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You are watching: Does glycolysis take place in the mitochondria

StatPearls . Sweetheart Island (FL): StatPearls Publishing; 2021 Jan-.


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Introduction

Through the process of glycolysis, one molecule of glucose breaks down to form two molecules of pyruvate. Relying on the microcellular atmosphere (specifically, oxygen availability, energy demand, and also the visibility or lack of mitochondria), pyruvate has several different fates:

In mitochondria-containing cells, pyruvate can get in the citric acid cycle in ~ the mitochondrial matrix and also undergo oxidative phosphorylation. Aptly named due to its dependence on oxygen as the final electron acceptor, oxidative phosphorylation can not take place in the absence of oxygen. Moreover, together the enzymes of both the citric mountain cycle and also electron deliver chain room within the mitochondria, cells lacking mitochondria (e.g., erythrocytes) cannot depend on oxidative phosphorylation for energy production.

In erythrocytes and also oxygen-deprived tissue, pyruvate continues to be within the cytoplasm and converts come lactate, a process referred to together anaerobic glycolysis. This last reaction enables for the rebirth of NAD+, a cofactor that should be easily accessible in high sufficient intracellular concentrations for the earlier reactions that glycolysis to remain favorable. Compared to oxidative phosphorylation, however, anaerobic glycolysis is considerably less efficient, offering a net manufacturing of just 2 ATP every glucose molecule (versus 32 ATP every glucose molecule created during oxidative phosphorylation).<1>


Fundamentals

Glycolysis is the procedure by which glucose is broken down within the cytoplasm that a cell to type pyruvate. Under aerobic conditions, pyruvate have the right to diffuse right into mitochondria, whereby it enters the citric mountain cycle and also generates reducing equivalents in the form of NADH and FADH2. This reducing equivalents then enter the electron transport chain, resulting in the production of 32 ATP per molecule that glucose. Due to the fact that the electron carry chain requires oxygen as the final electron acceptor, inadequate tissue oxygenation inhibits the process of oxidative phosphorylation.

Under anaerobic conditions, pyruvate has actually a different fate. Instead of entering mitochondria, the cytosolic enzyme lactate dehydrogenase counter pyruvate come lactate. Although lactate chin is not used by the cell as a direct energy source, this reaction also allows for the renewal of NAD+ from NADH. NAD+ is one oxidizing cofactor important to maintain the flow of glucose v glycolysis. Glycolysis produce 2 ATP every glucose molecule, and thus gives a direct way of creating energy in the absence of oxygen. This process of breaking down glucose in the absence of oxygen is aptly named anaerobic glycolysis.<1>

Additionally, cells that perform not save on computer mitochondria (e.g., erythrocytes) cannot carry out oxidative phosphorylation.<2> The enzyme of the citric acid cycle room in the mitochondrial matrix, and also the enzyme of the electron deliver chain are installed within the inside mitochondrial membrane. Consequently, these cells rely on anaerobic glycolysis for ATP manufacturing regardless of oxygen concentrations.


Issues that Concern

Relative to oxidative phosphorylation, which maximizes the energy potential of a single glucose molecule (approximately 32 molecules of ATP every 1 molecule the glucose), glycolysis is an inefficient method of energy production. Glycolysis produces only two network molecules of ATP per 1 molecule that glucose. However, in cells doing not have mitochondria and/or sufficient oxygen supply, glycolysis is the sole process by which together cells can develop ATP indigenous glucose. Additionally, in maximally contracted skeletal muscle, glycolysis is a rapid and relatively efficient means of meeting short-term energy goals.


Function

Anaerobic glycolysis serves together a method of energy production in cells the cannot create adequate energy through oxidative phosphorylation. In poorly oxygenated tissue, glycolysis produce 2 ATP by shunting pyruvate away from mitochondria and also through the lactate dehydrogenase reaction.<1> In rapidly contracting bones muscle cells v energy demand exceeding what deserve to be developed by oxidative phosphorylation alone, anaerobic glycolysis enables for the much more rapid production of ATP.<3> (Glycolysis is roughly 100 times much faster than oxidative phosphorylation.) In cells lacking mitochondria altogether, pyruvate can not undergo oxidative phosphorylation nevertheless of oxygen levels.

Mature erythrocytes carry out not save mitochondria and thus rely solely on anaerobic glycolysis for ATP production.<2> various other tissues, such together the cornea and lens the the eye and also inner medulla the the kidney, room poorly vascularized and rely greatly on anaerobic glycolysis regardless of the visibility of mitochondria.<4><5>


Glucose it s okay phosphorylated by hexokinase, forming glucose-6-phosphate. This step calls for one molecule that ATP.
Fructose-6-phosphate is phosphorylated by phosphofructokinase to form fructose-1,6-bisphosphate. This step requires one molecule the ATP.
Fructose-1,6-bisphosphate is separation into two different sugar molecules, dihydroxyacetone phosphate and also glyceraldehyde-3-phosphate, by aldolase.
The molecule of dihydroxyacetone phosphate is isomerized by triosephosphate isomerase to form a second glyceraldehyde-3-phosphate.
Glyceraldehyde-3-phosphate is phosphorylated by glyceraldehyde-3-phosphate dehydrogenase to kind 1,3-bisphosphoglycerate. This step needs NAD+ as a cofactor.
1,3-bisphosphoglycerate is converted to 3-phosphoglycerate through phosphoglycerate kinase. This step entails the transport of a phosphate molecule come ADP to form 1 molecule the ATP.
Phosphoenolpyruvate is converted to pyruvate by pyruvate kinase. This step requires the deliver of a phosphate molecule to ADP to form 1 molecule of ATP.

The microenvironment of the cell determines the fate the pyruvate following the early stage ten measures of glycolysis. If a cell lacks mitochondria, is poorly oxygenated, or energy need has rapidly increased to exceed the price at i beg your pardon oxidative phosphorylation can provide sufficient ATP, pyruvate can be convert to lactate through the enzyme lactate dehydrogenase.<1> This step involves the oxidation that NADH to NAD+, allowing glycolysis to continue through the glyceraldehyde-3-phosphate dehydrogenase reaction (step #6, see above).

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Testing

Lactic acid, the finish product of anaerobic glycolysis, is commonly measured in the inpatient setting. Because anaerobic glycolysis predominates as soon as tissue is poorly oxygenated or perfused, lactic acid levels are valuable in directing the monitoring of severe sepsis, shock, blood loss, anemia, or heart failure. Hyperlactatemia and also lactic acidosis are indicative that inefficient cardiac output and are associated with raised morbidity and mortality.<6><7><8>