Glycolysis is present in most living organisms. It is the first step in cellular respiration. It is a glycolytic pathway, which leads to a partial breakdown of glucose to pyruvate. Glycolysis is the common pathway in both aerobic and anaerobic respiration.
Glycolysis process does not require oxygen. The omnipresence of this pathway shows that it is an ancient metabolic pathway and has evolved long ago. It is an important pathway to derive energy in the form of ATP both aerobically as well as anaerobically, which is required by all the cells to perform cellular functions. It is an important metabolic pathway.
- This pathway is utilized by all the cells and tissues to get energy, which is stored in the form of ATP and NADH.
- It occurs in both prokaryotes and eukaryotes.
- It is employed in both aerobic and anaerobic respiration.
- The process of glycolysis occurs in cytosol, so it is a very important process of energy generation for those organisms, who do not possess mitochondria.
- The end product of glycolysis is pyruvate, which is an intermediate of various other processes such as gluconeogenesis, fatty acid synthesis, fermentation, etc.
- Even intermediates of the glycolysis process are utilised in other metabolic pathways, e.g. DHAP (dihydroxyacetone phosphate) is reduced to give glycerol 3-phosphate, which is used in the formation of triglycerides.
- Glycolysis interconnects with other processes such as lactate and ethanol fermentation, transamination to form alanine, pentose phosphate pathway, glycogen metabolism, etc.
- When there is a high demand of energy in muscles and there is an insufficient supply of oxygen, anaerobic glycolysis pathway is used to generate energy.
- Erythrocytes derive energy from lactic acid fermentation as they are devoid of mitochondria. Lens of the eye is another example of anaerobic glycolysis.
- As most of the reactions are reversible, glucose is generated back from pyruvate by the process of gluconeogenesis.
Also Read: MCQs on Prokaryotes
Overview of Glycolysis
Glycolysis is a series of enzymatic reactions occurring in the cytoplasm. It is also known as the EMP pathway (Embden Meyerhof Parnas pathway). It is the first step in cellular respiration. Plants and animals derive energy from the breakdown of carbohydrates. Sucrose stored in the plants get converted to glucose and fructose. These monosaccharides enter the glycolytic pathway to generate energy.
- Two molecules of pyruvate are produced by partial oxidation of glucose.
- There are two phases; Preparatory phase, where ATP is consumed and Pay off phase where ATP is produced. There is a net yield of 2 ATPs and 2 NADH.
- It is a series of ten enzymatic reactions, where 6C Glucose is converted to 2 molecules of 3C pyruvate.
- In the first phase Glucose is phosphorylated to form fructose-1,6-bisphosphate in the three step process and then broken down to 3C compound G3P (Glyceraldehyde-3-phosphate) and DHAP (Dihydroxyacetone phosphate). The latter generates G3P. In this phase 2 ATPs are utilized.
- The second phase, which is an energy capturing phase. G3P is converted into pyruvate in five steps. Here we get 4 ATPs and 2 NADH are formed.
- In eukaryotic aerobic respiration, the pyruvate enters mitochondria, where it undergoes oxidative decarboxylation to form acetyl CoA, which enters Krebs cycle or Citric acid cycle. In aerobic prokaryotes, this reaction takes place in cytosol.
- In anaerobic respiration, pyruvate is converted into lactate, e.g. in muscles or acetaldehyde, which is converted into ethanol and CO2 in bacteria and yeast.