Glycolysis, Parts 1 and 2


Hey guys, Kimberly and Kevin are here with you this week and the topic of discussion is Glycolysis. For those of you who may consider this topic as equally horrendous as calculus, it truly isn’t because I too, was under that impression and you will soon realize the simplicity once you complete our fun and interactive blog on Glycolysis. Enjoy!!

Before we can truly learn about Glycolysis, we must understand the basics:

  • Glycolysis can be described as the oldest of all metabolic pathways.
  • It takes place in ALL life.
  • It occurs in the cytoplasm of the cell.
  • It forms 2 pyruvate molecules from the breakdown of a glucose molecule.
  • It is NOT oxygen dependant, that is, it can occur in an anaerobic environment.
  • It produces a net gain of 2 NADH molecules AND 2 ATP molecules per glucose molecule.


Lysis means “to split.” Therefore, Glycolysis can be easily remembered as the splitting of glucose which is a 6 carbon structure into two pyruvates which are 3 carbon structures.


The Glycolysis process above can be divided in TWO phases:

1.) The Energy Investment Stage (Preparatory Stage) in which 2 ATP forms 2 ADP and occurs from step 1 to 5.

2.) The Energy Generation Stage (Payoff Stage) in which 4 ADP forms 4 ATP, 2 NAD+ forms 2 NADH and occurs from step 6 to 10.


If this is your reaction at the moment, then DO NOT PANIC! It gets easier after the following diagrams and explanations, so keep calm and LEARN GLYCOLYSIS! 😀

1.) Preparatory Stage – conversion of glucose to glyceraldehyde 3 – phosphate via phosphorylation.

  • Image

The numbers 1 to 5 represent the specific enzymes present as illustrated in the diagram above:

  • Enzyme 1 = Hexokinase; phosphorylates the glucose molecule to form glucose 6 – phosphate.
  • Enzyme 2 = Phosphohexose Isomerase; helps convert glucose 6 – phosphate to fructose 6 – phosphate.
  • Enzyme 3 = Phospho – fructokinase – 1; most important enzyme in terms of regulation.
  • Enzyme 4 = Aldolase; helps split the 6 carbon sugar phosphate to form the 3 carbon sugar phosphates.
  • Enzyme 5 = Triose Phosphate Isomerase; converts DHAP molecule into G3P molecule.

2.) Payoff Stage – conversion of G3P to pyruvate via oxidation and the formation of both ATP and NADH


The numbers 6 to 10 represent the specific enzymes present as illustrated in the diagram above:

  • Enzyme 6 = Glyceraldehyde 3 – phosphate dehydrgenase; catalyzes the oxidation of the aldehyde group to a carboxylic group and phosphorylates the G3P to 1,3 – BPG
  • Enzyme 7 = Phosphogylcerate kinase; 1,3 BPG loses a phosphate group which is transferred to an ADP molecule to form ATP
  • Enzyme 8 = Phosphoglycerate mutase; phosphate group on carbon 3 is removed and the one on carbon 2 remains.
  • Enzyme 9 = Enolase; dehydrogenation occurs.
  • Enzyme 10 = Pyruvate kinase; form ATP when converting PEP to pyruvic acid.


Have no fear my viewers because we’re almost at the end!! Let us move on to the Fates of Pyruvate. The following diagram is a simple illustration showing the different fates of pyruvate.


The following table represents the same concept as the previous diagram, however the structural formulas of the various conversion reactions of pyruvate are illustrated in this table.


1.) Aerobic Conditions – Entry into TCA cycle.

  • The pyruvate is converted to Acetyl – Co A via an oxidative decarboxylation reaction.
  • The enzyme that catalyses this reaction is pyruvate dehydrogenase.
  • This reaction can only occur if mitochondria are present.
  • This reaction is referred to as a link reaction because it links pyruvate to the TCA cycle.

2.) Anaerobic Conditions – Lactic acid Fermentation

  • The pyruvate is converted to lactate.
  • The enzyme that catalyses this reaction is lactate dehydrogenase.
  • Lactic acid fermentation regenerates NADwhich allows glycolysis to be completed as there are limited NAD+ molecules within a cell and is important for the erythrocyte.
  •  No ATP is generated when pyruvate is converted to lactate.

3.) Anaerobic Conditions – Alcoholic Fermentation

  • This is a 2 step reaction that first converts pyruvate to acetaldehyde and then to ethanol.
  •  The two enzymes that catalyse these reactions are pyruvate decarboxylase and alcohol dehydrgenase.
  • Pyruvate decarboxylase requires TPP as a cofactor for the enzyme to work.
  • Alcholic fermentation regenerates NADwhich allows glycolysis to be completed as there are limited NAD+ molecules within a cell.


AND THAT’S IT FOR MY PART GUYS!!!! Until next time.



Avril Chew. 2003. GCE ‘A’ Level Biology @ Your Fingertips. Singapore : Redspot Publishing. (accessed March 9th, 2014)

CJ Clegg with DG Mackean. 1994, 2003. Advanced Biology Principles and Applications. 2nd edition. London : Hudder Education. (accessed March,9th,2014)

BiochemJM You Tube Page. Glycolysis Parts 1 and 2. (accessed March 9th, 2014)