The Glycolysis Pathway

Further steps in glycolysis use the D-glyceraldehyde 3-phosphate fonned in 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 glycolysis pathway for further transfonnations. 

One of the most striking features of the common fatty adds is that they have an even number of carbon atoms (Table 27.1, p. 1062). This even number results because all fatty acids are derived biosynthelically from acetyl CoA by sequential addition of two-carbon units to a growing chain. The acetyl CoA, in turn, arises primarily from the metabolic breakdown of carbohydrates in the glycolysis pathway that weTl see in Section 29.5. Thus, dietary carbohydrates consumed in excess of immediate energy needs are turned into fats for storage. 

The glycolysis pathway shown in Figure 29.7 has a number of intermediates that contain phosphate groups. Why can 3-phosphoglyceryl phosphate and phosphoenolpyruvate transfer a phosphate group to ADP while glucose 6-phosphalc cannot ... 

Figure 3.15 Histogram of number of enzymes of the glycolysis pathway (from multiple organs and species) with different values of [S J/A m under physiological conditions.

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. 

Phosphoenolpyruvate, a key metabolic intermediate. A compound of central importance in metabolism is the phosphate ester of the enol form of pyruvate, commonly known simply as phosphoenolpyruvate (PEP).249 It is formed in the glycolysis pathway by dehydration of 2-phosphoglycerate (Eq. 13-15) or by decarboxylation of oxaloacetate. Serving as a preformed enol from which a reactive enolate anion can be released for condensation reactions,250 251 PEP... 

Figure 17-7 Outline of the glycolysis pathway by which hexoses are broken down to pyruvate. The ten enzymes needed to convert D-glucose to pyruvate are numbered. The pathway from glycogen using glycogen phosphorylase is also included, as is the reduction of pyruvate to lactate (step 11). Steps 6a-7, which are involved in ATP synthesis via thioester and acyl phosphate intermediates, are emphasized. See also Figures 10-2 and 10-3, which contain some additional information.

In vivo, the D-fructose 1,6-bisphosphate aldolase (FruA EC 4.1.2.13) catalyzes the pivotal reaction of the glycolysis pathway the equilibrium addition of 41 to D-glyceraldehyde 3-phosphate (GA3P, 12) to give D-fructose 1,6-bisphosphate (42) [43]. The equilibrium constant of 104 M 1 strongly favors synthesis [229]. 

The production of ethanol uses the glycolysis pathway, a common biochemical pathway that is present in animals as well as in yeast and bacteria. In this pathway glucose is commonly converted to pyruvate when oxygen is present (aerobiosis), but if oxygen is lacking (anaerobiosis), ethanol is produced. 

Subsequent exposure of geminal dibromide 62 to BU3S11H provided the desired ester 63 via a stereocontrolled cyclization-debromination tandem sequence. Finally, Barbier-Wieland degradation and hydrogenolytic debenzylation of ester 63 afforded 5a-carba-D-fructofuranose 64 in excellent yields. In a preliminary enzymological study, its 6-phosphate derivative showed to be an interesting substrate for the enzymes of the glycolysis pathway. 

The glycolysis pathway is an intermediate metabolism pathway for glucose oxidation located in the cytosol. 

The next reaction in the glycolysis pathway is catalyzed by phosphoglucoi-somerase and involves the isomerization of glucose-6-phosphate into fructose-6-... 

Figure 18.2 The glycolysis pathway. The AGq values for each reaction are given in kilojoules. Enzymes subject to various regulatory factors are indicated by jagged boxes. (Reproduced by permission from Wills ED. Biochemical Basis of Medicine Bristol Wright, 1985, p. 584.)...

Many microorganisms recover the NAD+ that is necessary for a continuous operation of the glycolysis pathway by ethanol production from pyruvate. The reaction may be written as... 

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