What is glycolysis? steps of glycolysis:

In this post you will know what is glycolysis?And the different steps of glycolysis? where does glycolysis takes place ? Preparatory and payoff phase of glycolysis.

What is glycolysis:

➡️The term glycolysis is derived from the Greek word glykys and sugar (Glykys means sweet and lysis means splitting). The complete pathways of glycolysis was discovered by the three scientists namely Embden,Meyerhoff, And Parnas in the year of 1940.

➡️Glycolysis is the process by which a molecule of glucose is degraded to form two molecule of three carbon containing compound, pyruvate .

This happens by a series of enzyme catalyzed reactions.

➡️Glycolysis is regarded as an almost universal central pathway of Glucose catabolism.

In some mammalian tissue cell types ( such as Red blood cell, brain ,sperm etc) glycolysis is the sole source of metabolic energy due to the breakdown of the 6 carbon containing molecule glucose, which provides energy.

➡️There is also present , many anaerobic microorganisms which are also completely dependent on the process of glycolysis,to acquire energy.

➡️Some aquatic plants are dependent on the process of glycolysis , for energy.

➡️ The enzymes which takes part upin the process of glycolysis are present in the cytosomal fraction of the cell.

➡️If the process of glycolysis happens in the absence of oxygen then it is known as anaerobic condition,and in this condition lactate is the final product.

➡️And If the process of glycolysis happens in the presence of oxygen then it is known as aerobic condition, and in this condition pyruvate is the final product, which then further oxidized to produce carbon dioxide and water.

Glycolysis metabolic pathway 2.svg , Image by-Thomas Shafee , Source , License-CC BY4.0

Steps of glycolysis:

1.Preparatory phase,in this process ATP(adenosine tri phosphate) is consumed.
➡️ The entire pathway of glycolysis is divided into two distinct phases which are known as

2.The Payoff phase,in this phase of glycolysis ATP is formed.

✡️ Preparatory phase of glycolysis:

In this phase of glycolysis two molecules of ATP are utilized and the hexose chain is cleaved into two molecules of triose phosphates.

Steps:

1.Phosphorylation of Glucose molecules:

Firstly Glucose is phosphorylated by ATP to produce ADP and Glucose-6-phosphate.

The enzyme namely hexokinase or glucokinase helps in this reaction.

The enzyme hexokinase is dependent on Mg2+ for its activity.

The enzyme hexokinase which splits the ATP into ADP and Pi is added onto the glucose molecule.

This enzyme is present in most of the body tissues.

On the other hand the enzyme glucokinase is present in the liver ,and catalyses the phosphorylation of only glucose molecule.

2.Conversion of Glucose 6 phosphate to Fructose 6 phosphate:

In this phase Glucose 6 phosphate , which produced in the first step, undergoes isomerization and gives Fructose 6 phosphate .

The enzyme which helps in this isomerization process is phospho hexose isomerase (Phospho glucose isomerase). And Mg2+ also helps in this process.

3.Phosphorylation of Fructose 6 phosphate ant formation of Fructose 1,6 bisphosphate:

In this step phosphofructokinase-1 catalyzes the transfer of a phosphoryl group from Adenosine-tri-phosphate to the ketose molecule fructose 6 phosphate and helps in the production of fructose1,6-bisphosphate .

This reaction is irreversible in nature and it is also known as the regulatory step of glycolysis.

4.Breakdown of Fructose 1,6-bisphosphate:

In this step 6 carbon molecules fructose 1,6-bisphosphate splits into two three carbon molecules namely glyceraldehyde -3- phosphate and the other one is dihydroxyacetone phosphate.

The enzyme fructose 1,6 bisphosphate aldolase often simply known as aldolase catalyses reversible aldol condensation reaction.

5. Interconversion of triose phosphate:

From this phase 3 carbon containing molecule ,glyceraldehyde -3phosphate ,leads the further glycolysis process.

However, another there carbon containing molecule which formed in the previous step, dihydoxy acetone phosphate can rapidly be converted to geyceraldehyde 3 phosphate.

The enzyme namely triose phosphate isomerase helps in this reversible interconversion process.

Thus, from glycolysis two molecules of 3 carbon containing molecule glyceraldehyde 3 phosphate is obtained from one molecule of hexose (glucose)

Steps of glycolysis

✡️The payoff phase:

The payoff phase of glycolysis includes energy conserving phosphorylation steps.In this step some of the chemical energy of the glucose molecule is conserved in the form of ATP and NADH.

1.Glyceraldehyde 3 phosphate oxidezed to 1,3 bisphospho glycerate :

This step is involved in the formation 1,3 bisphospho glycerate from glyceraldehyde -3 phosphate.

The enzyme glyceraldehyde 3 phosphate dehydrogenase is involved in this reaction.This step also requires an inorganic phosphate molecule.

This step is also involves in the formation of NADH+ and H+ from NAD.

2.Phosphoryl transfer ,from 1,3 -Bisphospho glycerate to ADP:

In this step high energy phosphoryl group from the carboxyl group of 1,3 -bisphospho glycerate transfers to ADP with the help of the enzyme phospho glyceratekinase and forms 3-phospho glycerate and ATP.

This step is regarded as a good example of substrate level phosphorylation.

This reaction is reversible in nature

3.Formation of 2 phospho -glycerate from 3 phospho -glycerate:

With the help of the enzyme phospho glycerate mutase 3phospho glycerate converted to 2 phospho glycerate.

Between C2 and C3 of glycerate, phosphoglycerate mutase catalyzes a reversible shift of the phosphoryl group to help in the formation 2phosphoglycerate . An inorganic molecule namely Mg2+ is essential for this reaction.

4.Dehydration of 2-phosphoglycerate to phospho enol pyruvate:

The high energy compound phospho enol pyruvate forms in this reaction with the help of the enzyme enolase, which dehydrates 2- phosphoglycerate .

Basically in 2 -phosphoglycerate low energy phosphate ester bond is present which convets into high energy phosphate bond in to the molecule phosphoenolpyruvate after the dehydration process.