Bachelor’s Degree Programme (BSCG) – Plant Physiology and Metabolism Assig. Answer | BBYCT–137(Q-5)
5. a) Describe the process of glycolysis with the help of a labelled diagram.
b) Graphically illustrate the effect of substrate concentration on the rate of an enzyme-mediated reaction.
a) The Process of Glycolysis:-
1. Glucose is phosphorylated (addition of phosphate group) to glucose 6-phosphate by enzyme hexokinase. This is an irreversible reaction, dependent on ATP and Mg ion.
2. Glucose 6-phosphate undergoes isomerization to give fructose 6-phosphate in the presence of the enzyme phosphohexose isomerase and Mg ion.
3. Fructose 6-phosphate is phosphorylated to fructose 1,6-bisphosphate by enzyme phosphofructokinase (PFK). This is an irreversible step in glycolysis.
4. The six-carbon fructose 1,6- bisphosphate is split (hence the name glycolysis) into 2 three-carbon compounds, glyceraldehyde 3-phosphate, and dihydroxyacetone phosphate by the enzyme aldolase.
5. The enzyme phosphotriose isomerase catalyzes the interconversion of glyceraldehyde 3-phosphate and dihydroxyacetone phosphate. This interconversion is reversible. So, Two molecules of glyceraldehyde 3-phosphate are obtained from one molecule of glucose.
6. Enzyme glyceraldehyde 3-phosphate dehydrogenase converts glyceraldehyde 3-phosphate to 1,3-bisphosphoglycerate. This step is important as it is involved in the formation of NADH + H+.
7. The enzyme phosphoglycerate kinase acts on a 1,3-bisphosphoglycerate molecule resulting in the formation of 3-phosphoglycerate and synthesis of ATP.
8. 3-Phosphoglycerate molecule is converted to a 2-phosphoglycerate molecule by the enzyme phosphoglycerate mutase. This is an isomerization reaction.
9. The high energy compound phosphoenolpyruvate is generated from 2-phosphoglycerate by the enzyme enolase.
10. The enzyme pyruvate kinase catalyzes the transfer of high energy phosphate from phosphoenolpyruvate to ADP, leading to the formation of ATP.
b) The curve shows the effect of substrate concentration on the rate of an enzyme-catalyzed reaction. It shows that increasing substrate concentration increases the rate of reaction until a point comes when all the active sites of enzyme molecules are saturated with substrates and increasing the substrate concentration has no effect on the rate of reaction. The presence of an enzyme inhibitor would reduce the reaction rate. The formation of the enzyme complex is shown in the graph of the free energy level of the reaction mixture to the progress of the reaction. The graph is showing the relation between the rate of reaction and substrate concentration, not the pH of the reaction mixture.