GLYCOLYSIS

GLYCOLYSIS

INTRODUCTION TO GLYCOLYSIS

Glycolysis is from the greek glycos,sugar and lysis breakdown is the pathway that partially catabolizes carbohydrate primarily glucose that involve the anaerobic and aerobic respiration.

Glucose that contain 6 carbon molecules it converted into two three carbon It enters cells through specific transporter proteins that move it from outside the cell into the cell’s cytosol. All of the glycolytic enzymes are found in the cytosol.

The overall reaction of glycolysis which occurs in the cytoplasm is represented simply as:

            C6H12O6 + 2 NAD+ + 2 ADP + 2 P —–> 2 pyruvic acid,                           (CH3(C=O)COOH + 2 ATP + 2 NADH + 2 H+

DIAGRAM GLYCOLYTIC PATHWAY

 

STEP 1: HEXOKINASE

Glucose is entered into the cell and phosphoryaleted by the enzymes called hexokinase which transfer the phosphate group  from ATP to the sugar that attach into the carbon six.The charge of phosphate group traps the sugar in the cell because the plasm  membrane is impermiable to ions.Phosphorylation also makes glucose more chemical reactive,This diagram show the tansfer of phosphate group or pear of electron from one reactant to onather.

 

STEP 2:PHOSPHOGLUCOSE ISOMERASE

This is another enzyme that is used to make glucose 6 phosphate is rearranged to convert it to its isomer fructose 6 phosphate.The reaction involves the rearrangement of the carbon­oxygen bond to transform the six ­membered ring into a five ­membered ring. To rearrangement takes place when the six ­membered ring opens and then closes in such a way that the first carbon becomes now external to the ring.

 

STEP 3:PHOSPHOFRUCTOSE

This enzymes it transerfer a phosphate group from ATP to the sugar investing another molecules of ATP in glycolysis so far the ATP ledger shows a debit of 2 with phosphate group on its opposite end sugar is know to split in half where the phosphate it will be attached to the C-1 and C-6 so as to form 1,6 bisphosphate.

STEP 4:ALDOLASE

This reaction from which glycolysis gets its name the enzymes cleaves the sugar molecules into two different three carbon sugar which is glyceraldehyde-3-phosphate and dihydroxycetone.This two sugar are the isomer of each other.

STEP 5:TRIPHOSPHATE ISOMERASE

Isomers catalyzer the reversible conversion between the two -three carbon sugar.This reaction never reaches equilibrium in the cell because the next enzyme in the glycolysis uses only glyceraldehydes-3-phosphate as its substrate and not dihydroxyacetone phosphate.This pulls the equilibrium  in the direction  of glyceraldehydes-3-phosphate which removed fast as it forms.Thus the net  result of step 4 and 5 is cleavage of six carbon sugar into two molecules of glyceraldehydes-3-phosphate each will progress through the remaining step of glycolysis

 

STEP 6: TRIOSE PHOSPHATE DEHYDROGENASE

This enzyme catalyzes the two sequential reaction while it hold glyceraldehydes-3-phosphate in active site.The first sugar is oxidized by the transfer the electrons and H ions to NAD ions (nicotinamide adenine dinucleotide, 2) forming NADH (redox reaction ).This reaction is very exergonic and the enzyme uses the released energy to attach phosphate group to oxidized substrate making a product of very potential energy .The source of phosphate is the pool of inorganic phosphate ions that are

always present in cytosol notice that the coefficient 2 precedes ,all molecules in the energy payoff phase these steps occur after glucose is split into two carborn three sugar in step 4.The phosphate group then attacks the GAP molecule and releases it from the enzyme to yield 1,3 bisphoglycerate, NADH, and a hydrogen atom.

 

STEP 7: PHOSPHOGLYCEROKINASE

Glycolysis finally produce some ATP.The phosphate group added in previous step is transferred to ADP in an exergonic reaction for each glucose molecules that began glycolysis step 7 produces two molecules of ATP since every product after the sugar splitting step 4 is doubled. Since two ATPs were invested to get sugar ready for splitting the ATP ledger is now zero. Glucose has been converted  to two molecules of 3-phosphoglycerate which is not sugar. The carbonxly group the hall mark of an-organic acid, the sugar is oxidized in step 6 and now energy made available by that oxidation has been used to make ATP. 

 

STEP 8:PHOSPHOGLYCERATE MUTASE

This step involves a simple rearrangement of the position of the phosphate group on the 3 phosphoglycerate molecule, making it 2 phosphoglycerate. The molecule responsible for catalyzing this reaction is called phosphoglycerate mutase (PGM). A mutase is an enzyme that catalyzes the transfer of a functional group from one position on a molecule to another.The reaction mechanism proceeds by first adding an additional phosphate group to the 2′ position of the 3 phosphoglycerate. The enzyme then removes the phosphate from the 3′ position leaving just the 2′

 

STEP 9: ENOLASE

This enzymes causes bond to form in substrate by extracting water molecules converting 2-phosphoglycerate to phosphoenolpyruvate (PEP) The electron of substrate are rearranged in such way that remaining phosphate bond become very unstable preparing the substrate for next reaction. Hence the enolase working by removing water group. 

STEP 10: PYRUVATE KINASE

The final step where by phospoenolpyruvate into pyruvic acid with help of  pyruvic kinase which involve the transfer of a phosphate group. The phosphate group attached to the 2′ carbon of PEP  produce more ATP by transferring the phosphate group from (PEP) to ADP since this step occurs twice for each glucose molecules the ATP  ledger now shows a net gain of two ATPs a debt of two ATP was incurred from step 1 and 3 but step 7 and 10 each produced two ATPs for total credit of four glycolysis has repaid the ATP investment with 100% interest. Additional was stored by step 6 in NADH which can be used to make ATP by oxidative phosphorylation if oxygen is present. Glucose has been broken down and oxidized to two molecules of pyruvate the end product of the glycolytic pathway.

 

CONCLUSION

Glycolytic pathway can be produced under the various condition as final product especially under aerobic condition where by pyruvate are produced as well as under anaerobic condition where lactate are produced.Hence the net ATP production are 2 formed directly per molecules of glucose entering pathway can be produced in absence of oxygen.

Coenzyme production 2NADH + 2H+ under aerobic condition

Net reaction (Aerobic: Glucose + 2ADP + 2Pi + 2NAD + —–>2pyruvate  + 2ATP +2 NADH +2H+ + 2H2O

Anaerobic ( Glucose + 2ADP +2Pi—–>2 lactate + 2 ATP + 2H2O