Glycolysis takes place in eukaryotic cells
Glycolysis takes place in eukaryotic cells

Where does glycolysis take place in eukaryotic cells?

Glycolysis takes place in eukaryotic cells

Explain glycolysis – Glycolysis is the first stage of cellular respiration that involves the breaking down of glucose into smaller molecules to create an ATP molecule (cellular energy).

Glycolysis enzymes

In most organisms, Glycolysis takes place in the cytosol because that’s where sugar and other related enzymes can be seen in large concentrations. As soon as we consider viruses, which are not considered living organisms, glycolysis doesn’t occur at all.

  • Glycolysis occurs in the cytosol of living organisms
  • Viruses aren’t Considered living organisms and don’t execute glycolysis

The glycolysis process is how cells break down glucose to obtain the energy stored in the bonds between the electrons. In other words, it is also called as glucose metabolism. You can also say that the glycolysis process requires glucose. The other measures occur in the mitochondria. It’s a continuous process since the cells have a constant need for energy.

Table 1. Human enzyme deficiencies and genetic disease

Glycolytic enzyme Mutation-associated demonstrated or possible defects
Hexokinase I Nonspherocytic hemolytic anemia
Hexokinase II Nonspherocytic hemolytic anemia; insulin resistance; possible cause of increased glycolysis in cancer cells
Glucokinase Gestational diabetes; hyperinsulinism of the newborn; maturity-onset diabetes of the young
Phosphoglucose isomerase Nonspherocytic hemolytic anemia
Phosphofructokinase Exercise intolerance and compensated hemolysis (Tarui disease)
Aldolase B Hereditary fructose intolerance
Triosephosphate isomerase Multisystem disease, lethality in early childhood
Glyceraldehyde-3-phosphate dehydrogenase Diverse nonglycolytic functions, could be involved in, e.g., prostate cancer, age-related neurodegenerative disease
Phosphoglycerokinase Chronic hemolytic anemia
Phosphoglycerate mutase Exercise intolerance
Enolase I Deregulation of c-myc oncogene
Pyruvate kinase α-Hereditary hemolytic anemia

What is glycolysis define cellular respiration also explain glycolysis in detail

Glycolysis definition

Define glycolysis – Energy from glucose by dividing it into two three-carbon molecules known as pyruvates. Glycolysis is an ancient metabolic pathway, which means that it evolved long ago, and glycolysis location is in the great majority of organisms residing today^2,3start superscript, 2, comma, 3, ending superscript.

Does glycolysis require oxygen?

In Organisms that perform cellular respiration, glycolysis is the very first phase of the process.  But, glycolysis does not require oxygen and many anaerobic organisms–organisms that don’t use oxygen also have this particular pathway.


Important Terms in Glycolysis

Term Meaning
Cellular respiration The process by which organisms break down glucose into a form that the cell can use as energy
ATP Adenosine triphosphate, the primary energy carrier in living things
Mitochondria The eukaryotic cell structure where cellular respiration occurs
Cytoplasm The contents of a cell between the plasma membrane and the nuclear envelope; includes cytosol which is the jelly-like substance that fills the space between organelles
Aerobic A process that requires oxygen
Anaerobic A process that does not require oxygen
Fermentation An anaerobic pathway for breaking down glucose



Why the 1st phase are same in aerobic and anaerobic respiration cells

Glycolysis and gluconeogenesis

Glucose oxidation

This is only because oxidation in glycolysis does not involve Oxygen molecules. It’s the only movement of hydrogen. So it is behaving in precisely the same manner with or without oxygen.

Glycolysis vs gluconeogenesis

The main difference between glycolysis and gluconeogenesis is in their basic function: one depletes existing glucose, while other replenish it from both organic (carbon-containing) and inorganic (carbon-free) molecules. This makes metabolism|metastasis} a catabolic process of metabolism, whereas gluconeogenesis is anabolic.

Also on the glycolysis vs. gluconeogenesis front, whereas metabolism happens within the protoplasm of all cells, gluconeogenesis is confined chiefly to the liver.

