Reductive biosynthesis

NADPH formed in the oxidative phase is used to reduce glutathione, GSSG (see Box 14-3) and to support reductive biosynthesis. The other product of the oxidative phase is ribose 5-phosphate, which serves as precursor for nucleotides, coenzymes, and nucleic acids. In cells that are not using ribose 5-phosphate for biosynthesis, the nonoxidative phase recycles six molecules of the pentose into five molecules of the hexose glucose 6-phosphate, allowing continued production of NADPH and converting glucose 6-phosphate (in six cycles) to C02. 

Answer The reductive pentose phosphate pathway regenerates ribulose 1,5-bisphosphate from triose phosphates produced during photosynthesis, in a series of reactions involving sugars of three, four, five, six, and seven carbons and the enzymes transaldolase and transketo-lase. The oxidative pentose phosphate pathway plays a different metabolic role it provides NADPH for reductive biosynthesis and pentose phosphates for nucleotide synthesis. 

An activated carrier of electrons for reductive biosynthesis. High-potential electrons are required in most biosyntheses because the precursors are more oxidized than the products. Hence, reducing power is needed in addition to ATP. For example, in the biosynthesis of fatty acids, the keto group of an added two-carbon unit is reduced to a methylene group in several steps. This sequence of reactions requires an input of four electrons. 

The pentose phosphate pathway meets the need of all organisms for a source of NADPH to use in reductive biosynthesis (Table 20.2). This pathway consists of two phases the oxidative generation of NADPH and the nonoxidative interconversion of sugars (Figure 20.19). In the oxidative phase, NADPH is generated when glucose 6-phosphate is oxidized to ribose 5-phosphate. This five-carbon sugar and its derivatives are components of RNA and DNA, as well as ATP, NADH, FAD, and coenzyme A. 

In anabolic role it maintains microsomal reductive biosynthesis and photolsynthesis. 

A. It is an alternative process to glycolysis for oxidation of glucose It functions to provide NADPH for reductive biosynthesis. 

NADPH is used for reductive biosynthesis (particularly of fatty adds) and for protection against oxidative damage. 

Which of the compounds in the figure in question 321 is the precursor of the electron donor used in reductive biosynthesis ... 

The pentose-phosphate pathway produces NADPH, for reductive biosynthesis, and pentose phosphates, for nucleotide synthesis. 

Reduced Ferredoxin in Reductive Biosynthesis Constructing the Monomer Units... 

An activated carrier of electrons for reductive biosynthesis. High-potential electrons are required in most biosyntheses because the precursors are more oxidized than the products. Hence, reducing power is needed in addition to... 

The pathway borrows heavily from the nonoxidative branch of the pentose phosphate pathway and from gluconeogenesis. Without doubt, the pathways yield sugars as well as NADPH for reductive biosynthesis. Thus, only a few new enzymes would have to evolve through mutations to enable the complete Calvin cycle to function. 

C42H5 ClN4NiO,7, Mr 1006.04, uv, (pentamethyl ester, F 430 M in HjO) 431,418,296,274 nm. F. belongs to the structural class of the hydroporphyrins. Occurrence F. (coenzyme F 430), is the prosthetic group of methyl-coenzyme M reductase, which catalyzes the last step of methane formation in methano-genic bacteria. The mechanism of formation of methane from methyl-coenzyme M (H3C-S-CH2-CH2-SOJ) is still unknown. However, the central nickel atom in F. most certainly participates in the reduction. Biosynthesis F. is formed from 5-amino-4-oxova-leric acid via the normal biosynthetic route for porphi-noid compounds. The 2- and 7-methyl groups originate from 5-adenosylmethionine. 

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