Difference Between Glycolysis and Fermentation

Edited by Diffzy | Updated on: April 30, 2023


Difference Between Glycolysis and Fermentation

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Glycolysis and fermentation are the two processes that people often get confused about. However, while reading about these topics, it’s important to understand about glycolysis and fermentation in detail. This gives us a deep insight into the topics and also makes people aware of the processes.

Various chemical reactions occur all around us. Regardless of our disinterest, we are once again confronted with two common processes: glycolysis and fermentation. The process begins in the cells of living creatures. They are undeniably different, but how different are they?

Today, let’s dive into these two common terms that we come across quite frequently in science and biology but still, we have to learn a lot many new and interesting things about them.

Glycolysis vs Fermentation

In reality, Glycolysis and fermentation actually differ majorly in a way that glycolysis may or may not require oxygen, whereas fermentation does not require oxygen. Glycolysis is the initial stage in the synthesis of the energy-storing molecule ATP, and it can go either one of the two ways once it's started: with or without oxygen. Fermentation is basically the result of an oxygen-free path.

Difference Between Glycolysis and Fermentation in Tabular Form

Parameters of Comparison Glycolysis Fermentation
Presence of Oxygen It is required. It is not required.
Occurrence It happens in mitochondria. It happens in the cytoplasm.
No. of ATP molecules released It releases 4 ATP molecules. It releases only 2 ATP molecules.
The chemical conversion It converts glucose to pyruvate. It converts Pyruvate to Lactic Acid and Alcohol.
The end products It releases 2 Pyruvate molecules,

2 NADH, and 4 ATP molecules.

It releases carbon dioxide, ethanol, and energy (Difference Between Glycolysis and Fermentation (With Table), n.d.).

What is Glycolysis?

The metabolic mechanism that transforms glucose (C6H12O6) into pyruvic acid is known as glycolysis (CH3COCO2H). The high-energy molecules adenosine triphosphate (ATP) and reduced nicotinamide adenine dinucleotide are formed from the free energy released during this process (NADH). Glycolysis is a set of ten enzyme-catalysed processes.

Glycolysis is a non-oxygen-dependent metabolic pathway. Glycolysis' widespread prevalence in various species suggests that it is an old metabolic mechanism.  Indeed, the events that make up glycolysis and its counterpart system, the pentose phosphate pathway, take place in the Archean oceans' oxygen-free environment, in the absence of enzymes and catalysed by metal.

There are two phases to the glycolysis pathway:

  • ATP is utilized during the investment phase.
  • The yield phase occurs when more ATP is created than is consumed.

It took almost a century to properly understand the glycolysis route as we know it today. To comprehend the process as a whole, the data of several smaller trials had to be pooled.

Basically, the wine business took the initial moves toward understanding glycolysis in the nineteenth century. The French wine business wanted to know that why wine occasionally tasted bad instead of turning into alcohol for economic reasons. Then  During the 1850s, French scientist Louis Pasteur conducted a study on this topic, and the findings of his tests began the long process of clarifying the glycolysis pathway. His research revealed that fermentation is carried out by live microorganisms, such as yeasts, and that yeast glucose intake is lower under aerobic settings than under anaerobic conditions (the Pasteur effect).

Basically, Eduard Buchner's non-cellular fermentation research in the 1890s provided insight into the component processes of glycolysis. Due to the action of enzymes in the extract, Buchner demonstrated that glucose could actually be converted to ethanol using a non-living yeast extract. So, this experiment not only changed biochemistry but also allowed scientists to study this pathway in a more controlled laboratory context. Arthur Harden and William Young uncovered more parts of glycolysis in a series of investigations from 1905 to 1911. They also figured out how ATP regulates glucose consumption during alcohol production. They also shed light on the significance of fructose 1,6-bisphosphate as a glycolysis intermediary.

So, when yeast juice was incubated with glucose, CO2 levels were measured and fructose 1,6-bisphosphate was discovered. CO2 generation accelerated at first, then slowed. If an inorganic phosphate (Pi) was added to the mixture, the process would restart, according to Harden and Young. Harden and Young determined that this procedure produced organic phosphate esters, and they were able to recover fructose diphosphate through later research (F-1,6-DP).


Because they consume energy to convert glucose into two three-carbon sugar phosphates, the first five stages of Glycolysis are referred to as the preparatory (or investment) phase (G3P).