Irreversible steps of glycolysis

Conversion of glucose into glucose 6 phosphate, fructose 6 phosphate into fructose 1,6 bisphosphate, phosphoenolpyruvate into pyruvic acid are irreversible i.e. step 1,3,10.


In addition to ATP, what are the end products of glycolysis?

Krebs cycle: within the mitochondrial matrix, the acyl CoA combines with the four-carbon compound salt to yield the six-carbon molecule turn. This molecule is pared back down to oxaloacetate, with the loss of two CO2 and the gain of one ATP, three NADH and one FADH2 (another electron carrier) per turn of the cycle.

This means you would like to double these numbers to account for the actual fact that 2 acyl CoA enters the Krebs citric acid cycle per molecule of aldohexose getting into metastasis.

Electron transport chain:

In these reactions, that occur on the mitochondrial membrane, the hydrogen atoms (electrons) from the aforementioned electron carriers are stripped off their carrier molecules used to drive the synthesis of an excellent deal of ATP, concerning thirty-two to thirty-four per “upstream” aldohexose molecule.


Glycolysis regulation

Glycolysis is regulated by the concentration of glucose in the blood, the relative concentration of critical enzymes, the competition for the intermediate products of glycolysis and the levels of certain hormones in the bloodstream. Humans and other mammals produce the hormone insulin in response to the ingestion of carbohydrates.

How do cells release energy from glucose?

High sugar levels stimulate the pancreas to produce insulin, which enhances the entry of glucose into the cell and increases the production of the critical glycolysis enzymes.


The catalyst hexokinase kickstarts the primary steps of the metabolic process, the conversion of glucose to glucose-6-phosphate, or G6P. Hexokinase competes with another catalyst, glucokinase, that turns glucose into glucose-1-phosphate, or G1P.


Phosphofructokinase (PFK) is that the catalyst that controls the third step of the metabolic process, the conversion of fructose-6-phosphate (F6P) into fructose-1,6-biphosphate (F1,6BP). It works by transferring a phosphate group from ATP to F6P. This is that the slowest reaction in the metabolic process and thus is the rate-limiting step.

Pyruvate Kinase

The tenth and final step of the metabolic process is the conversion of phosphoenolpyruvate (PEP) into pyruvate within the presence of the catalyst pyruvate enzyme (PK). This step increases the concentration of ATP in the cell, and high ATP levels inhibit PK.

When NAD has been turned into NADH, G3P(5H) loses two electrons and”two” protons.  But at the next step, 3-bis…, there’s nevertheless 4H. How?


Another H comes from HPO4 using a 2- fee which eventually turns itself to inorganic phosphate. In the Investment phase, where did the 2 atps come from this were consumed? Was it taken from somewhere else? If the purpose is to generate ATP in glycolysis, where do we get ATP to start the procedure?

The ATPs originally came out of your mother through parental nourishment, while you were developing in the womb. When you’re born you are going to have a stockpile of ATP in the body, which must be replenished to remain alive.

The body has many ways to make ATP, which may be seen by taking a look at the vast amount of metabolic responses that occur together with the body. That is why we could endure for a long time with no extra consumption of meals as the numerous catabolism pathways in the body which breakdown larger molecules and transfer the energy from the breakdown into ATP.

When food is abundant the breakdown of glucose by glycolysis and the Krebs cycle will create much more ATP compared to two ATPS required in the investment phase.

Additionally, this investment phase aids in controlling the metabolic reactions which take place in our body/cells.


Why fructose-1,6-bisphosphate is unstable?

One important note is the enzyme which catalyzes the once fructose-1,6-bisphosphate is formed it will be broken down to both carbon atoms at precisely the same speed.

How does glucose enter the cell

The way it’s sped up or slowed down is because of phosphofructokinase the enzyme which catalyzes the reaction to make fructose-1,6-bisphosphate is regulated by both ATP and ADP, when ATP levels are high it is inhibited and less fructose-1,6-bisphosphate will be generated when ADP levels are high it’ll be activated and much more fructose-1,6-bisphosphate will be created.

