Glycolysis - A partial oxidation of glucose into Pyruvic acid

Overview 

• The term glycolysis has been  derived from the Greek words glycos means sugar, and lysis  means splitting. 

• The scheme of glycolysis  has been given by the  Gustav Embden, Otto Meyerhof, and J. Parnas,  therefore this process is also known as  EMP pathway. 

• Glycolysis occurs in the cytoplasm of the cell and is present in all living organisms. In this process, glucose  is partial oxidized and  form two molecules of pyuruvic acid.

• In plants, this glucose is derived from sucrose. This sucrose is synthesized in plants during the photosynthesis. which is the end product of photosynthesis, or from storage carbohydrates. 

• Sucrose is converted into glucose and fructose by the enzyme invertase. The step of glycolysis for the glucose and fructose are same. These two mono saccharides enter in to the glycolytic pathway.

• In glycolysis, a chain of  reactions, under the control of different enzymes, takes place to produce pyruvic  acid from glucose. During the process of glycolysis, the utilisation or synthesis of ATP or NADH + H+ take place. 

• The complete process of glycoysis can be understood in to the following step.

STEP -1 

• Glucose and fructose undergo phosphorylation and give rise to glucose-6- phosphate by the activity of the enzyme  hexokinase. 

STEP-2 

• This glucose-6- phosphate  is converted into fructose-6- phosphate by the process of isomerisation. This step is catalyzed by the enzyme phosphofructo kinase.

• ATP is utilised in two steps during the glycolysis. First the phosphorylation  of glucose into glucose 6-phosphate and second  during the isomerisation of fructose 6-phosphate to fructose 1, 6-bisphosphate. 

STEP -3

• The fructose 1, 6-bisphosphate is differentiated into  into dihydroxyacetone  and 3-phosphoglyceraldehyde in presence of enzyme aldolase.

• To proceeds the completion of glycoysis, Out of dihydroxyacetone and 3-phosphoglyceraldehyde,

• The 3-phosphoglyceraldehyde is converted into 1,3-bisphosphoglyceric acid.This step of glycolysis is catalysed by enzyme glyceraldehyde dehydrogenase.

• During the conversion of 3 phosphoglyceraldehyde into 1,3,bisphosphoglyceric acid, NADH2 is formed from NAD+.

STEP -4 

• The conversion of Biphosphoglyceric acids into 3-phosphoglyceric acid is catalysed by enzyme phosphoglycerokinase.

• This step is  an energy yielding process and  this energy is stored by the formation of ATP. 

STEP -5   

• 3- phosphoglyceric acid is converted into 2 phosphoglyceric acids in presence of enzyme phosphoglyceromutase.

STEP -6 

• 2- phosphoglyceric acid is now transformed into 2 phosphoenolpyruvic acid.

• This reaction takes place in the presence of enzyme enolase. During this step 2 molecules of water are also released.

STEP -7

• 2 phosphoenol pyruvic acid is finally converted into two molecules of pyruvic acid.

• One molecule of ATP is synthesised during the conversion of phosphoenolpyruvic acid into pyruvic acid. This reaction occur in presence of enzyme pyruvate Kinase.

• During the complete process of glycolysis, two molecules of ATP are used and two molecules of ATP are used.

• Besides these, one molecule of NADH2 is also formed. Pyruvic acid is the key product of glycolysis.

• There are three methods and these methods belong to three different cells where pyruvic acid produced by glycolysis is used .

• These are lactic acid fermentation, alcoholic fermentation and aerobic respiration.