Glycolysis substrate-level phosphorylation

The total number of ATP produced by glycolysis and metabolism is 38 molecules, which includes a net of two from glycolysis (substrate level phosphorylation), 30 from the oxidation of 10 NADH molecules, four from oxidation of two FADH2 molecules, and two from substrate level phosphorylation in the Krebs cycle. 

Whereas ATP made in glycolysis and the TCA cycle is the result of substrate-level phosphorylation, NADH-dependent ATP synthesis is the result of oxidative phosphorylation. Electrons stored in the form of the reduced coenzymes, NADH or [FADHa], are passed through an elaborate and highly orga-... 

Examples of substrate level phosphorylation are to be found in glycolysis. Phos-phoglycerate kinase (PGK) and pyruvate kinase (PK) catalyse the following reactions ... 

In contrast to substrate level phosphorylation in glycolysis, mitochondrial oxidative phosphorylation is an efficient process in that it generates in excess of 30 ATP per mole of glucose. In essence, the movement of electrons along the respiratory chain or electron transport chain is coupled with phosphorylation of ADP. 

The loss of AMP especially in active muscles is partly ameliorated by recycling of IMP via adenylosuccinate. Furthermore, because AMP is an important allosteric activator of PFK, regeneration of AMP ensures that glycolysis is fully active and able to provide pyruvate for the TCA cycle and some ATP via substrate level phosphorylation. 

Pyruvate kinase the last enzyme in aerobic glycolysis, it catalyzes a substrate-level phosphorylation of ADP using the high-energy substrate phosphoenolpyruvate (PEP). Pyruvate kinase is activated by fructose 1,6-bisphosphate from the PFK-1 reaction (feedforward activation). 

Figure 6-1. The steps of glycolysis. Feedback inhibition of glucose phosphorylation by hexokinase, inhibition of pyruvate kinase, and the main regulatory, rate-limiting step catalyzed by phosphofructoki-nase (PFK-I) are indicated, pyruvate formation and substrate-level phosphorylation are the main outcomes of these reactions. Regeneration of NAD occurs by reduction of pyruvate to lactate during anaerobic glycolysis.

Figure 23-2. Metabolism in the fed state. An adequate supply of carbohydrate provides glucose to replenish glycogen stores. Dietary protein provides amino acids for protein synthesis. Dietary carbohydrates, fats, and proteins can all be metabolized to generate ATP. (For clarity, ATP generation during P-oxidation of fatty acids and substrate-level phosphorylation during glycolysis is not depicted.) Excess dietary carbohydrates and amino acids are converted to fatty acids and, along with excess dietary fatty acids, stored as triacylglycerols. DHAP, dihydroxyacetone phosphate.

When grown under aerobic conditions, the yeast produces two ATP molecules from one molecule of glucose by substrate-level phosphorylation in glycolysis. The two molecules of pyruvate produced can then be completely oxidized to CO2, and each yields a further 15 molecules of ATP. This leads to a slow decrease in the concentration of glucose, a steady production of CO2, and relatively little change in the amount of ATP. Also, the two molecules of NADH can be reoxidized to NAD+ by the electron-transport system. (This produces yet more ATP, as discussed in Chap. 14.)... 

Which of the following could theoretically yield the maximum net number of molecules of ATP by substrate-level phosphorylation in glycolysis a molecule of sucrose, two molecules of glucose, or two molecules of fructose ... 

If a molecule of glucose produces two molecules of ATP by substrate-level phosphorylation of ADP in glycolysis and the resulting two molecules of pyruvate can each yield 15 molecules of ATP when oxygen is available, how many glucose molecules will be necessary to produce 160 molecules of ATP by yeast grown under (a) aerobic and (6) anaerobic conditions ... 

LAB are non-respiring microorganisms, principally generating ATP by fermentation of carbohydrates coupled to substrate-level phosphorylation. The two major pathways for the metabolism of hexoses are homofermentative or glycolysis (Embden-Meyerhof pathway), in which lactic acid is virtually the only end-product, and heterofermentative (phosphoketolase pathway), in which other end-products such as acetic acid, C02, and ethanol are produced in addition to lactic acid (Axelsson et al., 1989 Kandler, 1983 Zourari et al., 1992). 

ATP is synthesized from ADP and phosphate during electron transport in the respiratory chain. This type of phosphorylation is distinguished from substrate-level phosphorylation, which occurs as an integral part of specific reactions in glycolysis and the TCA cycle. The free energy available for the synthesis of ATP during electron transfer from NADH to oxygen can be calculated from the difference in the value of the standard potential of the electron donor system and that of the electron acceptor system. The standard potential of the NADH/NAD+ redox component is —0.32 V and that of H2O/5O2 is -1-0.82 V therefore, the standard potential difference between them is... 

Cellular adenine nucleotides are compartmentalized by their very low diffusibility (due to their size and charge) with pools in the mitochondria, at the myofibrils, SR, and other sites of energy utilization. CK is located at those sites. Phosphocreatine is much smaller and less charged, and therefore much more mobile in cells than ATP. ATP produced by substrate-level phosphorylation in glycolysis may be used to rephosphorylate creatine in the sarcoplasm ... 

The answer is f. (Murray, pp 182-189. Scriver, pp 2367-2424. Sack, pp 159—175. Wilson, pp 287-317.) In contrast to the case with glycolysis, the only site of substrate-level phosphorylation in the tricarboxylic acid cycle... 

Define substrate-level phosphorylation. Which two reactions in glycolysis are in this category ... 

Four molecules of ATP are formed from ADP during glycolysis via substrate-level phosphorylation, which is catalyzed by enzymes in the cytosol (reactions 7 and 10). Unlike ATP formation in mitochondria and chloroplasts, a proton-motive force is not involved in substrate-level phosphorylation. Early In the glycolytic pathway, two ATP molecules are consumed one by the addition of a phosphate residue to glucose In the reaction catalyzed by hex okinase (reaction 1), and another by the addition of a second phosphate to fructose 6-phosphate In the reaction catalyzed by phosphofructokinase 1 (reaction 3). Thus glycolysis yields a net of only two ATP molecules per glucose molecule. 

The hypothesis that a proton-motive force across the inner mitochondrial membrane is the immediate source of energy for ATP synthesis was proposed in 1961 by Peter Mitchell. Virtually all researchers working in oxidative phosphorylation and photosynthesis Initially opposed this chemlosmotic mechanism. They favored a mechanism similar to the well-elucidated substrate-level phosphorylation in glycolysis, in which oxidation of a substrate molecule is directly coupled to ATP synthesis. By analogy, electron transport through the... 

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