This permits the cells a way to regulate the breakdown of glucose-based upon the energy needs of the cell. Glycolysis Is a breakdown of sugar in anaerobic conditions to attain energy stored in sugar molecules. It takes place in the cytoplasm of every cell.

What is the starting molecule for glycolysis?

Energy pulled from the method of glycolysis is not so much however it is the starting point of cellular respiration or respiration cells. It occurs every time and each second in all cells even in cancerous cells.

This is true for both prokaryotes and eukaryotes. It happens in both aerobic and anaerobic respiration cells.


Where does glycolysis take place in the eukaryotic cells?

Glycolysis occurs from the cytoplasm.


Aerobic respiration occurs in mitochondria, whereas anaerobic respiration occurs in the cytoplasm.

Glycolysis is Common to both aerobic and anaerobic respiration.

Glucose (C6H12O6)is transformed into 2 molecules of pyruvic acid (CH3COCOOH)


In aerobic respiration, pyruvic acid is converted into acetyl coenzyme that enters the lactic acid cycle in the mitochondrion.


Where does glycolysis occur?

Canonically, Glycolysis occurs in the cytoplasm of eukaryotic cells.

Glycolysis anaerobic or aerobic – Is glycolysis aerobic or anaerobic

Uptake of glucose Or metabolic conversion of other compounds to sugar results in elevated sugar levels in the cytoplasm. In glycolysis for each molecule of glucose oxidized to pyruvate. 1 molecule of glucose undergoes hydrolysis to form 2 molecules of pyruvate, and in doing this, charges two molecules of ADP (adenosine diphosphate) with energy.


What is ATP and how is it produced?

This energy is stored in additional phosphate bonds, forming ATP (adenosine triphosphate). These are used for energy, and also the rest of the pyruvate could experience breakdown to form an acidic chemical in the absence of oxygen or carbon dioxide in the presence of oxygen. That process is continued out from the mitochondria.

In anaerobic respiration, pyruvic acid is transformed either into lactic acid or ethyl alcohol(C2H5OH) and CO2 in the cytoplasm.



How does ADP become ATP?

Can ATP can convert to ADP during dephosphorylation

Yes, it can, during dephosphorylation

What is the glucose source?

The simple glucose source is from “foods high in glucose”. Means, the food products which are high in glucose are the easiest way to get glucose.

Some of these sources of glucose are –

  • Carbohydrate: Includes potatoes, vegetables, fruit, bread, rice, pasta, sugar, yoghurt, and milk. Our bodies convert 100 per cent of the carbohydrate into glucose that we eat.
  • Protein: Includes meat, cheese, fish and peanut butter.
  • Fat: Includes avocado, butter, salad dressing and olive oil.

How does ATP turn into ADP?


Adp molecule (adenosine diphosphate)

-ATP is a vital molecule that acts as a supply of cellular energy that’s wont to drive cellular processes. It conjointly acts as a storage molecule of energy for future use.

-For a molecule of adenosine triphosphate to unharness energy that’s held on within the phosphate bonds, it’s dephosphorylated to ADP and orthophosphate.

That is; adenosine triphosphate = ADP + Pi (inorganic phosphate).

-Dephosphorylation involves the removal of a phosphate (PO43−) cluster from the associate compound by the reaction.


How many NADH are produced by glycolysis?

Glycolysis is the Initial measure of cellular respiration. This procedure breaks down blood into two pyruvic acids, this glycolysis process happens in the cytoplasm of the cell and produces 2 ATP and 2 NADH.



After Glycolysis, which happens from the cytoplasm, out of the mitochondrion, The remainder of cellular respiration occurs inside of the mitochondrion.

Glycolysis breaks down glucose, in reactions producing pyruvic acid (pyruvate), adenosine triphosphate (ATP), reduced nicotinamide adenine dinucleotide (NADH), protons (hydrogen ions (H++)), and water (H22O).

For details, Wikipedia article Glycolysis is quite good.


