Glucose to Pyruvate

Tracing labeled carbon atoms through metabolic pathways would, at first glance, appear to be a pretty irrelevant thing to make you do. But if you ve got to do it, there are a couple of conceptual tricks that make it somewhat easier. 

The first concept is that organic compounds are numbered starting with the end of the molecule that is closest to the most oxidized carbon. 

Labeling a given molecule at a specific carbon atom means that an 

Tracing the carbons of glucose to pyruvate gets complicated when fructose 1,6-bisphosphate (FBP) is cleaved into two 3-carbon fragments, glyceraldehyde 3-phosphate (G3P) and dihydroxyacetone phosphate (DHAP). The numbers of the original carbons of glucose are indicated by the superscripts next to the carbon. 

The guilty party is the triose phosphate isomerase (TIM) reaction that interconverts DHAP and G3P. To be converted to pyruvate, the DHAP first has to be converted to G3P. TIM just moves the carbonyl group between the two carbons that don t have phosphate attached. TIM doesn t touch the phosphate. So, if the DHAP is labeled at the carbon that has the phosphate attached, the G3P that comes from DHAP will be labeled at the carbon with the phosphate attached. The carbon with the phosphate attached in the G3P that was produced directly by the aldolase reaction came from C-6 of glucose, but the carbon with the phosphate attached in the G3P that was produced from DHAP came from C-1 of glucose. After TIM does it stuff, the carbon of G3P that has the phosphate will be 

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Figure 6.24 The function of the enzyme phosphofructokinase. (a) Phosphofructokinase is a key enzyme in the gycolytic pathway, the breakdown of glucose to pyruvate. One of the end products in this pathway, phosphoenolpyruvate, is an allosteric feedback inhibitor to this enzyme and ADP is an activator, (b) Phosphofructokinase catalyzes the phosphorylation by ATP of fructose-6-phosphate to give fructose-1,6-bisphosphate. (c) Phosphoglycolate, which has a structure similar to phosphoenolpyruvate, is also an inhibitor of the enzyme.

Glycolysis glucose to pyruvate (cytosol) Phosphorylation of glucose -1 -1... 

Take glycolysis, for example, the metabolic pathway by which organisms convert glucose to pyruvate as the first step in extracting energy from carbohydrates. 

While glycolysis degrades glucose to pyruvate and NADH, the pentose shunt leads from glucose to pentose and NADPH. 

Aerobic To convert glucose to pyruvate and ATP. Pyruvate can be burned for energy (TCA) or converted to fat (fatty acid synthesis). 

Glycolysis the metabolic pathway leading from glucose to pyruvate and lactate. 

For each molecule of glucose degraded to pyruvate, two molecules of ATP are generated from ADP and Pj. We can now resolve the equation of glycolysis into two processes—the conversion of glucose to pyruvate, which is exergonic ... 

For each molecule of glucose formed from pyruvate, six high-energy phosphate groups are required, four from ATP and two from GTP. In addition, two molecules of NADH are required for the reduction of two molecules of 1,3-bisphosphoglycerate. Clearly, Equation 14-9 is not simply the reverse of the equation for conversion of glucose to pyruvate by glycolysis, which requires only two molecules of ATP ... 

If glycolysis (the conversion of glucose to pyruvate) and gluconeogenesis (the conversion of pyruvate to glucose) were allowed to proceed simultaneously at high rates,... 

The conversion of glucose to pyruvate occurs in two stages (Figure 8.11). The first five reactions of glycolysis correspond to an energy investment phase in which the phosphorylated forms of intermediates are synthe-... 

Formation of pyruvate. The conversion of glucose to pyruvate requires ten enzymes (Fig. 17-7), and the sequence can be divided into four stages preparation for chain cleavage (reactions 1-3), cleavage and equilibration of triose phosphates (reactions 4 and 5), oxidative generation of ATP (reactions 6 and 7), and conversion of 3-phosphoglycerate to pyruvate (reactions 8-10). 

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.

Glycolysis, the anaerobic degradation of glucose to pyruvate, generates ATP (equation 10.16). The glycolytic pathway is regulated to meet the cellular requirements for this important energy source. 

Three types of enzyme clustering are found (fig. 11.3). In the simplest situation, all of the catalytic activities for a particular pathway are found in proteins that exist as independent soluble proteins in the same cellular compartment. In such cases the intermediates must get from one enzyme to the next in the sequence by free diffusion through the cytosol or by transfer after contact between two sequentially related enzymes—one carrying the reactive intermediate and the other ready to receive it. Such is the situation for the enzymes involved in the breakdown of glucose to pyruvate. 

The breakdown of glucose to pyruvate. The conversion of glucose to pyruvate requires ten steps and one enzyme for each step. In steps 1 and 3, ATP is consumed. In steps 7 and 10, ATP is produced. The net production of ATP is 2 moles for each mole of glucose consumed. Unlike the intermediates in the tryptophan pathway, many of the intermediates between glucose and pyruvate serve as useful substances for other purposes. A full description of all the steps in this sequence is given in chapter 12. 

In analyzing metabolism we must distinguish between a sequence and a conversion. A conversion might be the transformation of starting material A to end product Z a sequence is the specific set of reactions by which such a conversion is carried out. The conversion of glucose to pyruvate involves a ten-step sequence (see figures 11.2 and... 

Using only figure 11.2 determine if the conversion of glucose to pyruvic acid is an oxidation or a reduction or neither. 

The glycolytic pathway from glucose to pyruvate, indicating two anaerobic options (ethanol or lactate) and one aerobic option (TCA cycle). The red arrow indicates how NADH formed in glycolysis... 

The components of respiratory metabolism include glycolysis, the tricarboxylic acid (TCA) cycle, the electron-transport chain, and the oxidative phosphorylation of ADP to ATP. Glycolysis converts glucose to pyruvate the TCA cycle fully oxidizes the pyruvate (by means of acetyl-CoA) to C02 by transferring electrons stepwise to... 

I n the previous two chapters, we described the catabolism of glucose to pyruvate by glycolysis and the further breakdown of pyruvate to C02 and H20 in the TCA cycle. These are oxidative processes. As the carbohydrate chain is chopped into progressively smaller fragments, electrons are... 

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