Glycolysis is a metabolic pathway and foundation for both aerobic and anaerobic cellular respiration It has evolved in all types of organisms. The scheme of glycolysis was given by Gustav Embden, Otto Meyerhof, and J.Parnas, and is often to referred as the (EMP) Embden-Meyerhof pathway. Glycolysis is the first step in the breakdown of glucose to extract energy for cellular metabolism. It consists of the energy required followed by an energy-releasing phase.
Metabolism is the greek word that means, “Change”. An organism change food into usable energy for cells. The human body takes all type of nutrient so based on the nutrients there are two types of pathway that occurs in the body to metabolize nutrients:
Catabolic Pathway: If a body breaks down a substance into macromolecules, we consider it Catabolic Pathway. This pathway release energy in the form of ATP.
Anabolic Pathway: If a body makes up a more complex molecule from the simpler precursor, we consider it Anabolic Pathway. In this process, energy requires to complete.
Although it is a part of the larger process of cellular respiration that involves glycolysis, Kreb’s Cycle, the electron transport chain, and ATP synthase, in this article, our scope is to focus on glycolysis.
What Is Glycolysis
Glycolysis is a series of reactions that extracts energy by splitting six-carbon glucose into three-carbon pyruvate. In this process 2 molecules of pyruvate along with ATP, NADH and water. Glycolysis occurs in the cytoplasm of a cell and does not require oxygen but occurs in both aerobic and anaerobic organisms i.e does not use oxygen.
Glucose is a six membraned ring structure found in the blood. It entered the cell through a specific type of protein that carries it from outside the cell into the cytoplasm of the cell. In the plant, this glucose is derived from sucrose which is the end product of photosynthesis. Sucrose is converted into glucose with the help of the enzyme invertase and these two monosaccharides readily enter the glycolytic pathway.
The overall reaction of glycolysis is represented as:
C6H12O6 + 2 NAD++2 ADP+ 2P=2Pyruvic acid (CH3(C=O)COOH+2ATP+2NADH+2H+
Detailed Phases Of Glycolysis:
Glycolysis occurs in two stages:
Stage-1: Energy Requiring Phases:
In the first stage of glycolysis, glucose is broken into two phosphorylated 3-carbon compounds through a series of reactions. In this stage, one molecule of glucose is converted into two molecules of Glyceraldehyde 3 phosphate. During the first stage of glycolysis, ATP does not use while 2 molecules of ATP consumes here for phosphorylation.
The first step in glycolysis is the conversion of glucose to glucose 6 phosphate by phosphorylation (The process of adding a phosphate group to a molecule derived from ATP) with the help of the enzyme hexokinase. For this reaction, it uses one molecule of ATP.
Step-2 Phosphoglucose Isomerase:
The second stage of glycolysis is isomerisation where glucose 6 phosphates are converted into fructose 6 phosphate by the activity of glucose [phosphate isomerase (Phosphoglucoisomerase). In this isomerisation process, 6 carbon membered ring is transformed into 5-membered rings. This reaction occurs because Fructose 6 Phosphate is readily cleavable.
Step 3 Phosphofructokinase:
In the third step of glycolysis Fructose, 6 phosphates are converted into fructose 1,5 bis phosphate by the phosphorylation process and ATP is used again in the process. Phosphofructokinase has been used as an enzyme and Mg+2 is used as a cofactor.
Step 4 Aldolase
Fructose 1,6 bisphosphate is cleaved into two sugar. These sugars are Dihydroxyacetone phosphate (DHAP) and glyceraldehyde 3 phosphate (GAP). They are isomers of each other and the enzyme aldolase participates in the breakdown of these sugars.
Step 5 Triose Phosphate Isomerase
The enzyme triose phosphate isomerase helps to convert the dihydroxyacetone phosphate into Glyceraldehyde 3 phosphate (GAP).
In the first stage of glycolysis, one molecule of glucose is converted into two molecules of Glyceraldehyde 3 phosphate. During the first stage of glycolysis, ATP does not use while 2 molecules of ATP consumes here for phosphorylation.
Stage-2 Energy Releasing Phase
During the second stage of glycolysis is two convert two molecules of Glyceraldehyde 3 Phosphate (GAP) are into pyruvate through a series of oxidative phosphorylation.
Step 6 Glyceraldehyde 3Phosphate Dehydrogenase:
This step undergoes two reactions: 1) Glyceraldehyde 3 Phosphate will be oxidized by the enzyme nicotinamide adenine dinucleotide. Glyceraldehyde 3 phosphate dehydrogenase allows the NAD to take hydrogen of the Glyceraldehyde [phosphate converting the NAD to NADH. 2) Glyceraldehyde 3 phosphate dehydrogenase adds a phosphate to form 1,3 bisphosphoglycerate, NADH and a hydrogen atom. NADH is a high-energy electron carrier, it can be used to generate ATP in cellular respiration.
Step 7 Phosphoglycerate Kinase:
In the 7-step 1,3 bisphosphoglycerate is converted to 3 phosphoglycerates by the removal of the phosphate group from 1,3 bisphosphoglycerate and the activity of the enzyme Phosphoglycerate Kinase (PGK) takes part in this reaction. Energy generates in this step in the form of ATP.
Step 8 Phosphoglycerate Mutase:
With the help of the enzyme Phosphoglycerate mutase P transfers from 3-Phosphoglycerate from the third carbon to the 2nd carbon to form 2 phosphoglycerate. Mutase catalyzes the transfer of functional groups from one position on a molecule to another.
Step 9 Enolase
In step 9 enolase enzyme helps to remove water molecules from 2-Phosphoglycerate and form phosphoenol pyruvate (PEP). PEP is a high-energy compound.
Step 10 Pyruvate Kinase:
In the last step of glycolysis PEP is converted into pyruvate and forms ATP by transferring a phosphate group to ADP. Pyruvate Kinase takes part in this reaction. There are two molecules of PEP, hence it generates two ATP molecules.
Stage 1 produces two molecules of Glyceraldehyde 3 phosphate (GAP), which means we need to go through again in stage 2 for the second molecule of GAP.
In the end, two molecules of NADH, 2 molecules of ATP and two molecules of pyruvate will use later in the metabolic process.
Summary Of Glycolysis:
- Stage 1 produces two molecules of Glyceraldehyde 3 phosphate (GAP), which means we need to go through again in stage 2 for the second molecule of GAP.
- In the end, two molecules of NADH, 2 molecules of ATP and two molecules of pyruvate will use later in the metabolic process.
Step 1 & 3 consumes two ATP=-2 ATP
Step 7 and 10 uses two ATP= +4 ATP