Catabolic definition

Catabolism is the part of the metabolism responsible for breaking complex molecules, high energy molecules, down into smaller particles. The other a part of the metabolism, anabolism, builds simple molecules into more complex ones. During catabolism, energy is released from the bonds of the large molecules being broken down. Typically, that energy is then kept within the bonds of nucleotide (ATP).

The organic process will increase the concentration of adenosine triphosphate within the cell because it breaks down nutrients and food. The ATP, at such high levels, becomes much more likely to give up its energy in the release of phosphate. The anabolism then uses this energy to combine simple precursors into complex molecules that add to the cell and store energy for cell division.


Definition of cytoplasm

The cytoplasm includes the organelles. The “jelly-like substance” that surrounds organelles in the cytosol. The cytoplasm is anything within the cell membrane not including the nucleus. They are often confused for one another.

Thioester bond

Thioester‐linkage is a labile ester‐bond between the COOH‐group of carboxylic acid and a ‐SH‐group of an amino acid residue within the peptide chain (S‐Acylation). An ester‐type linkage may be by experimentation experiment} distinguished from an organic compound bond by treatment of the acylated supermolecule with hydroxylamine. This compound cleaves ester‐linked fatty acids from the supermolecule, whereas amide‐linked fatty acids aren’t affected.


What is phosphate?

Phosphate is classified into several groups which are based on the number of phosphorus (P) molecules. Each group have functional properties as mentioned below for many applications.


Orthophosphates  Buffering – detergents
Pyrophosphates  Sequestering – water treatment, metal cleaning
Tripolyphosphates  Dispersant – meat processing, dish detergent
Polyphosphates  Dispersant – kaolin production


Number of P Atoms Ion Usual Name
1 PO4-3 Orthophosphates
2 P2O7-4 Pyrophosphates
3 p3O10-5 Tripolyphosphates
> 3 PnO(3n+1)-(n+2) Polyphosphates

Glycolysis pathway or Glycolytic pathway

Glycolysis Chart
Glycolysis Chart

What are the steps of glycolysis

Glycolysis Explained in 10 Easy Steps

  • Hexokinase
  • Phosphoglucose Isomerase
  • Phosphofructokinase
  • Aldolase
  • Triosephosphate isomerase
  • Glyceraldehyde-3-phosphate Dehydrogenase
  • Phosphoglycerate Kinase
  • Phosphoglycerate Mutase
  • Enolase
  • Pyruvate Kinase


What are the products of glycolysis?

Is glycolysis aerobic

Phase 1 glycolysis – Glycolysis is the First phase of aerobic respiration. It happens in the cytoplasm and doesn’t need oxygen.

Glycolysis products involve two Chief steps catalyzed by enzymes in the cytoplasm:

1 Breakdown of Glucose to triose phosphate

Glucose is first Activated by phosphorylation, i.e., the addition of phosphate groups. ATP provides the phosphate. During the procedure, two molecules of ATP are utilized, and a sugar molecule is broken down into two molecules of triose phosphate. In other words, before energy is released by respiration, power is necessary to initiate the reactions.

 2 Oxidation of triose phosphate to pyruvate

Glucose to pyruvate

Next, each triose Phosphate molecule is oxidized to a 3-C compound known as pyruvate. A total of two molecules are formed of ATP, and triosephosphate becomes oxidized (loses hydrogen) . A carrier molecule Named NAD accepts the hydrogen.

(nicotinamide adenine dinucleotide). Because of this, NAD is reduced to form NADH. NADH will act as a hydrogen donor· at the last stage of respiration to make more ATP.


What is pyruvate?

Pyruvate definition

Pyruvate is a crucial molecule that’s a gift at the intersection of multiple organic chemistry pathways. It is commonly encountered as one of the end product of glycolysis, which is then transported to the mitochondria for participating in the citric acid cycle.

In the absence of gas, or when oxygen demand outstrips supply, pyruvate can undergo fermentation to produce lactate. Both pyruvate and nurse is wont to regenerate aldohexose still. Pyruvate can also be involved in the anabolic synthesis of fatty acids and amino acids.