The first stage involves the phosphorylation of glucose by a group of enzymes known as hexokinases, which results in glucose 6-phosphate (G6P). This reaction uses ATP, but it keeps the glucose concentration low, allowing glucose to enter the cell through the plasma membrane transporters continually. Furthermore, it prevents glucose from seeping out since the cell lacks G6P transporters, and the charged structure of G6P prevents free diffusion out of the cell. Alternatively, glucose can be produced through phosphorolysis or hydrolysis of intracellular starch or glycogen.

In animals, glucokinase, a hexokinase isozyme with a reduced affinity for glucose (Km in the area of normal glycemia) and different regulatory features, is also employed in the liver. The liver's function in managing blood sugar levels is reflected in this enzyme's varied substrate affinity and alternate regulation.

G6P is then reorganized by glucose phosphate isomerase into fructose 6-phosphate (F6P). Phosphorylation can also allow fructose to enter the glycolytic pathway at this point.

G6P is then reorganized by glucose phosphate isomerase into fructose 6-phosphate (F6P). Phosphorylation can also allow fructose to enter the glycolytic pathway at this point.

The structure change is an isomerization, in which G6P is changed to F6P. The phosphoglucose isomerase enzyme is required for the process to proceed. Under typical cell circumstances, this process is reversible. However, due to a low concentration of F6P, which is constantly consumed during the following step of glycolysis, it is frequently pushed forward. This process rapidly reverses in the presence of high F6P concentrations. The principle of Le Chatelier can explain this phenomenon. In the fourth reaction step, carbanion stabilization requires isomerization to a keto sugar.

Another ATP's energy expenditure in this stage is justified in two ways: The glycolytic process becomes irreversible (up to this point), and the energy supplied destabilizes the molecule. Because the reaction mediated by phosphofructokinase 1 (PFK-1) is connected to the hydrolysis of ATP (an energetically favorable step), it is essentially irreversible, and the reverse conversion during gluconeogenesis must take place via a separate pathway. As a result, the reaction becomes a crucial regulatory point.

Furthermore, the second phosphorylation event is required to allow the production of two charged groups (rather than just one) in the next step of glycolysis, preventing substrate-free diffusion out of the cell.

Aldolase splits the hexose ring into two triose sugars: dihydroxyacetone phosphate (a ketose) and glyceraldehyde 3-phosphate after destabilizing the molecule in the preceding process (an aldose). Aldolases are divided into two groups: class I aldolases found in animals and plants, and class II aldolases found in fungi and bacteria; the two groups cleave the ketose ring via different processes.

The alcohol group is formed when electrons delocalize during the cleavage of a carbon-carbon bond. The carbanion's structure, via resonance charge distribution, and the presence of a charged ion prosthetic group, stabilize the resulting carbanion.

Triosephosphate isomerase transforms dihydroxyacetone phosphate to glyceraldehyde 3-phosphate (GADP), which is then used in glycolysis. This is favorable because dihydroxyacetone phosphate is directed along the same pathway as glyceraldehyde 3-phosphate, making control easier.

The pay-off phase of glycolysis is defined by a net gain of the energy-rich molecules ATP and NADH in the second part of the process.  Each reaction in the pay-off phase occurs twice per glucose molecule because glucose produces two triose sugars in the preparatory phase. This produces 2 NADH molecules and 4 ATP molecules, giving the glycolytic process a net gain of 2 NADH molecules and 2 ATP molecules per glucose.

So basically, The triose sugars' aldehyde groups are oxidized, and inorganic phosphate is added, resulting in 1,3-bisphosphoglycerate.

Then, For each triose, the hydrogen is used to decrease two molecules of NAD+, which is a hydrogen transporter, to give NADH + H+.

Because the phosphate (Pi) group occurs in the form of a hydrogen phosphate anion (HPO42), which dissociates to supply the extra H+ ion and gives a net charge of -3 on both sides, both hydrogen atom and charge balance are preserved.

To create 1-arsenal-3-phosphoglycerate, arsenate (AsO43), an anion similar to inorganic phosphate, may be used instead of phosphate as a substrate. This, on the other hand, is unstable and quickly hydrolyzes to generate 3-phosphoglycerate, the next pathway's intermediate. The molecule of ATP created from 1-3 bisphosphoglycerate in the next reaction will not be made as a result of skipping this step, even though the process will proceed. As a result, arsenate acts as a glycolysis uncoupler.

