Question

Define glycolysis and the steps of glycolysis

Answer 1

Glycolysis is a stepwise process by which one molecule of glucose which is a six carbon compound breaks down into two molecules of pyruvic acid or pyruvate which is a three carbon compound.
This process was given by GUSTAV EMBEDEN , OTTO MEYERHOF , J PARNAS so it is also called as EMP pathway.
Glycolysis occurs in the cytoplasm of the cell.
It is a common pathway for both aerobic and anaerobic respiration.
STEPS OF GYCOLYSIS ARE GIVEN BELOW:-
1 phosphorylation of glucose occurs under the action of an enzyme hexokinase that gives rise to glucose 6 phosphate by the utilisation of ATP.
2 isomerization of this phosphorylated glucose 6 phosphate takes place to form fructose 6 phosphate with the help of an enzyme for phospho hexose isomerase this is a reversible reaction.
3 this fructose 6 phosphate is again phosphorylated by ATP in order to form Fructose 1 6 bisphosphate in the presence of an enzyme phosphofructokinase.
4 splitting of fructose 1 6 bisphosphate takes place to 2 triose phosphate molecule - first dihydroxyacetone 3 phosphate and second 3 phosphoglyceraldehyde this reaction is catalyzed by an enzyme aldolase.
5 each molecule of phosphoglyceraldehyde remove two redox equivalent in the form of hydrogen atom and transfer them to a molecule of energy NAD+ this NAD+ forms NADH + H + this reaction in turns lead to the conversion of phosphoglyceraldehyde to 1 3 bisphosphoglycerate.
6 1 3 bisphosphoglycerate is converted to 3 phosphoglycerate with the formation of ATP this reaction is catalyzed by an enzyme phosphoglycerate kinase.
7 3 phosphoglycerate is subsequently isomerised to form to phosphoglycerate catalyzed by an enzyme phosphoglyceromutase.
8 in the presence of an enzyme enolase with the loss of a water molecule 2 phosphoglycerate is converted to phospho phenol pyruvate this conversion is also called as dehydration reaction in glycolysis.
9 high energy phosphate group of phospho phenol pyruvate is transfer to a molecule of ATP by the action of enzyme pyruvate kinase in the presence of MG 2 + and K plus this produces 2 molecule of pyruvic acid and a molecule of ATP the pyruvic acids produced is the key product of glycolysis.

Answer 2

NCERT based Answer for Class 11 Biology Students

Glycolysis (glycos- sugar; lysis- splitting):  

 The partial oxidation of glucose to pyruvic acid without help of oxygen is called glycolysis.

 The scheme of glycolysis was given by Embden, Meyerhoff and Parnas; therefore it is referred to as EMP pathway.

 In anaerobic organisms, it is the only process in respiration.

 Glycolysis occurs in cytoplasm of cell.

 In plants, glucose is derived from sucrose. Sucrose is converted into glucose and fructose by the enzyme invertase.

 Glycolysis occurs in 10 steps, the first five steps constitute preparatory phase. In preparatory phase, ATP is utilized at two steps: first in the conversion of glucose to glucose 6-phosphate and second in the conversion of fructose 6-phosphate to fructose 1, 6- bisphosphate.

 The last five steps constitute pay off phase. In this phase, glyceraldehyde 3- phosphate oxidized to 1, 3 bisphosphoglyceric acid along with reduction of one molecule of NAD+ to NADH. ATP is formed at two steps: first in conversion of 1, 3 bisphosphoglyceric acid to 3- phosphoglyceric acid and second in conversion of 2- phosphoenolpyruvate to pyruvic acid.

 Pyruvic acid is the key product of glycolysis.

Note: Three types of chemical transformation occur in glycolysis:

• Phosphorylation: Transfer of phosphate group from ATP and intermediate molecule.

• Degradation of carbon skeleton: Conversion of 6- C glucose to 3- C pyruvic acid.

• Transfer of hydride ion (H+) with its electron to NAD+ forming NADH.

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