Glycolysis Cycle


Degradation of Glucose to Pyruvate


Glycolysis definition:- In all living organisms, the initial phase of respiratory metabolism involves degradation of glucose in to pyruvate. The steps involved in the degradation were studied and explained by three biochemists namely Emden, Meyerhof and Parnas, therefore, it is also called EMP pathway. The enzymes for breakdown of glucose are present in the cytosol (the soluble part of cytoplasm is called cytosol) mainly. Thus, glycolysis is not associated with any particular organelle. The oxygen is not required to convert glucose to pyruvate and some energy is also produced during the process. Therefore, the glycolysis serves as primary means of energy production in plant tissues where oxygen levels are low; for example, in roots growing in water saturated soils (flooded soil).

Glycolytic Pathway – Biochemistry of Glycolysis

It is an oxidation reduction process in which one glucose molecule is broken down in to two molecules of pyruvate acid and net two ATP are produced.

The glucose and fructose can readily enter the pathway. These are derived from the breakdown of either sucrose or starch. Thus, following steps are involved in breakdown of glucose to pyruvate.

Phosphorylation of Glucose

The glucose is phosphorylated to glucose 6-phosphate in the presence of ATP and hexokinase.

Isomerization of Glucose 6-P

The glucose 6-phosphate is isomerized to fructose 6-phosphate by hexose-phosphate isomerase. Phosphorylation of fructose 6-P: Fructose 6-P is phosphorylated to fructose 1,6-bisphospahte in the presence of ATP and enzyme phosphofructokinase.

Cleavage of Fructose 1,6-bisP

Fructose 1,6-bisP is cleavage by two molecules of 3-C isomers which are interconvertible, glyceraldehyde 3-phosphate (phosphoglyceraldehyde) and dihydroxyacetone phosphate.

Dehydrogenation of Glyceraldehyde 3-P

In the presence of ATP and NAD+, the aldehyde group of (-CHO) of glyceraldehyde 3-P is oxidized to carboxyl group (-COOH) to produce 1,3-bisphosphoglyceric acid. The H+ released reduces NAD+ to NADH2.

Dephosphorylation of 1, 3-bisPGA & Formation of ATP

1,3-bisphosphoglyceric acid is converted to 3-phosphoglyceric acid by phosphoglycerate kinase, generating two ATP molecules.

Formation of 3-Phosphoglyceric Acid

1,3-phosphoglyceric acid mutates two 2-phosphoglyceric acid under the catalytic activity of phosphoglycerate mutase.

Formation of Phosphoenolpyruvate

Enolase converts 2-phosphoglyceric acid to phosphoenolpyruvate.

Formation of pyruvate & ATP Generation

Phosphoenolpyruvate (PEP) is converted into pyruvate by pyruvate kinase. Two molecules of ATP are generated during this step.

Glycolysis products

Glycolyses Products are following:-

  • 2 molecules of pyruvate
  • 2 molecules of NADH2
  • 4 ATP molecules Total

two molecules of ATP are consumed during the reaction, therefore, there is net gain of 2 ATP molecules.

Glycolysis Products

Glycolysis Products


Glycobsis is the underlying step of catabolic chemical reactions. It happens practically in every one of the phones. Six-carbon glucose atom is broken do” ii into too particles pyruvate durnig glycolysis. Pyruvate is a three carbon compound. There is net generation ol bi’o molecuces or ATP amid glycolysis. Every particle of glucose item, lour atoms or P amid glycolysis. Be that as it may, to A FP atoms curve used to improve theglucose particle. They frame 11’n,k six-carbon mixes. Along these lines, the net vitality yield from glycolys1; is just two ATP particles. Glycolvsis does not productively collect from glucose. Be that as it may, it was the main to create KIT particles for midions of years amid the anaerobic phases of early life on earth. Folio.% ing reactions happen amid glycolysis:

(an) Energy Investment Phase

I. Step Glucose enters the cell. It is phosphorylated,by the protein

hexoldnase. This protein exchanges a phosphate amass front ATP to the .sugar. The plasma film is impermeable to particles. So the electrical charge of the phosphate aggregate traps the sugar in the cell. Phosphorylation of glucose makes the particle all the more chemically respond is e.

Step 2: Glucose 6-phosphate is revamped by compound isomerase. It is changed over it to its isomer. fructose 6-phosphate

Step 3: In this step, another atom of ATP is utilized as a part of glycolysis. A compound phosphofructokinase exchanges a phosphate gather from ATP to the sugar.

Step 4: This is reaction from which glycolysis gets its name. A compound aldolasethreaks the sugar atom into two distinctive three-carbon sugars: glyceraidehydes phosphate and dilly droxyacetone phosphate. These two sugars are isomers of each other.

5′. Step 5: Another catalyst catalyzes the reversible transformation between the two three—carbon sigars.. The reaction achieves balance in test tube. .[he next protein in glycolysis utilizes just glyceraldehyde phosphate as its substrate.

(b) Energy-Yielding Phase

Step 6: A compound now catalyzes two reactions. In the first place, glyceraldehyde phosphate is oxidized tiw the exchange of electrons and FI to NAD. It shapes NADI I . This reaction is extremely exergonic kcal/mol). The protein utilizes this vitality to append a phosphate gathering to the oxidized substrate. It shapes 1,3 bisphosphogly frightful corrosive The wellspring of the phosphate is inorganic phosphate. It is constantly present in the cytosol.

Step 7: Finally… glycolysis produces sonic An IT. The phosphate gather included the past step is exchanged to ADP. It break 1,3 bisphosphoglyeeric corrosive to shape 3 phosithogi) minister. This compound is not a sugar. The carbonyl gathering that portrays a sugar has been oxidized to a carboxyl gathering. It is an org:mic corrosive.

–8. Step 8: A protein mutase moves the rest of the phosphate


gathering. It shapes 2-phosphoglycerate. It readies the substrate for the following reaction.

Step 9: A catalyst enolase evacuates a water atom and shape a twofold security in the substrate. It shapes phosphoenol pyruvate. or, on the other hand PEP. This makes the substrate extremely temperamental.

Step 10: A catalyst pyruvate kinase exchanges the phosphate bunch from PEP to ADP. So it creates more ATP. Since this step happens twice for every glucose particle, so there is a net pick up of two ATP atoms. Consequently glucose has been separated and oxidized to two particles of pyruvate. It is the final result of the glycolytic pathway

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