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You are watching: Does glycolysis occur in the mitochondria

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


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Introduction

Through the process of glycolysis, one molecule the glucose breaks under to type two molecules of pyruvate. Depending upon the microcellular setting (specifically, oxygen availability, energy demand, and the presence or lack of mitochondria), pyruvate has several different fates:

In mitochondria-containing cells, pyruvate can go into the citric acid cycle in ~ the mitochondrial matrix and also undergo oxidative phosphorylation. Aptly named because of its dependency on oxygen together 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 transport chain space within the mitochondria, cells lacking mitochondria (e.g., erythrocytes) cannot depend on oxidative phosphorylation for energy production.

In erythrocytes and oxygen-deprived tissue, pyruvate stays within the cytoplasm and converts come lactate, a process referred to as anaerobic glycolysis. This final reaction permits for the rebirth of NAD+, a cofactor that must be accessible in high sufficient intracellular concentrations because that the earlier reactions the glycolysis to continue to be favorable. Contrasted to oxidative phosphorylation, however, anaerobic glycolysis is substantially less efficient, offering a net manufacturing of only 2 ATP every glucose molecule (versus 32 ATP every glucose molecule created during oxidative phosphorylation).<1>


Fundamentals

Glycolysis is the process by which glucose is broken down within the cytoplasm that a cabinet to form pyruvate. Under aerobic conditions, pyruvate can diffuse right into mitochondria, whereby it enters the citric acid cycle and also generates to reduce equivalents in the kind of NADH and also FADH2. These reducing equivalents then go into the electron move chain, causing the manufacturing of 32 ATP per molecule that glucose. Because the electron deliver chain requires oxygen together the last electron acceptor, inadequate tissue oxygenation inhibits the process of oxidative phosphorylation.

Under anaerobic conditions, pyruvate has actually a various fate. Instead of start mitochondria, the cytosolic enzyme lactate dehydrogenase switch pyruvate to lactate. Back lactate chin is not used by the cell as a straight energy source, this reaction also allows for the renewal of NAD+ native NADH. NAD+ is one oxidizing cofactor essential to maintain the flow of glucose v glycolysis. Glycolysis produces 2 ATP every glucose molecule, and thus provides a direct method of developing energy in the lack of oxygen. This procedure of breaking down glucose in the absence of oxygen is aptly named anaerobic glycolysis.<1>

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


Issues that Concern

Relative to oxidative phosphorylation, i m sorry maximizes the energy potential of a solitary glucose molecule (approximately 32 molecule of ATP every 1 molecule of glucose), glycolysis is an inefficient method of energy production. Glycolysis produces just two net molecules that ATP per 1 molecule of glucose. However, in cells lacking 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 quick and relatively efficient means of conference short-term power goals.


Function

Anaerobic glycolysis serves as a method of energy production in cells the cannot produce adequate power through oxidative phosphorylation. In poorly oxygenated tissue, glycolysis produce 2 ATP through shunting pyruvate far from mitochondria and through the lactate dehydrogenase reaction.<1> In rapidly contracting skeletal muscle cells v energy demand exceeding what can be produced by oxidative phosphorylation alone, anaerobic glycolysis permits for the more rapid production of ATP.<3> (Glycolysis is roughly 100 times much faster than oxidative phosphorylation.) In cells doing not have mitochondria altogether, pyruvate can not undergo oxidative phosphorylation regardless of oxygen levels.

Mature erythrocytes execute not save on computer mitochondria and also thus rely specifically on anaerobic glycolysis because that ATP production.<2> other tissues, such as the cornea and lens the the eye and inner medulla the the kidney, space poorly vascularized and also rely heavily on anaerobic glycolysis regardless of the presence of mitochondria.<4><5>


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

The microenvironment the the cabinet determines the fate that pyruvate following the early stage ten actions of glycolysis. If a cabinet lacks mitochondria, is poorly oxygenated, or energy demand has rapidly increased to exceed the rate at i m sorry oxidative phosphorylation can carry out sufficient ATP, pyruvate have the right to be converted to lactate by the enzyme lactate dehydrogenase.<1> This step involves the oxidation the NADH to NAD+, permitting glycolysis to proceed through the glyceraldehyde-3-phosphate dehydrogenase reaction (step #6, check out above).

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Testing

Lactic acid, the finish product the anaerobic glycolysis, is frequently measured in the inpatient setting. Due to the fact that anaerobic glycolysis predominates once tissue is poorly oxygenated or perfused, lactic mountain levels are beneficial in directing the monitoring of major sepsis, shock, blood loss, anemia, or heart failure. Hyperlactatemia and also lactic acidosis space indicative of inefficient cardiac output and are connected with raised morbidity and also mortality.<6><7><8>