceed efficiently in the absence of these important nutrients. 

Variation in reaction rates as a function of the energy charge. As the energy charge increases, the rate of catabolic reactions decreases. Meanwhile, the rate of anabolic reactions increases. The combined effect is to stabilize the energy charge at a value around 0.9. 

Figure 4 summarizes the result of these experiments. All reactions associated with carbohydrate metabolism are decreased by exposure to radiation, while all associated with the citric acid cycle and acetate catabolism are increased. Also, in every case studied, anabolic reactions were reduced by radiation. 

No. most catabolic reactions take place in the mitochondria anabolic reactions in the cytosol. 28.6 (a) carbon dioxide (b) water (c) sunlight... 

Since a molecule of water is eliminated for each linkage formed, the anabolic reactions leading to macromolecule formation are dehydration reactions. Recall from Section 4.2 that when macro-molecular nutrient molecules are digested prior to their entering the body s system, a molecule of water is added for each linkage broken — a hydrolysis reaction. The energy required for the anabolic synthesis of macromolecules is provided by catabolic processes of glycolysis, the citric acid cycle, and electron transport. 

Almost all physiological processes in plants take place in the presence of water. Essential anabolic reactions (photosynthesis, assimilation, and protein synthesis), and catabolic ones (respiration and hydrolysis) occur in an aqueous cellular environment. Essential elements absorbed by plant roots, and the foods and other metabolites manufactured by the leaves and other tissues, move in aqueous solution from the regions of absorption or manufacture to other parts of the plant where additional anabolic reactions and ultimate food storage take place. Water is the major constituent of protoplasm, and is particularly abundant in young and growing tissues. 

All anabolic reactions are represented here by the term a whereas 3X represents all catabolic reactions. In the most general case, a and 3 could each be functions of other metabolites and of X itself and are always positive. Initially, however, I shall... 

The use of fumarate as an endogenous electron acceptor requires a well-controlled balance between the various catabolic and anabolic reactions in the cell. Depending on the metabolic state of the cell, the NAD FI pool might... 

In addition to the obvious role in the catabolism of macromolecules, the TCA cycle provides numerous intermediates for anabolic reactions, such as the synthesis of porphyrins from succinyl-CoA, purines from a-ketoglutarate, pyrimidines from fumarate and oxaloacetate, and proteins from amino acids derived from oxaloacetate, fumarate, and a-ketoglutarate. 

Those reactions that require energy—such as the synthesis of glucose, fats, or DNA—are called anabolic reactions or anabolism. The useful forms of energy that are produced in catabolism are employed in anabolism to generate complex structures from simple ones, or energy-rich states from energy-poor ones. 

Even in the simplest cells, such as bacteria, there are at least a thousand such reactions. Regardless of the number, all cellular reactions can be classified as one of two types of metabolism anabolism and catabolism. These reactions, while opposite in nature, are linked... 

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