Glycolysis: Explained.
Glycolysis.
- Glycolysis the term is derived from two words, Glyco (Glucose) and Lysis (Breakdown), and hence glycolysis is nothing but the breakdown of a glucose molecule to gain the energy.
- A body gets its energy from the breakdown of many biomolecules, carbs, fats, and proteins, chiefly from carbs.
- The body uses its energy in the form of ATP (Adenosine tri Phosphate), in glycolysis, the glucose molecule is broken down to get ATPs.
- Glycolysis involves nine reactions that convert glucose into pyruvate.
- All of the glycolytic enzymes are found in the cytosol.
Step 1: Conversion of glucose to glucose-6-phosphate.
- In the first step of glycolysis, the glucose ring is phosphorylated by addition of a phosphate to the glucose ring.
- The reaction is catalyzed by enzyme "Hexokinase" with Mg ion.
- The "Kinase" are a group of enzymes that catalyze the "phosphorylation" reactions, the Hexokinase catalyzes phosphorylation of many six membraned rings.
- One ATP is consumed in this process.
- The reaction results in the formation of Glucose-6-Phosphate.
- Glucose (C6H12O6) + hexokinase + ATP → ADP + Glucose 6-phosphate (C6H13O9P)
Step 2: Conversion of Glucose-6-Phosphate to Fructose-6-Phosphate.
- In the second step, the formed Glucose-6-Phosphate is get converted into its isomer i.e. Fructose-6-Phosphate.
- This reaction is called as isomerization is catalyzed by enzyme "Phosphoglucose Isomerase (Phosphofructo isomerase)".
- This reaction pulls out one carbon out from the ring.
- The reaction results in the formation of fructose-6-Phosphate.
- Glucose 6-phosphate (C6H13O9P) + Phosphoglucoisomerase → Fructose 6-phosphate (C6H13O9P)
Step 3: Conversion of Fructose-6-Phosphate to Fructose 1-6- biphosphate.
- In the third step of glycolysis, fructose-6-phosphate is converted to fructose- 1,6-biphosphate.
- In this reaction, one molecule of phosphate is added.
- The reaction is catalyzed by "Phosphofructo Kinase" with Mg ion.
- One ATP is consumed in this step.
- This reaction results in the formation of Fructose-1-6-biphosphate.
- Fructose 6-phosphate (C6H13O9P) + phosphofructokinase + ATP → ADP + Fructose 1, 6-bisphosphate (C6H14O12P2)
Step 4: Cleavage of Fructose-1-6-biphosphate to Glyceraldehyde-3-phosphate and Dihydroxyacetone Phosphate.
- In this reaction, the Fructose 1-6-biphosphate a six carbon compound is get cleaved into 2 three carbon compounds namely glyceraldehyde-3-phosphate and dihydroxyacetone phosphate.
- The reaction is catalyzed by enzyme "Aldolase"
- The formed dihydroxyacetone phosphate is unstable and gets reorganized to glyceraldehyde-3-phosphate immediately by the action of the enzyme "triphosphate isomerase".
- Hence the glyceraldehyde-3-phosphate continues the cycle.
- Fructose 1, 6-bisphosphate (C6H14O12P2) + aldolase → Dihydroxyacetone phosphate (C3H7O6P) + Glyceraldehyde phosphate (C3H7O6P)
- Dihydroxyacetone phosphate (C3H7O6P) → Glyceraldehyde 3-phosphate (C3H7O6P)
Step 5: Conversion of glyceraldehyde-3-phosphate to 1-3-biphospho glycerate.
- In this step, two main events take place:
- 1) Glyceraldehyde-3-phosphate is oxidized by the coenzyme nicotinamide adenine dinucleotide (NAD); to give NADH+H this NADH+H after entering ETC (Electron Transport Chain) produces 3 ATPs.
- 2) The molecule is phosphorylated by the addition of a free phosphate group.
- The enzyme that catalyzes this reaction is glyceraldehyde-3-phosphate dehydrogenase (GAPDH).
- This reaction produces 6 ATPs. (Two Glyceraldehyde-3-phosphate molecules)
- The reaction results in the formation of 1-3-biphospho glycerate.
A. Triose phosphate dehydrogenase + 2 H- + 2 NAD+ → 2 NADH + 2 H+B. Triose phosphate dehydrogenase + 2 P + 2 glyceraldehyde 3-phosphate (C3H7O6P) → 2 molecules of 1,3-bisphosphoglycerate (C3H8O10P2)
Step 6: Conversion of 1-3 biphosphoglycerate to 3-phosphoglycerate.
