What is the glycolysis stage
Glycolysis (Greek glycos"cute" and lysis "Cleavage"), Embden-Meyerhof-Parnas-Weg, an essential metabolic pathway for all organisms for the catabolic breakdown of glucose with the formation of adenosine triphosphate (ATP). In the narrower sense, it is understood to be the anaerobic G., d. H. the breakdown of glucose without the participation of oxygen to lactate (salt of lactic acid) or ethanol (alcoholic fermentation). This way of anaerobic utilization of glucose is the oldest biochemical mechanism for the production of energy in the form of ATP, which enabled the development of living organisms in an oxygen-free atmosphere. The anaerobic G. is the most important way of obtaining ATP for various anaerobic and facultative anaerobic microorganisms. 150.72 kJ (36 kcal) of energy are obtained from each molecule of converted glucose, which is used for the net synthesis of 2 molecules of adenosine triphosphate. Under aerobic conditions ("aerobic" G.), while almost all reaction steps are retained, pyruvate (salt of pyruvic acid) is an intermediate which is then produced by the pyruvate dehydrogenase complex under CO2-Deaction and oxidation to acetyl-CoA reacts further. After joining the tricarboxylic acid cycle, the acetyl radical becomes CO2 degraded, and the reduction equivalents formed lead to a significantly higher energy yield in the respiratory chain.
The G. up to the stage of pyruvate (Fig. 1, Tab.) Is catalyzed by 10 cytosolic enzymes. In the preparatory phase, the consumption of ATP leads to the formation of fructose-1,6-diphosphate, which is then split into 2 molecules of triose phosphate. The 2 molecules of glyceraldehyde-3-phosphate, ultimately formed from glucose, are then oxidized at C-1, with the energy gained in the form of reduction equivalents (NADH + H+) and 1,3-diphosphoglycerate is preserved (Fig. 2). This intermediate has a high phosphate group transfer potential and, under the catalysis of phosphoglycerate kinase, enables the transfer of the phosphate residue to ADP with the formation of ATP (substrate chain phosphorylation). After the formation of phosphoenolpyruvate, the second substrate chain phosphorylation of G. provides another equivalent of ATP with the generation of pyruvate. The NADH + H formed in the reaction of glyceraldehyde-3-phosphate dehydrogenase+ needs to be regenerated. While under anaerobic conditions many organisms use the electrons of the NADH + H+ When transferred to pyruvate with the formation of lactate (Fig. 3), NAD is regenerated+ in the mitochondria in the process of breathing. In the vertebrate muscle, too, intensive muscle activity leads to lactate formation when there is insufficient oxygen supply. Balance:
Glucose (C.6H12O6) + 2Pi + 2ADP → 2lactate (C.3H6O3) + 2ATP.
Yeast cells regenerate NAD+ by reducing pyruvate to ethanol and CO2. These anaerobic processes are known as fermentation or fermentation.
The key enzyme in glycolysis is 6-phosphofructo-kinase (EC 188.8.131.52), which is inhibited by high concentrations of ATP and activated by ADP and AMP. Their product, fructose diphosphate, activates pyruvate kinase. The Pasteur effect is another form of regulation of glycolysis.
Fig. 2. Glycolysis. Mechanism of reactions 8 and 10 of glycolysis (see table). enzyme1 = Triose phosphate dehydrogenase, enzyme2 = Phosphoglyceromutase.
Fig. 3. Glycolysis. Oxidoreduction cycle of glycolysis.
Tab. Glycolysis. Glycolysis reactions.
|1||Starch or glycogen + nPi → n-glucose-1-P|| Phosphorylase|
|2||Glucose-1-P → glucose-6-P|| Phosphoglucomutase|
|Fluoride, organic phosphates|| -7,29|
|3||Glucose + ATP → glucose-6-P + ADP|| Hexokinase |
|4|| Glucose-6-P |
| Glucose phosphate isomerase|
|5|| Fructose-6-P + ATP → fructose-1,6-P2 +|
ADP + H+
| 6-phosphofructo kinase|
|ATP, citrate|| -14,24|
| Fructose diphosphate aldolase|
|Chelating agents (only for enzymes from microorganisms)|| +24,01|
|7|| Dihydroxyacetone-P |
| Triose phosphate isomerase|
|8|| Glyceraldehyde-3-P + Pi + NAD+|
1,3-P2-Glycerate + NADH + H+
| Glyceraldehyde phosphate|
|9|| 1,3-P2-Glycerate + ADP + H+|
3-P-glycerate + ATP
| Phosphoglycerate kinase|
|10|| 3-P-glycerate |
| Phosphoglycero mutase|
|11|| 2-P-glycerate |
|Approx2+, Fluorine + Pi|| +1,84|
|12|| Phosphoenolpyruvate + ADP + H+|
Pyruvate + ATP
| Pyruvate kinase|
|Approx2+, N / A+|| -31,44|
|13|| Pyruvate + NADH + H+|
Lactate + NAD+
| Lactate dehydrogenase|
Note: Reactions 8 to 13 must be doubled in the course of the glycolysis, since both trioses (reactions 6 and 7) are converted. P = phosphate, Pi = inorganic phosphate.
Fig. 1. Glycolysis. Overview. a) First stage (preparatory stage): phosphorylation of glucose and its conversion into glyceraldehyde-3-phosphate. b) Second level (yield level): Conversion of glyceraldehyde-3-phosphate into pyruvate and the associated ATP formation.
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