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Biochemistry

Glycolysis Pathway: Definition, Steps.

Glycolysis is a Greek Word where Glykys means Sweet and Lysis means Splitting.

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SouravBio
This article writter by SouravBio on January 17, 2021

Writer and Founder of Microbiologynote.com. I am from India and my main purpose is to provide you a strong understanding of Microbiology.

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Glycolysis Pathway: Definition, Steps
Glycolysis Pathway: Definition, Steps
  • Glucose is the primary component in the metabolism of plants, animals, and many microorganisms due to the rich potential energy and good fuel.
  • Glucose stores as a starch or glycogen, when energy demands these are released as glucose to produce ATP either aerobically or anaerobically.
  • In animal and plants, there are four major pathway of glucose utilization such as; the synthesis of complex polysaccharides destined for the extracellular space; stored in cells (as a polysaccharide or as sucrose); oxidized to a three-carbon compound (pyruvate) via glycolysis to provide ATP and metabolic intermediates, or oxidized via the pentose phosphate (phosphogluconate) pathway to yield ribose 5-phosphate for nucleic acid synthesis and NADPH for reductive biosynthetic processes.
  • The photosynthetic organisms get their glucose by reducing atmospheric CO2 to triose and then triose to glucose.
  • The non-photosynthetic organisms get their glucose from simpler three or four carbon precursors via gluconeogenesis. It is reverse glycolysis with the helps of different glycolytic enzymes.

Glycolysis Pathway Definition

  • Glycolysis is a type of metabolic pathway where one molecule of glucose degraded into 2 molecules of 3 carbon-containing pyruvate molecules through a  series of enzyme-catalyzed reactions.
  • Glycolysis pathway also known as Embden-Meyerhof-Parnas Pathway.
  • Glycolysis is a Greek Word where Glykys means Sweet and Lysis means Splitting.
  • The glycolysis is a 10 step process, where the first 5 steps is known as Preparatory phase and the last 5 steps known as payoff phase.
  • In Preparatory phase Glucose is converted into Glyceraldehyde 3 phosphate and Dihydroxyacetone phosphate. In the payoff phase, the Glyceraldehyde 3 phosphate is converted into 3 carbon-containing pyruvate.
  • In Preparatory phase 2 molecules of ATP are used up while in payoff phase 4 molecules of ATP are generated.

Glycolysis Steps

Glycolysis Pathway: Definition, Steps
Glycolysis Pathway: Definition, Steps | Image Source: https://miro.medium.com/max/700/0*R6_3FLZHGlAaLXJA.png

Preparatory Phase

  1. Phosphorylation of Glucose: In this step, D-Glucose is phosphorylated with the help of the enzyme hexokinase. The hexokinase enzyme is a class of transferase enzyme. This enzyme transfers the phosphoryl group from ATP to the OH group of C6 carbon in Glucose and form Glucose 6 phosphate. In this step, Mg2+ is required.
  2. Conversation of Glucose 6 Phosphate to Fructose 6 Phosphate: In this step, the enzyme Phosphohexoisomerase catalyze the conversation reaction of Glucose 6 Phosphate to Fructose 6 Phosphate. This enzyme triggers the isomerization of Glucose 6 phosphate. In this step, Mg2+ is required.
  3. Phosphorylation of Fructose 6 Phosphate: In this step, enzyme phosphofructokinase-1 (PFK-1) catalyzes the phosphorylation reaction of Fructose 6 Phosphate and forms Fructose 1,6 Bisphosphate.
  4. Cleavage of Fructose 1,6 Bisphosphate: Enzyme aldolase or fructose 1,6-bisphosphate aldolase cleave the Fructose 1,6 Bisphosphate into two triose phosphates such as Glyceraldehyde 3 phosphate (aldose) and Dihydroxyacetone phosphate (Ketose). In this step, Mg2+ is required.
  5. Interconversion of triose phosphates: The enzyme triose phosphate isomerase converts the Dihydroxyacetone phosphate into Glyceraldehyde 3 phosphate.

Payoff Phase

  1. Oxidation of Glyceraldehyde 3 phosphate: The enzyme Glyceraldehyde 3 phosphate dehydrogenase converts the Glyceraldehyde 3 phosphate into 1,3-Bisphosphoglycerate with the help of 2 molecule of Pi and 2 molecules of NAD+.
  2. Conversation of 1,3-Bisphosphoglycerate to 3 phosphoglycerate: The enzyme phosphoglycerate kinase transfer one molecule of a phosphoryl group from 1,3-Bisphosphoglycerate to ADP and forms 3 phosphoglycerate and ATP. In this step, Mg2+ is required.
  3. Conversation of 3 phosphoglycerate to 2 phosphoglycerate: The enzyme phosphoglycerate mutase catalyzes the reversible shift of phosphoryl group between C-2 and C-3 of glycerate and forms 2 phosphoglycerate from  3 phosphoglycerate. In this step, Mg2+ is required.
  4. Dehydration of 2-Phosphoglycerate to Phosphoenolpyruvate: The enzyme enolase removes one molecule of H2O from 2-Phosphoglycerate and forms Phosphoenolpyruvate.
  5. Transfer of the Phosphoryl Group from Phosphoenolpyruvate to ADP: The enzyme pyruvate kinase transfers the phosphoryl group from Phosphoenolpyruvate to ADP to yield pyruvate and ATP. In this step K+ and either Mg2+ or Mn2+ si required.
Glycolysis Pathway: Definition, Steps
Glycolysis Pathway Steps

The overall equation of glycolysis is;

Glucose + 2NADP+ + 2Pi = 2 Pyruvate + 2ATP + 2NADPH + 2H+ + 2H2O

Important Notes

  • When more than one enzyme catalyzes the same reaction but is encoded by different genes is known as isozymes.
  • In glycolysis, 2 molecules of ATP and 2 Molecules of NADPH is generated.

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Writer and Founder of Microbiologynote.com. I am from India and my main purpose is to provide you a strong understanding of Microbiology.

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