Overview of Glycolysis

The process of glycolysis is without a doubt the single most ubiquitous pathway in all energy metabolism. Glycolysis can be characterized as a nearly universal process because it occurs in almost every living cell. It can occur in the ab- 

The glycolytic pathway was the first major metabolic sequence to be elucidated. Much of the definitive work was done in the 1930s by the German biochemists, Gustav Embden, Otto Meyerhof, and Otto Warburg. Because of their contributions the alternative name, Embden-Meyerhof pathway, is sometimes used for the glycolytic pathway. 

Structure of the helical complex of amylose with iodine (I2). The amylose forms a left-handed helix with six glucosyl residues per turn and a pitch of 0.8 nm. The iodine molecules (I2) fit inside the helix parallel to its long axis. 

Except for glycerate-l,3-bisphosphate all of the intermediates in the pathway are pictured as belonging to one of three metabolic pools. Within each metabolic pool the intermediates are readily interconvertible and usually present in relative concentrations close to their equilibrium values. Between the pools the concentrations of the intermediates can be very different because of the lack of rapid intercon- 

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In the overview of glycolysis we noted that the pyruvate produced must be used up in some way so that the pathway will continue to produce ATP. Similarly, the NADH produced by glycolysis in step 6 (see Figure 21.8) must be reoxidized at a later time, or glycolysis will grind to a halt as the available NAD+ is used up. If the cell is functioning under aerobic conditions, NADH will be reoxidized, and pyruvate will be completely oxidized by aerobic respiration. Under anaerobic conditions, however, different types of fermentation reactions accomplish these purposes. Fermentations are catabolic reactions that occur with no net oxidation. Pyruvate or an organic compound produced from pyruvate is reduced as NADH is oxidized. We will examine two types of fermentation pathways in detail lactate fermentation and alcohol fermentation. 

We will return to an overview of anabolic pathways shortly, but first we want to examine in more detail the two important catabolic pathways, glycolysis and the tricarboxylic acid cycle. 

During ripening, three primary biochemical events occur, glycolysis, lipolysis and proteolysis. The products of these primary reactions undergo numerous modifications and interactions. The primary reactions are fairly well characterized but the secondary changes in most varieties are more or less unknown. An overview of the principal biochemical changes follows. 

FIGURE 22-9 Overview of amino acid biosynthesis. The carbon skeleton precursors derive from three sources glycolysis (pink), the citric acid cycle (blue), and the pentose phosphate pathway (purple). 

Chemically induced cardiac failure has been the subject of a number of works. Balazs and Ferrans (1978), Baskin (1991), and Acosta (2001) give an overview of the subject. Hypoxia is one of the effects of the decreased availability of ATP which depresses contraction in the muscle. The energy that is supplied by the phosphate bonds is possible only as long as aerobic glycolysis and oxidative phosphorylation are maintained. Under anoxic conditions, this is no longer possible and with the adrenergic stimulus continuing, calcium accumulation in the mitochondria leads to... 

Conceptual Insights, Overview of Carbohydrate and Fatty Acid Metabolism. View this media module to gain a "bigger picture" understanding of the roles of the pentose phosphate pathway in the context of other metabolic pathways (glycolysis, citric acid cycle, glycogen and fatty acid metabolism). 

Figure 7-6. Overview of the synthesis of nonessential amino adds. Ten amino acids may be produced from glucose via intermediates of glycolysis or the TCA cycle. The eleventh amino acid, tyrosine, is synthesized by hydroxylation of the essential amino acid phenylalanine. TA = transamination GDH- glutamate dehydrogenase.

If the cell requires more NADPH than ribose molecules, it can channel the products of the nonoxidative phase of the pentose phosphate pathway into glycolysis. As this overview of the two pathways illustrates, excess ribose-5-phos-phate can be converted into the glycolytic intermediates fructose-6-phosphate and glyceraldehyde-3-phosphate. 

Next step of glycolysis Enzymes of glycolysis Glycolysis overview... 

Genetic Disorders of Glycolysis An Overview Reactions of Glycolysis Regulation of Glycolysis... 

Fig. 29.2. Overview of the pentose phosphate pathway. The pentose phosphate pathway generates NADPH for reactions requiring reducing equivalents (electrons) or ribose 5-phosphate for nucleotide biosynthesis. Glucose 6-phosphate is a substrate for both the pentose phosphate pathway and glycolysis. The 5-carbon sugar intermediates of the pentose phosphate pathway are reversibly interconverted to intermediates of glycolysis. The portion of glycolysis that is not part of the pentose phosphate pathway is shown in blue.

Goenzymes are introduced in this chapter and are discussed in later chapters in the context of the reactions in which they play a role. Chapter 16 discusses carbohydrates. Chapter 17 begins the overview of the metabohc pathways by discussing glycolysis. Glycogen metabolism, gluconeogenesis, and the pentose phosphate pathway (Chapter 18) provide bases for treating control mechanisms in carbohydrate metabolism. Discussion of the citric acid cycle is followed by the electron transport chain and oxidative phosphorylation in Chapters 19 and 20. The catabolic and anabolic aspects of lipid metabohsm are dealt with in Chapter 21. In Chapter 22, photosynthesis rounds out the discussion of carbohydrate metabolism. Chapter... 

Fig. 11-4 Overview of giucose uptake and disposal in skeletal myocytes and adipocytes. Giucose enters the ceil via GLUT-1 and via the insulin-stimulated insertion of GLUT-4 carriers into the plasma membrane. Glucose 6-phosphate is a point of flux divergence into glycolysis and glycogen synthesis.

Systems of biochemical reactions like glycolysis, the citric acid cycle, and larger and smaller sequential and cyclic sets of enzyme-catalyzed reactions present challenges to make calculations and to obtain an overview. The calculations of equilibrium compositions for these systems of reactions are different from equilibrium calculations on chemical reactions because additional constraints, which arise from the enzyme mechanisms, must be taken into account. These additional constraints are taken into account when the stoichiometric number matrix is used in the equilibrium calculation via the program equcalcrx, but they must be explicitly written out when the conservation matrix is used with the program equcalcc. The stoichiometric number matrix for a system of reactions can also be used to calculate net reactions and pathways. 

Overview Glycolysis is a series of reactions (Fig. 1) that takes place in the cytoplasm of... 

Despite the enormous variety of SM, the number of corresponding basic bios)mthetic pathways is restricted and distinct. Precursors usually derive from basic metabolic pathways, such as glycolysis, the Krebs cycle or the shikimate pathway A schematic overview is presented in Figs 1.2 and 1.3. Plausible hypotheses for the bios)mthesis of most SM have been published (for overviews see Bell and Charlwood, 1980 Conn, 1981 Mothes et al,... 

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