In this video, we will study about the process of glycolysis. The word glycolysis is made up of two words. The word glyco means glucose and the word lysis means breakdown. The glycolysis is a metabolic pathway that involves systematic breakdown of glucose to produce energy.
And the glycolysis takes place in the cytosol of the cells. First, we will have an overview about this process and then we will study about the various reactions involved. In glycolysis, one molecule of glucose which is a 6 carbon compound is broken down into two molecules of pyruvate which is a 3 carbon compound.
And in this conversion, energy is released in the form of ATP and NADH. The pyruvate formed is further utilized in various energy producing pathways that produces more energy. The process of glycolysis takes place in two phases. In the first phase, the glucose is first converted into two molecules of glyceraldehyde 3-phosphate.
Since this conversion involves addition of phosphate, the first phase actually uses energy instead of producing it. In the second phase, the glyceraldehyde 3-phosphate is converted into pyruvate and it is in the second phase energy is actually produced. Now let's look at the various reactions involved in the glycolysis.
So it all begins with a molecule of glucose that enters the cytosol and the first reaction that takes place is conversion of glucose to glucose 6-phosphate. The enzyme that catalyzes this reaction is called hexokinase. The word hexo means 6, denoting the 6-carbon compound glucose and the kinases are a group of enzymes that catalyze the phosphorylation reactions. So the enzyme hexokinase transfers a molecule of phosphate from ATP to glucose and converts glucose to glucose 6-phosphate.
In this reaction, ATP is converted into a molecule of ADP. Hence, it utilizes one molecule of ATP. Next, the glucose 6-phosphate is converted into its isomer, the fructose 6-phosphate by the enzyme isomerase.
This is a simple rearrangement reaction. In the next step, the fructose 6-phosphate is converted to fructose 1,6-bisphosphate. That is addition of another phosphate group at the first carbon of the fructose ring.
This reaction is catalyzed by the enzyme phosphofructokinase. Another kinase enzyme which transfers a group of phosphate from ATP to fructose 6-phosphate. And again ATP is converted into ADP. Hence another ATP is utilized in the reaction. Next, the Fructose-1,6-bisphosphate is split into two molecules, the glyceraldehyde 3-phosphate and dihydroxyacetone phosphate.
These both are three carbon compounds and the enzyme that catalyzes this reaction is called aldolase. These all reactions compose the first phase of glycolysis and as you can see energy is actually utilized in this process in the form of two ATPs. The two compounds glyceraldehyde 3-phosphate and dihydroxyacetone phosphate are actually isomers.
and can be interconverted into each other by the enzyme isomerase. But since the glyceraldehyde 3-phosphate is further utilized in the process of glycolysis, the equilibrium of this isomerization reaction is always towards the glyceraldehyde 3-phosphate. Also keep in mind that every molecule of glucose is split into two molecules, so every reaction of the second phase happens twice and produces twice a product. In the next reaction, the glyceraldehyde 3-phosphate is converted to 1,3-bisphosphoglycerate. This involves addition of a phosphate group at the first position of the phosphoglycerate.
The enzyme that catalyzes this reaction is the glyceraldehyde 3-phosphate dehydrogenase. And in this reaction, nicotinamide adenine dinucleotide, which is the coenzyme, is reduced to NADH, which is further utilized in the electron transport chain to produce more energy. Also, this reaction utilizes a molecule of inorganic phosphate. The 1,3-Bisphosphoglycerate is converted to 3-phosphoglycerate by the enzyme phosphoglycerate kinase.
This kinase enzyme transfers the phosphate group at the first position of phosphoglycerate to adenosine diphosphate and in this process, a molecule of ATP is generated. Next the 3-phosphoglycerate is converted to 2-phosphoglycerate. This is a simple rearrangement reaction that happens with the help of the enzyme phosphoglycerate mutase. Next, the 2-phosphoglycerate is converted to phosphoenolpyruvate.
The enzyme involved is enolase and magnesium ions are also utilized in this reaction. In the final step of glycolysis, the phosphoenolpyruvate is converted to pyruvate by the enzyme pyruvate kinase. The phosphate group at the phosphoenolpyruvate is transferred to ADP and converted to ATP.
This all composes the second phase of glycolysis. And as you can see energy is produced in the second phase of the glycolysis. Now let's first look at the net reaction of glycolysis and then we will understand it in brief.
We have one molecule of 6 carbon glucose that splits into two molecules of 3 carbon compound pyruvate. There is a net utilization of only 2 ADPs. Since 4 ADPs are used in the second phase but 2 ADPs are also produced in the first phase, there is a net use of only 2 ADPs.
2 molecules of inorganic phosphate are utilized in this step. 2 nicotinamide adenine dinucleotides are reduced to NADH molecules in conversion of glyceraldehyde 3-phosphate to 1,3-bisphosphoglycerate. So this was a brief overview of the process of glycolysis.
I hope you find this video helpful. Thank you so much for watching this video. Like our channel on YouTube for all the upcoming videos and make sure to like our channel on Facebook for flashcards and upcoming notifications.