Anabolism definition

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. 

Isotestosterone and 8a, 1 Oa-testosterone can be considered as substituted testosterone derivatives where the 8-H is substituted by an alkyl group. In the case of 8a,10a-testosterone other structural features are prohibitive for biological activity. However, 8-isotestosterone displays decreased, but definite androgenic and anabolic properties. Nagata [160] prepared some 8/3-substituted testosterone homologs —8-methyl-testosterone (E-30) and others. In all cases decreased androgenic and anabolic potencies were observed. These facts point to the importance of /3-face attachment to the receptor at carbon-8. 

Bulky substituents in 10-positions decrease the androgenic and anabolic activities to a large extent. This definitely points to the /8-face attachment at C-10. Results obtained with 9a,10a-testosterone derivatives confirm the importance of /3-face attachment. However the steric requirement of the methyl group, as measured by the 2.0 A van der Waals radius [222], is no bar to /3-face attachment to the receptor at C-10. The steric requirements at C-10 can accommodate 10-methyl substitution (the presence of the 19-methyl group). 

U.S.C. section 802(41)(A)-(B) sets forth the definition of "anabolic steroids." That section provides ... 

FIGURE 19.13 Transfer of the starting materials of lipid anabolism from the mitochondrion to the cytosol. (1 is ATP-citrate lyase other symbols are as in Figure 19.10.) It is not definitely established whether acetyl-CoA is transported from the mitochondrion to the cytosol. 

Little is known of the biosynthesis, breakdown, or role of sulfatides. Two observations seem established the biosynthesis of sulfatides coincides with the appearance of myelin and studies with the aid of a radioactive precursor have established a slow but definite turnover of sulfatides in the adult brain. Consequently, the brain constantly synthesizes and degrades sulfatides. Similar anabolic and catabolic processes are likely to occur in other tissues. 

Although this is not an anabolic process, discussion of the reactions involved is included here to complete the presentation of the steps of the cycle shown in Fig. 2. The process is initiated by the oxidation of choline to betaine. Evidence that methyl transfer involves betaine, not choline was indicated by the work of Dubnofif (78), who observed that methyl transfer can occur from betaine anaerobically, but from choline only aerobically. More definite proof was provided by Muntz (79), who demonstrated that incubation of choline and homocysteine with liver homogenates yielded dimethylglycine and not dimethylaminoethanol. The former would be expected if betaine was demethylated, the latter if it was choline. 

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