- In this step, 1,3 bisphoglycerate is get converted to 3-phosphoglycerate.
- The reaction is catalyzed by enzyme "phosphoglycerate kinase" with Mg ions.
- The enzyme family "Kinase' deals with the transfer of ATP, the Mg (Magnesium) ion helps to shield the negative charges.
- Two ATP is synthesized in this step. ( As Dihydroxyacetone phosphate is get converted immediately to Glyceraldehyde-3-phosphate, we get two molecules of Glyceraldehyde-3-phosphate)
- The reaction results in the formation of 3-Phosphoglycerate.
- 2 molecules of 1,3-bisphoshoglycerate (C3H8O10P2) + phosphoglycerokinase + 2 ADP → 2 molecules of 3-phosphoglycerate (C3H7O7P) + 2 ATP
Step 7: Conversion of 3-phosphoglycerate to 2-phosphoglycerate.
- This reaction causes structural rearrangement of 3-phosphoglycerate forming
2-phosphoglycerate. - The enzyme which catalyzes the reaction is "Phosphoglycerate Mutase."
- The enzyme family "Mutase" carries out the function of transferring the functional groups from one position to another.
- The reactions result in the formation of 2-phosphoglycerate.
- 2 molecules of 3-Phosphoglycerate (C3H7O7P) + phosphoglyceromutase → 2 molecules of 2-Phosphoglycerate (C3H7O7P)
Step 8: Conversion of 2-phosphoglycerate to Phosphoenolpyruvate.
- This step involves the conversion of 2-phosphoglycerate to phosphoenolpyruvate.
- The reaction is catalyzed by the enzyme enolase.
- Enolase works by removing a water group or dehydrating the 2- phosphoglycerate.
- The reaction results in the formation of "Phosphoenolpyruvate"
- 2 molecules of 2-Phosphoglycerate (C3H7O7P) + enolase → 2 molecules of phosphoenolpyruvate (PEP) (C3H5O6P)
Step 9: Conversion of Phosphoenolpyruvate to Pyruvate.
- In this step, phosphoenolpyruvate is get converted into pyruvate.
- The enzyme that catalyzes this reaction is "Pyruvate kinase".
- As the enzyme name suggests the reaction involves the transfer of ATP molecule, one ADP (Adenosine triphosphate) is getting converted to one ATP.
- The reaction results in the formation of Pyruvate and 2 ATPs.
- All above reactions take place in an "aerobic environment (In presence of atmospheric oxygen)".
- If the conditions become "anaerobic (In absence of atmospheric oxygen)" the reaction proceeds to the formation of the "lactic acid".
- 2 molecules of phosphoenolpyruvate (C3H5O6P) + pyruvate kinase + 2 ADP → 2 molecules of pyruvate (C3H3O3-) + 2 ATP
Step 10: Conversion of Pyruvate to Lactate.
- When anaerobic conditions continue as in strenuous exercise, the formed Pyruvate is get converted to Lactate.
- The reaction is catalyzed by the enzyme "Lactate Dehydrogenase.
- Two NADH+H are used in the process.
- The reaction cause loss of 6 ATP molecules.
AFTERMATH:
- We have seen different reactions causing ATPs in and out, now let's see how much ATPs we can gain from the glycolysis.
Outcome
of Glycolysis.
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Loss
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Profit
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Reaction
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Outcome of ATP
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Reaction
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Outcome of ATP
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Step 1: Conversion of glucose to
glucose-6-phosphate.
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1
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Step 5: Conversion of
glyceraldehyde-3-phosphate to 1-3-biphospho glycerate.
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3x2= 6 (Two molecules of
Glyceraldehyde-3-phosphate)
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Step 3: Conversion of
Fructose-6-Phosphate to Fructose 1-6- biphosphate.
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1
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Step 6: Conversion of 1-3 biphosphoglycerate to 3-phosphoglycerate.
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1x2= 2 (Two molecules of
Glyceraldehyde-3-phosphate)
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Step 10: Conversion of Pyruvate to
Lactate.
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3x2= 6 (Two molecules of
Glyceraldehyde-3-phosphate)
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Step 9: Conversion of
Phosphoenolpyruvate to Pyruvate.
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1x2= 2 (Two molecules of
Glyceraldehyde-3-phosphate)
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Total
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08
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Total
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10
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In Aerobic Conditions Glycolysis yields 10-2= 8 ATPs.
In Anaerobic Conditions Glycolysis yields 10-8= 2 ATPs.
Cyclic Representation of Glycolysis:
Labels: Biochemistry
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