There is also growing evidence that it can directly influence nuclear activity and epigenetic modifications, forming the interface between the genome and the metabolic state of the cell.

Glycolysis mnemonic

Pumpkin pie – one of my absolute favorite things!

Memorizing biochemistry pathways – um, not quite as high on the favorites list.

Joining the two = a palatable combination!

As you are enjoying your holiday desserts, try out these mnemonics to remember the steps of glycolysis:


“Goodness Gracious, Father Franklin

Did Go By Picking Pumpkins (to) PrEPare Pies”

  • Glucose
  • Glucose-6-Phosphate
  • Fructose-6-Phosphate
  • Fructose-1,6-diPhosphate
  • Dihydroxyacetone-Phosphate
  • Glyceraldehyde-Phosphate
  • 1,3-Biphosphoglycerate
  • 3-Phosphoglycerate
  • 2-Phosphoglycerate 
  • Phosphoenolpyruvate [PEP] Pyruvate
  • PyruvateSome Facts About Glycolysis:
  • Glycolysis is also referred to as EMP ( Embden Meyerhof Parnas) pathway.
  • It is a common pathway for both aerobic and anaerobic respiration.
  • It occurs in the cytoplasm.


Irreversible steps of glycolysis
Irreversible steps of glycolysis


Substrate-Level Phosphorylation

Substrate-level phosphorylation is the preferred route invoked to synthesize energy in order to compensate for ineffective ATP-generating machinery observed in the presence of elevated amounts of RNS.

From: Microbial Diversity in the Genomic Era, 2019


Difference between Glycolysis Cycle and Kreb’s Cycle

Glycolysis is the first step in the method of energy production from a sugar molecule, which ends with the creation of two molecules of pyruvate, which then gets converted to citric acid and enters the citric acid cycle also called Kreb’s cycle for further production of energy.


          GLYCOLYSIS CYCLE                              KREB’S CYCLE
The reactant is one molecule of glucose The reactant is pyruvate which gets converted to citric acid which then enters the cycle
The product is 2 molecule of pyruvic acid Pyruvate is oxidised to carbon dioxide and water
It occurs in the cytoplasm of a cell It occurs in the mitochondria of a cell
It can take place both aerobically and anaerobically It can take place only in the presence of oxygen
8 ATP molecules produced 24 ATP molecules produced
2 NADH molecules produced 6 NADH and 2 FADH2 molecules produced



“Glycolysis” is the anaerobic process in which one molecule of glucose (C6H12O6) is oxidized to create two molecules of pyruvic acid. The particles of pyruvic acid can further engage in Kreb’s Cycle or fermentation.

Glycolysis takes place in the cytosol
Glycolysis takes place in the cytosol



To have the Procedure Further explained:

 Glucose→two Phosphoglyceraldehyde (PGAL)→two Pyruvic Acid


The Procedure Generates 4 Adenine Triphosphate (ATP) and 2 NADH and uses 2 ATPs. So internet manufacturing is just 2 ATPs and 2 NADH. Keep in mind that they are generally regarded as”bonuses”: they are energy obtained in the process of the creation of pyruvic acid molecules.

 However, in the old Ages, when there was little oxygen in our earth’s atmosphere, these bonuses were the predominating resources of energy. At the evolution of the planet, the presence of oxygen later led to another efficient method of rendering power by putting the pyruvic acid molecules in further use (that the Kreb’s cycle).

 To reiterate, glycolysis is a dominant pathway to yield energy without any intakes of oxygen. However, glycolysis is not efficient: it generates too few ATPs.


*UPDATE: I’d state that the”primary products” are pyruvic acid molecules, and the”secondary goods” are ATPs and NADH.

 The goods of glycolysis are two pyruvates, four reduced NAD, and 2 ATPs.


hexose biphosphate



 ATP = Adenosine Tri-Phosphate

 TP is Glyceraldehyde 3-Phosphate and may also be called GALP/GADP/G3P/PGAL.

 NAD = Nicotinamide Adenine Dinucleotide


What is NADH?