This phase involves phosphoglycerate kinase transferring a phosphate group from 1,3-bisphosphoglycerate to ADP, resulting in ATP and 3-phosphoglycerate. Glycolysis has achieved the break-even threshold at this moment: two molecules of ATP have been used, and two new molecules have been generated. This step, one of two substrate-level phosphorylation steps, necessitates ADP, therefore it does not occur when the cell has plenty of ATP (but little ADP). This is an important regulatory point in the glycolytic pathway because ATP decays quickly when it is not processed.

Phosphoglycerate mutase is the enzyme that converts 3-phosphoglycerate to 2-phosphoglycerate.

2-phosphoglycerate is then converted to phosphoenolpyruvate by enolase. This is an elimination reaction that uses the E1cB mechanism.

Using the enzyme pyruvate kinase, a final substrate-level phosphorylation creates a molecule of pyruvate and a molecule of ATP. Similar to the phosphoglycerate kinase process, this serves as an extra regulatory step (Glycolysis, n.d.).

What is Fermentation?

Fermentation is actually a metabolic process that uses enzymes to induce chemical changes in organic substrates. It is also described as the extraction of energy from carbohydrates in the absence of oxygen in biochemistry. It can even refer to any procedure in which the action of microbes results in a beneficial alteration to a food or beverage in the food industry. Moreover,  Zymology is the scientific study of fermentation.

Fermentation is basically defined in the following sections. They range from more informal, generic meanings to more scientific ones.

  • Microorganisms actually used to preserve food (general use).
  • Any large-scale microbiological process that occurs in the presence or absence of air (the common definition used in industry, also known as industrial fermentation).
  • Any procedure that basically results in the production of alcoholic beverages or acidic dairy products is considered a manufacturing process (general use).
  • Any energy-releasing metabolic process that occurs solely in anaerobic environments (somewhat scientific).
  • Furthermore, Any metabolic activity that releases energy from a sugar or other organic molecule and employs an organic molecule as the final electron acceptor does not require oxygen or an electron transport mechanism (most scientific).

Biochemical Importance

Fermentation, like aerobic respiration, is a way of extracting energy from molecules. This is the only mechanism that all bacteria and eukaryotes use. As a result, it is thought to be the oldest metabolic route, suitable for prehistoric settings — before plant life, that is, before the presence of oxygen in the atmosphere. 

From the skins of fruits to the intestines of insects and mammals to the deep ocean, yeast, a type of fungus, may be found in practically any environment capable of maintaining bacteria. Sugar-rich compounds are converted (broken down) by yeasts into ethanol and carbon dioxide.

Basic fermentation pathways can be found in all cells of higher organisms. Fermentation occurs in mammalian muscle during periods of severe exercise when oxygen supply is limited, resulting in the production of lactic acid.  Fermentation also produces succinate and alanine in crustaceans. 

Fermentative bacteria are involved in the creation of methane in a variety of environments, including bovine rumens, sewage digesters, and freshwater sediments. Hydrogen, carbon dioxide, formate, acetate, and carboxylic acids are all produced. The carbon dioxide and acetate are then converted to methane by microbial colonies. Acetogenic bacteria oxidize acids to produce additional acetate, hydrogen, or format. Methanogens (in the Archea domain) then convert acetate to methane (Fermentation, n.d.).

Main Differences Between Glycolysis and Fermentation In Points

  • The initial stage of the process of cellular respiration is glycolysis. The breakdown of glucose, a six-carbon molecule that is divided into two molecules with three carbon atoms each, starts the process.
  • Fermentation, on the contrary, is an anaerobic chemical reaction that occurs during cellular respiration. Fermentation is also known as anaerobic respiration.
  • Glycolysis is a process that can take place in both the presence and absence of oxygen.
  • Because it happens when oxygen is limited, fermentation is the method of reaction that is likewise less efficient than the first.
  • Glycolysis is the breakdown of carbohydrates by enzymes.
  • Fermentation is in reality a metabolic process in which sugar is converted to acids, gases, or alcohol.
  • Ethanol or lactic acid are not produced during glycolysis.
  • Fermentation results in the production of ethanol or lactic acid (Thili, 2016).


Hence, we properly listed out the key differences between Glycolysis and Fermentation. It becomes very vital to understand in depth about these scientific processes that are essential for Nature.


  • Retrieved from WIKIPEDIA: https://en.wikipedia.org/wiki/Fermentation
  • Glycolysis. (n.d.). Retrieved from WIKIPEDIA: https://en.wikipedia.org/wiki/Glycolysis


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"Difference Between Glycolysis and Fermentation." Diffzy.com, 2024. Tue. 18 Jun. 2024. <https://www.diffzy.com/article/difference-between-glycolysis-and-fermentation-476>.

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