What is Glycolysis?
Glycolysis converts glucose into energy in the form of NADH, ATP and Pyruvate. In the presence or absence of oxygen, the site of glycolysis in a cell is in the cytosol of a cell’s cytoplasm. The first stage in cellular respiration is glycolysis. In the absence of oxygen, cells use the fermentation process to obtain modest quantities of ATP. The EMP route (Embden–Meyerhof–Parnas) was identified by three Jakub Karol Parnas, Otto Meyerhof, Gustav Embden and German biochemists, in the early nineteenth century.
Anaerobic glycolysis
When just a little amount of oxygen (O2) is available, anaerobic glycolysis is used to convert glucose to lactate. Anaerobic glycolysis is only useful for producing energy during brief bouts of high-intensity activity, lasting between 10 and 2 minutes. This is far more rapid than aerobic metabolism.
Aerobic glycolysis
The word “aerobic glycolysis” refers to a set of events in which oxygen is required to reoxidize NADH to NAD+. This ten-step procedure starts with a molecule of glucose and concludes with two pyruvate molecules.
Glycolysis Pathway
Following are the ten steps of the glycolysis pathway.
Step 1: When a molecule of glucose enters the cell, it is instantly phosphorylated to glucose-6-phosphate by the enzyme hexokinase, which uses the phosphate released during ATP hydrolysis. The glucose molecule is trapped within the cell by this irreversible action. Hexokinase can phosphorylate any six-carbon sugars, including glucose, and has a wide specificity. Glucokinase has an isozyme form that only phosphorylates glucose in the liver and pancreatic beta cells.
Step 2: Phosphoglucose isomerase is responsible for the conversion of glucose-6-phosphate (aldose) to fructose-6-phosphate (ketose). This is a simple reversible reaction.
Step 3: By using the enzyme phosphofructokinase-1, fructose-6-phosphate is phosphorylated to fructose-1, 6-bisphosphate (PFK1). This is a regulatory action that is both irreversible and rate-limiting. In glycolysis, this committed step consumes the second most ATP.
Step 4: In this uncontrolled, reversible process, the enzyme aldolase cleaves fructose-1, 6-bisphosphate to produce dihydroxyacetone phosphate (DHAP) and glyceraldehyde-3-phosphate (G3P). In addition to fructose-1, 6-bisphosphate, Aldolase B, an isomer version of the enzyme found in the liver, cleaves fructose-1-phosphate (in fructose metabolism).
Step 5: Triosephosphate isomerase is responsible for the interconversion of DHAP and glyceraldehyde-3-phosphate. Two molecules of glyceraldehyde-3-phosphate are formed as a result of this isomerisation.
Step 6: Glyceraldehyde-3-phosphate dehydrogenase catalyzes the oxidation of glyceraldehyde-3-phosphate, resulting in 1, 3-bisphosphoglycerate production. The aldehyde group of glyceraldehyde -3-phosphate is oxidised to a carboxyl group connected to the attachment of a phosphate group in the first oxidation-reduction phase of glycolysis, where NAD+ is reduced to NADH and the aldehyde group of glyceraldehyde -3-phosphate is oxidised to a carboxyl group. Because cells have a limited amount of NAD+, they must be reoxidized to NADH. NADH is reoxidised to NAD+ in the mitochondria under aerobic circumstances, whereas lactate dehydrogenase regenerates it in anaerobic ones.
Step 7: In glycolysis, the first ATP-generating step is the formation of 3-phosphoglycerate from 1,3-bisphosphoglycerate (1,3-BPG). With the help of phosphoglycerate kinase, the phosphate group attached during the formation of 1,3-BPG in the previous step is used to phosphorylate ADP, resulting in ATP. The phosphorylation of the substrate yields two ATPs. Bisphosphoglycerate mutase converts some of the 1,3-BPG into 2,3-bisphosphoglycerate (2,3-BPG), a key component that aids oxygen supply to cells. 2,3-BPG is normally present in negligible amounts, however during hypoxic circumstances, its synthesis will rise.
Step 8: Phosphoglycerate mutase next performs a reversible isomerisation conversion of 3-phosphoglycerate to 2-phosphoglycerate, in which the phosphate group of phosphoglycerate is moved from the third to the second carbon.
Step 9: Phosphoenolpyruvate, which includes the high-energy enol phosphate, is formed from 2-phosphoglycerate.
Step 10: Pyruvate kinase converts phosphoenolpyruvate to pyruvate, which is the final step in glycolysis. This irreversible process generates two molecules of ATP via phosphorylation at the substrate level.
Pyruvate can then go to the mitochondria through an aerobic or anaerobic pathway, forming lactic acid. Glycolysis produces a net gain of two molecules of ATP per molecule of glucose, regardless of the path (aerobic or anaerobic) taken.
Key Points of Glycolysis
- It’s the process of breaking down a molecule of glucose into two pyruvate molecules
- In the cytoplasm of plant and animal cells, the process takes place
- The process is carried out by six enzymes
- Two pyruvate, two ATP, and two NADH molecules are the reaction’s end products