Nadh, nad, definition


Abbreviation for nicotinamide adenine dinucleotide

Whats NADnicotinamide adenine dinucleotide

(NAD) carrying two electrons and bonded with a hydrogen (H) ion; the reduced form of NAD

NADH2 means reduced NAD. (Sometimes reduced can also be written as NADH)

ETC = Electron Transport Chain

Glycolysis, also Known as the Embden-Meyerhof pathway, is described as starting with sugar and ending with two pyruvates plus joint production of two ATP. However, It’s vital to look at a whole balanced equation, which we could later shorten for convenience:


Where do the first 2 ATP come from during cellular respiration
Where do the first 2 ATP come from during cellular respiration



Glucose + 2 Pi + 2 ADP + 2 NAD+ →

 2 Pyruvate + 2 ATP + 2 NADH + 2 H+ + 2 H2O

 The excellent Goods are pyruvate, ATP, and NADH.


Conversion of Glucose to two pyruvates is a web oxidation glycolysis reaction, and that’s why NAD has involved. Oxidation of glucose occurs via dehydrogenation, producing NADH. It is crucially important to understand that the quantity of NADH generated equal the amount of pyruvate. Under anaerobic conditions, these unite stoichiometrically to form lactate (in humans and other animals), so the net equation is


Where does glycolysis occur
Where does glycolysis occur




Glucose + 2 Pi + 2 ADP → 2 lactate + 2 ATP + 2 H2O

With no Decline of NAD, glycolysis could not run for long under anaerobic conditions.

 Although the yield of ATP may seem low, the pathway can run very fast, producing ATP rapid enough to Encourage life anaerobically and contribute substantially to extreme exercise. Many of the cells of the body utilize anaerobic glycolysis as a principal energy source. Red blood cells use it exclusively.




What is the glycolysis equation?

Glycolysis equation

The simplified equation for glycolysis is: C6H12O6 + 2 NAD+ + 2 ADP + 2 P —–> 2 pyruvic acid, (CH3(C=O)COOH + 2 ATP + 2 NADH + 2 H+. Glycolysis is a series of biochemical reactions that break down a glucose molecule into two molecules of pyruvic acid.

Cells use oxygen to release energy during exercise?

What happens when you exercise? The harder you exercise the more fuel or glucose your cells must burn. More oxygen is used by the cells if your cells burn more glucose. So it’s obvious that the cells need to get more fuel or glucose and oxygen to continue exercising.

At the same time, the cells must get rid of all the carbon dioxide they are producing as you continue to exercise. That’s the reason your heart beats faster and your lungs move more air in and out when you exercise. Your heart and lungs are keeping up with the demands of your cells. Engineers admit that they couldn’t design a more efficient system than the heart and lungs. Our hearts and lungs, like many other animals’ hearts and lungs, work to match the flow of blood and gas to the needs of the cells.

When the cells need more fuel and oxygen and need excess CO2 removed, the heart and lungs work harder than when the cells need less.


What is the number of ATP gained in glycolysis?

Preparatory Phase (Phase 1 glycolysis):

  1. Initially Priming Reaction, Glucose -> Glucose 6- Phosphate, one molecule of ATP is used.
  2. In the second Priming Reaction, Fructose 6- phosphate -> Fructose 1,6-bisphosphate, one molecule of ATP is utilized.

Total ATP Consumption: 2 molecules

Payoff phase of glycolysis:

  1. First ATP-forming Reaction (Substrate Amount Phosphorylation), 1,3 bisphosphoglycerate -> 3 phosphoglycerate,2 molecules of ATP are formed.
  2. Second ATP- forming Reaction (Substrate Amount Phosphorylation), Phosphoenolpyruvate -> Pyruvate, two molecules of ATP are formed.


Complete ATP Production: 4 molecules


Web Yield : 4 ATP – 2 ATP = 2 ATP molecules


  1. In addition to It, Oxidation and Phosphorylation of Glyceraldehyde 3-phosphate -> 1,3 – bisphosphoglycerate is included. In this step, two NAD molecules are absorbed to form 2 NADH molecules.


Therefore, two NADH Molecules = 6 ATP molecules.

