Glycolysis glycolytic pathway

The glycolytic pathway described in this chapter begins with the breakdown of glucose, but other sugars, both simple and complex, can enter the cycle if they can be converted by appropriate enzymes to one of the intermediates of glycolysis. Figure 19.32 shows the mechanisms by which several simple metabolites can enter the glycolytic pathway. Fructose, for example, which is pro-... 

Fructose-6-phosphate generated in this way enters the glycolytic pathway directly in step 3, the second priming reaction. This is the principal means for channeling fructose into glycolysis in adipose tissue, which contains high levels of fructose. 

Most of the NADH used in electron transport is produced in the mitochondrial matrix space, an appropriate site because NADH is oxidized by Complex I on the matrix side of the inner membrane. Furthermore, the inner mitochondrial membrane is impermeable to NADH. Recall, however, that NADH is produced in glycolysis by glyceraldehyde-3-P dehydrogenase in the cytosol. If this NADH were not oxidized to regenerate NAD, the glycolytic pathway would cease to function due to NAD limitation. Eukaryotic cells have a number of shuttle systems that harvest the electrons of cytosolic NADH for delivery to mitochondria without actually transporting NADH across the inner membrane (Figures 21.33 and 21.34). 

The complete route of gluconeogenesis is shown in Figure 23.1, side by side with the glycolytic pathway. Gluconeogenesis employs three different reactions, catalyzed by three different enzymes, for the three steps of glycolysis that are... 

N/ JDPH is considerably greater than the need for ribose-5-phosphate. The next three steps thus return some of the five-carbon units to glyceraldehyde-3-phos-phate and fructose-6-phosphate, which can enter the glycolytic pathway. The advantage of this is that the cell has met its needs for N/VDPH and ribose-5-phosphate in a single pathway, yet at the same time it can return the excess carbon metabolites to glycolysis. 

Probably the most well-known pathway to exemplify the occurrence of complex dynamics in metabolic networks is the glycolytic pathway of yeast. Arguably one of the most modeled pathways ever, minimal models of yeast glycolysis were studied since the 1960s [94, 273, 305 308] and give rise to a rich spectrum of... 

The first reaction vi (Gx. ATP) describes the upper part of glycolysis, converting one (external) molecule of glucose (Gx) into two molecules of triosephosphate (TP), using two molecules of ATP. The second reaction v2 (TP, ADP) describes the synthesis of two molecules ATP from each molecule of TP. The third reaction v3 (ATP) describes a (lumped) overall ATP utilization. To obtain a minimal kinetic model for the glycolytic pathway, we adopt rate function similar to [96], using... 

We now turn to the metabolic fate of these sugars, fit most cells, the metabolic pathway responsible is termed glycolysis or the glycolytic pathway. The starting point for glycolysis is D-glucose. The end products of glycolysis... 

A central consequence of glycolysis is the production of limited quantities of ATP, the energy currency of the cell. Specifically, the sum total of the glycolytic pathway from D-glucose to lactate is ... 

The glycolytic pathway, or glycolysis, is a metabolic sequence in which glucose is broken down to pyruvic acid. The subsequent fate of pyruvate then depends upon whether or not the organism is aerobic or anaerobic Under aerobic conditions, pyruvate is oxidized via oxidative phosphorylation under anaerobic conditions, pyruvate is converted further into compounds such as lactate or ethanol, depending upon the organism. 

Scheme 9.5 Multi-step enzymatic process for 2 -deoxyribo-nucleoside production from glucose, acetaldehyde and a nucleobase through glycolysis, reverse reactions of 2 -deoxy-ribonucleoside degradation and ATP regeneration by the yeast glycolytic pathway recycling the phosphate generated by nucleoside phosphorylase.

This enzyme is called PFK-1 to distinguish it from a second enzyme (PFK-2) that catalyzes the formation of fructose 2,6-bisphosphate from fructose 6-phosphate in a separate pathway. The PFK-1 reaction is essentially irreversible under cellular conditions, and it is the first committed step in the glycolytic pathway glucose 6-phosphate and fructose 6-phosphate have other possible fates, but fructose 1,6-bisphosphate is targeted for glycolysis. 

Glycolysis Shortcut Suppose you discovered a mutant yeast whose glycolytic pathway was shorter because of the presence of a new enzyme catalyzing the reaction ... 

The reaction catalyzed by phosphofructokinase A. is activated by high concentrations of ATP and citrate. B. uses fructose 1-phosphate as substrate. C. is the regulated reaction of the glycolytic pathway. D. is near equilibrium in most tissues. E. is inhibited by fructose 2,6-bisphosphate. Correct answer = C. Phosphofructokinase is the pace-setting enzyme of glycolysis. It is inhibited by ATP and citrate, uses fructose 6-phosphate as substrate, and catalyzes a reaction that is far from equilibrium. The reaction is activated by fructose 2,6-bisphosphate. 

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