Glycolysis glyceraldehyde-3-phosphate converted

During glycolysis, glyceraldehyde 3-phosphate is converted to 1,3-bisphosphoglycerate and the equilibrium of the adenylate kinase reaction lies in favor of 3-phosphoglycerate, so the metabolites are drawn through the pathway of reactions. 

Fig. 8.22. Isomerases rearrange atoms within a molecule. In the pathway of glycolysis, triose phosphate isomerase converts dihydroxyacetone phosphate to glyceraldehydes 3-phos-phate by rearranging hydrogen atoms. No other substrates or products of the reaction exist.

Fig. 29.3. Fructose metabolism. The pathway for the conversion of fructose to dihydroxy-acetone phosphate and glyceraldehyde 3-phosphate is shown in blue. These two compounds are intermediates of glycolysis and are converted in the liver principally to glucose, glycogen, or fatty acids. In the liver, aldolase B cleaves both fructose 1-phosphate in the pathway for fructose metabolism, and fructose 1,6-bisphosphate in the pathway for glycolysis.

FIGURE 17.3 Conversion of pyruvate to glyceraldehyde-3-phosphate. In the first phase of glycolysis, five reactions convert a molecule of glucose to two molecules of glyceraldehyde-3-phosphate. 

In the first stages of glycolysis, glucose is converted to two molecules of glyceraldehyde-3-phosphate. 

In the second phase of glycolysis, glyceraldehyde-3-phosphate is converted to pyruvate. 

Glycerophosphate dehydrogenase, from yeast, converts a-glycerophosphoric acid into glyceraldehyde phosphate, and subsequently into phosphoglyceric acid, all of which participate in glycolysis. Adenosine triphosphate is the co-enzyme of the... 

Further steps m glycolysis use the d glyceraldehyde 3 phosphate formed m the aldolase catalyzed cleavage reaction as a substrate Its coproduct dihydroxyacetone phosphate is not wasted however The enzyme triose phosphate isomerase converts dihydroxyacetone phosphate to d glyceraldehyde 3 phosphate which enters the glycol ysis pathway for further transformations... 

This reaction is followed by another phosphorylation with ATP catalyzed by the enzyme phosphofructoki-nase (phosphofructokinase-1), forming fructose 1,6-bisphosphate. The phosphofructokinase reaction may be considered to be functionally irreversible under physiologic conditions it is both inducible and subject to allosteric regulation and has a major role in regulating the rate of glycolysis. Fructose 1,6-bisphosphate is cleaved by aldolase (fructose 1,6-bisphosphate aldolase) into two triose phosphates, glyceraldehyde 3-phosphate and dihydroxyacetone phosphate. Glyceraldehyde 3-phosphate and dihydroxyacetone phosphate are inter-converted by the enzyme phosphotriose isomerase. 

Triose phosphate isomerase is one of the enzymes of glycolysis (see Section 15.2) and is responsible for converting dihydroxyacetone phosphate into glyceraldehyde 3-phosphate by a two-stage enolization process. An intermediate enediol is involved - this common enol can revert to a keto form in two ways, thus providing the means of isomerization. 

E. In the second phase of glycolysis, two glyceraldehyde 3-phosphate molecules from glucose are converted to pyruvate in conjunction with several important energy-generating reactions (Figure 6—1). 

Outline the reactions by which glyceraldehyde 3-phosphate is converted to 3-phosphoglycerate with coupled synthesis of ATP in the glycolysis pathway. Show important mechanistic details. 

So in summary, three glucose-6-phosphate (3.1) molecules (3 x C6) are oxidized to three ribulose-5-phosphate (3.13) residues (3 x C5) and three molecules of C02 (3 x Ci) under generation of six molecules of NADPH. The three ribulose-5-phosphate residues are then converted to one glyceraldehyde-3-phosphate (3.14) molecule (lx C3) and two fructose-6-phosphate (3.2) molecules (2 x C6). Fructose-6-phosphate can be converted to glucose-6-phosphate and reenter the oxidative part of the pentose phosphate pathway. Fructose-6-phosphate and glyceraldehydes can also serve as intermediates in glycolysis (Section 5.1), which offers the cell considerable flexibility in terms of its metabolic flux. 

PEP is converted to fructose 1,6-bisphosphate in a series of steps that are a direct reversal of those in glycolysis (see Topic J3), using the enzymes enolase, phosphoglycerate mutase, phosphoglycerate kinase, glyceraldehyde 3-phosphate dehydrogenase, triose phosphate isomerase and aldolase (see Fig 1). This sequence of reactions uses one ATP and one NADH for each PEP molecule metabolized. 

If at any time only a little ribose 5-phosphate is required for nucleic acid synthesis and other synthetic reactions, it will tend to accumulate and is then converted to fructose 6-phosphate and glyceraldehyde 3-phosphate by the enzymes transketolase and transaldolase. These two products are intermediates of glycolysis. Therefore, these reactions provide a link between the pentose phosphate pathway and glycolysis. The outline reactions are shown below. 

NADPH, fructose 6-phosphate and glyceraldehyde 3-phosphate can be taken from glycolysis and converted into ribose 5-phosphate by reversal of the transketolase and transaldolase reactions. 

Much of the glyceraldehyde 3-phosphate produced by the Calvin cycle in chloroplasts is exported to the cytosol and used to produce the disaccharide, sucrose. First the glyceraldehyde 3-phosphate is converted to fructose 6-phos-phate and glucose 1-phosphate. The chemical reactions involved are essentially a reversal of glycolysis (see Topic J3). The glucose 1-phosphate is then converted to UDP-glucose and this reacts with fructose 6-phosphate to synthesize sucrose 6-phosphate ... 

Fig. 8.2 Glycolysis and related pathways. Glycolysis is a central metabolic machinery in which one mole of glucose is catabolized to two moles of pyruvate, NADH, and ATP. Under aerobic conditions, pyruvate is further oxidized by mitochondrial system. In erythrocytes DHAP is a dead-end product however, in brain it can be converted into direction of lipid synthesis. Glycolysis and the pentose phosphate pathway (pentosePP) are interconnected via fructose-6-P and glyceral-dehyde-3-P. A high level of NADPH favors lipid synthesis via pentose phosphate shunt (pentosePP). At TPI inhibition (TPI deficiency), glyceraldehyde-3-Pcan be produced via G6PDH as well, to contribute to the glycolytic flux. a-GDH catalyzes the...

DHAP, a glycolysis intermediate, is reduced by NADH to glycerol-3-phosphate. Triose isomerase converts it to glyceraldehyde-3-phosphate, and it is a product of the fructose-1-phosphate aldolase reaction. 

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