Hence, Internet Energy Yield in Glycolysis

= 2 ATP + 6 ATP=8 ATP molecules


Anaerobic glycolysis

In Anaerobic Glycolysis,

Gain is only of two ATP molecules


Aerobic glycolysis

In Aerobic Glycolysis,

Net gained ATP = 2 ATP molecules

Gross gained ATP = 8 ATP molecules



Every 1 ATP molecule is Gained in due to:-


  1. 1,3-biphosphoglycerate to 3-phosphoglycerate


  1. PhosphoenolPyruvate To Pyruvic acid


1 NADH2 molecule is Gained that’s equal to 6 ATP molecules in the conversion​ of


  1. Glyceraldehyde to 1,3-biphosphoglycerate

Important Terms in Glycolysis
Important Terms in Glycolysis


What is cellular respiration?

Cellular respiration definition

Definition of cellular respiration – Cellular respiration is the process where the result is diverting the chemical energy where organisms combine oxygen with foodstuff molecules in these substances into life-sustaining activities and discarding, as waste products, carbon dioxide, and water. Plants that do not depend on oxygen degrade foodstuffs in a process called fermentation.


In cell respiration, 36 ATPs are produced in Aerobic Respiration involving the complete breakdown of a glucose molecule into carbon dioxide and water using oxygen as final electron acceptor


How is 36 ATP produced?

The oxidation of glucose molecule takes place in 3 types of sequential reactions –

1.Glycolysis occurring in the cytoplasm

2.Kreb cycle occurring in the mitochondrial matrix

3 Electron transport chain (ETC )and oxidative phosphorylation occurring in the inner mitochondrial membrane.



In glycolysis, if we see the overall reaction, 1 glucose molecule is converted into two molecules of pyruvate with the release of 2 molecules of NADH2 (Nicotinamide adenine dinucleotide -reduced form) a total of 4 ATPs get synthesized by substrate-level phosphorylation (SLP).


As we know, NADH2 molecule will enter ETC, and from 1 molecule of NADH2, 3 or 2 ATPs are synthesized depending upon the shuttle system operating , the system transfer the NADH2 synthesized in cytoplasm to the mitochondrial matrix so that they can enter ETC and finally undergoes oxidative metabolism phosphorylation leading to the production of ATPs.


There are two types of shuttle systems operating in the cell, I’m not going into too much detail but remember that one shuttle system leads to the production of 2 ATPs while other produce 3 ATPs per NADH2 molecule.


And moreover, in the first two reactions of glycolysis, 2 ATPs are used, so there is a net gain of only 2 ATPs through SLP.


The oxygen consumed during cellular respiration is involved directly in which process or event?

a) Glycolysis.

b) Accepting electrons at the end of the electron transport chain.

c) The citric acid cycle.

d) The oxidation of pyruvate to acetyl CoA.

e) The phosphorylation of ADP to form ATP.

The answer is “Accepting electrons at the end of the electron transport chain”.



In the presence of oxygen, pyruvate will enter the link reaction that occurs in the mitochondrial matrix and connects glycolysis with the Kreb cycle. In link reaction, two pyruvate molecules undergo oxidative decarboxylation to form 2 molecules of acetyl-CoA with the release of carbon dioxide and two molecules of NADH2.


After this, two molecules of acetyl-CoA enters the Kreb cycle and undergo complete oxidation leading to the release of 2 FAD molecules ( flavin dinucleotide), six molecules of NADH2 and 2 ATPs /GTPs by SLP.


2 ATPs are produced, from 1 molecule of FAD. So total ATPs produced in the link, and Kreb cycle is


Total 8 NADH2 -24ATPs (No shuttle system operates as a link, and kreb cycles operate within the mitochondrial matrix)



Total ATPs – 30 ATPs

So, the total number of ATPs produced in aerobic respiration is

Glycolysis – 6/8 ATPs

Link reaction and Kreb cycle – 30ATPs

Total -36/38 ATPs


How many ATP are produced by 1 glucose in aerobic respiration?

