Physiological Metabolism Glycolysis: Steps & Importance

Key Concepts:

• Introduction
• Energy flow in ecosystem= Glycolysis
• Glycolysis process
• Glycolytic pathway
• Glycolysis regulation
• Importance of glycolysis

Introduction

Energy flow in ecosystem 

The food chain and food web facilitate the movement of energy. Plants collect sunlight with the aid of chloroplasts during the process of energy flow in the ecosystem, and a portion of it is turned into chemical energy during photosynthesis. When herbivores (primary consumers) eat the plants as food, this energy is stored in various organic products in the plants and passed on to the primary consumers in the food chain. The chemical energy contained in plant products is then converted into kinetic energy, and energy is degraded by heat conversion.  

The flow of energy in the ecosystem is one of the most important variables in the survival of such a large number of creatures. Solar energy is the principal source of energy for practically all species on Earth. It’s amusing to learn that we only receive around half of the sun’s effective radiation on Earth. When we say effective radiation, we mean radiation that plants can employ to perform photosynthesis. 

Glycolysis  

The process of converting glucose into energy is known as glycolysis. It generates two pyruvate molecules, together with ATP, NADH, and water. It can be found in both aerobic and anaerobic species. Glycolysis is a series of ten enzyme-catalyzed processes that convert glucose to pyruvate while also producing ATP. It is a universal pathway found in all living cells. Glycolysis occurs in all of the body’s cells. In this pathway, enzymes are found in the cytosomal part of the cell.  

Glycolysis is the first stage in the process of cellular respiration, which occurs in all organisms. The Krebs cycle follows glycolysis during aerobic respiration. In the absence of oxygen, cells produce small quantities of ATP by glycolysis, which is followed by fermentation. Three German scientists, Embden, Meyerhof, and Parnas, identified this mechanism, also known as the EMP Pathway. 

Glycolysis Process  

Glycolysis is an anaerobic oxidative process since it takes place in the absence of free oxygen and results in hydrogen loss. One molecule of glucose is broken down into two molecules of pyruvic acid throughout this process. Two molecules of ATP are utilized to create four molecules of ATP. 

This procedure is divided into two stages: 

1. Preparatory or Energy Investment  
2. Pay-off or Energy Harvesting Phase  

The initial stage of the glycolysis process (Energy investment phase) entails enclosing the glucose molecule within the cell. Here, energy is employed to change it such that the 6-carbon sugar molecule divides equally into two 3-carbon molecules. Energy is taken from molecules and stored in the form of NADH and ATP during the second stage of glycolysis (energy production phase). 

1. Preparatory or Energy Investment Phase– The preparatory or energy investment phase occurs when glucose is converted to glyceraldehyde-3-phosphate and energy, or ATP is used. 

2. Pay-off or Energy Harvesting Phase– Triose phosphates are converted to pyruvate during this phase, and energy or ATP is generated. 

Glycolytic Pathway  

Glycolysis is a group of mechanisms that break down one glucose molecule into two pyruvate molecules. Plants acquire glucose from sucrose or stored carbohydrates. Sucrose is broken down in plants by the enzyme invertase into glucose and fructose, and these two monosaccharides easily enter the glycolytic pathway. This glycolytic process is divided into ten phases. Each stage is catalyzed by a different enzyme. 

Step 1 – Phosphorylation of Glucose: In this stage, glucose is phosphorylated by ATP in the presence of Mg²⁺ and the enzyme hexokinase to create Glucose-6-phosphate. 

Step 2 – Synthesis of Fructose-6-Phosphate: This is a reversible process in which the enzyme phosphohexose isomerase isomerizes phosphorylated glucose (Glucose-6-phosphate) to produce Fructose-6-phosphate. 

Step 3 – Fructose-1,6-bisphosphate formation: Fructose-6-phosphate is phosphorylated into fructose-1,6-bisphosphate, and ADP with the help of the enzyme phosphofructokinase and ATP. 

Step 4 – Splitting: The enzyme aldolase splits fructose-1,6-bisphosphate into two 3-carbon molecules, Dihydroxyacetone Phosphate (DHAP) and 3-Phosphoglyceraldehyde (3-PGAld). 

Step 5 – Isomerization: The enzyme triosephosphate isomerase may transform the 3-carbon triosephosphate molecule Dihydroxyacetone Phosphate to 3-Phosphoglyceraldehyde and vice versa (reversible reaction). 

Step 6 – Oxidation and Phosphorylation – 3-Phosphoglyceraldehyde is transformed to 1,3-Bisphosphoglyceric acid and NADH+H+ is produced during this process. This process is aided by the enzyme phosphoglyceraldehyde dehydrogenase (reversible reaction). 

Step 7 – Phosphorylation of the Substrate Level: 1,3-Bisphosphoglyceric Acid through Enzyme Action 3-Phosphoglyceric acid and ATP were produced by phosphoglycerokinase. This is known as substrate-level phosphorylation because it involves the direct production of ATP from metabolites (reversible reaction). 

Step 8 – Isomerization II: Phosphoglyceromutase enzymes isomerize 3-phosphoglyceric acid to create 2-phosphoglyceric acid (reversible reaction). 

Step 9 – Dehydration: It occurs when 2-Phosphoglyceric acid releases one molecule of water in the presence of the enzyme enolase and Mg²⁺ to create 2-Phosphoenol pyruvic acid (reversible action). 

Step 10 – Pyruvate formation: In the last stage, 2-Phosphoenol pyruvic acid is changed to Pyruvic acid by removing phosphorus, resulting in the formation of one molecule of ATP from ADP via substrate-level phosphorylation with the activity of the enzyme pyruvic Kinase. The final result of glycolysis is pyruvic acid. 

Glycolysis Regulation  

Glycolysis is governed by three regulatory enzymes: hexokinase or glucokinase, phosphofructokinase, and pyruvate kinase, as well as glucose concentration in the blood and a particular hormone level in the blood. 

1. Glucose-6-phosphate inhibits hexokinase activity. Due to product inhibition, this enzyme inhibits the buildup of glucose-6-phosphate. 

2. Phosphofructokinase (PFK) is the most significant glycolysis regulating enzyme. It is an allosteric enzyme that is controlled by allosteric effectors such as ATP. 

3. Pyruvate kinase (PK) is inhibited by ATP and activated by fructose-1,6-bisphosphate. When dephosphorylated, pyruvate kinase becomes active; when phosphorylated, it becomes inactive. cAMP-dependent protein kinase inactivates pyruvate kinase. This pathway is used by the hormone glucagon to stimulate hepatic glycolysis. 

Importance Of Glycolysis  

• As glycolysis occurs in the cytoplasm, it is a critical step for energy production in species that lack mitochondria. 
• Pyruvate, the end result of glycolysis, is an intermediary in a variety of different processes such as gluconeogenesis, fatty acid production, fermentation, and so on. 
• Even glycolysis intermediates are employed in other metabolic pathways; for example, DHAP (dihydroxyacetone phosphate) is reduced to yield glycerol 3-phosphate, which is used in the synthesis of triglycerides. 
• Glycolysis is linked to other processes such as lactate and ethanol fermentation, alanine transamination, the pentose phosphate pathway, glycogen metabolism, and so on. 
• When there is a high demand for energy in the muscles but not enough oxygen, the anaerobic glycolysis pathway is employed to create energy.