One crucial factor is that we want to use the ATP in the cytoplasm, so for any ATP produced in the matrix, there is an additional cost of 1 proton from the gradient associated with the import of ADP+Pi and export of ATP.

  1. Glycolysis consumes one glucose and produces 2 ATP, 2 NADH, and two pyruvates. This ATP is already in the cytoplasm, so no transport required. However, the NADH is also in the cytoplasm, and if we want to use them for ox phos, they (or rather their reducing equivalents) have to get into the matrix. If this occurs by the glycerol phosphate shuttle, the electrons enter the ETC at the level of ubiquinone, and their transport to O2 pumps only 6 H+/2e. If they enter via the malate-aspartate shuttle, they come as NADH, and their oxidation will pump 10 protons/2e-. So this leads to an uncertainty 12 vs. 20 H+ for the NADH from glycolysis. For book-keeping purposes, we will assume the use of the mal/asp shuttle and include a variable cost of 0 to -8 protons lost if the GP shuttle is used instead. The two pyruvates must also be translocated into the matrix by pyruvate translocase, at the cost of one H+ each.


Start a balance sheet:

  1. step G/ATP   NADH    UQH2   H+gradient
  2. glycolysis 2      2        0     0 to -8(use of GP shuttle)
  3. Pyruvate dehydrogenase complex converts those 2 pyruvates to two Acetyl CoA, producing also 2 NADH (in the matrix)
  4. PDC:2                     -2   (transport of
  5. pyruvate into the matrix)
  6. The TCA cycle consumes 2 acetyl-CoA and produces 2 ATP(equivalent), 2×3 NADH, and 2×1 UQH2 oth ATP which are made in the matrix will require 1 H+ each to bring in ADP+Pi and export ATP

2xTCAC 2 6 2 -2 in order to export ATP

  1. ETC- now oxidize the NADH and UQ2 via the Electron Transport Chain:
    The currently accepted H+/2e ratios I think were summarized by P.Hinkle (2005)*. Oxidation of NADH transports 10 protons (4+2+4) out of the matrix, oxidation of UQH2 transports 6 (2+4).

Adding up from above:

  1. step        G/ATP  NADH   UQH2  H+gradient
  2. 1 glycolysis:2      2       0    0 to -8(use of GP shuttle)
  3. 22×PDC:2              -2(transport of pyruvate)
  4. 32×TCAC:2      6       2      -2 to export the ATP
  5. 4 ETC:              -10      -2    +112(10×10+6*2)
  6. ———————————————————-
  7. cumul sum:4      0       0    100 to 108 depends on shuttle


Answer: 31.3 to 33.5 ATP/glucose.


Glycolysis assay kit

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Glycolysis summary

Summary of glycolysis –

The breakdown of a Glucose molecule into two molecules of triose phosphate absorbs two molecules of ATP. The oxidation of these two molecules of triose phosphate forms four molecules of ATP. Therefore, glycolysis generates a net amount of 2 molecules of ATP.


  • Watt et al. (2010) Bioenergetic cost of making an adenosine triphosphate molecule in animal mitochondria.
  • Zhou et al. (2015) Structure and conformational states of the bovine mitochondrial ATP synthase by cryo-EM.
  • Peter C. Hinkle (2005) P/O ratios of mitochondrial oxidative phosphorylation.
  • PH Raven, RF Evert, SE Eichhorn (1987). Biology of Plants. Worth Publishers.
  • Editors of Encyclopedia Britannica (2019). Glycolysis. Retrieved from
  • RL Dorit, WF Walker, RD Barnes (1991). Saunders College Publishing.
  • Editors of Encyclopedia Britannica (2019). Cellular respiration. Retrieved from
  • Editors of Encyclopedia Britannica (2019). Tricarboxylic acid cycle. Retrieved from
  • Jonathan G. Best, … Andrea Dennis, in Magnetic Resonance Spectroscopy, 2014
  • Patrick F. Chinnery, Douglass M. Turnbull, in Neurology and Clinical Neuroscience, 2007

Glycolysis biochemistry PDF



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