Question

During EMP pathway, ATP is produced through
A. Oxidative phosphorylation
B. Cyclic phosphorylation
C. Substrate phosphorylation
D. None of the above

Answer 1

Hint: EMP pathway is also called Glycolysis. It is common in Aerobic as well as anaerobic respiration in plants. It occurs in cytoplasm during aerobic respiration. During this process glucose undergoes partial oxidation and forms two molecules of pyruvic acid.

Complete answer:
Preparatory phase:

1.Phosphorylation of Glucose: Glucose is phosphorylated to form glucose-6-phosphate by one molecule of ATP in the presence of enzyme hexokinase (Meyerhof, 1927) or glucokinase (in liver) and Magnesium ions.

2.Synthesis of Fructose-6-phosphate : Glucose-6 phosphate is converted to its isomer that is fructose-6-phosphate with the help of enzyme phosphohexose isomerase.

3.Formation of Fructose-1.6-biphosphate: Fructose 6-phosphate is further phosphorylated by means of ATP in presence of enzyme phosphofructokinase and magnesium ions. The product is fructose 1:6 bisphosphate.

4.Splitting : Fructose-1 6 bisphosphate splits up enzymatically to form one molecule cach of 3-carbon compounds, glyceraldehyde 3-phosphate (GAP or 3-phosphoglyceraldehyde - PGAL) and dihydroxyacetone 3-phosphate (DiHAP)

5.Isomerisation of DIHAP : Dihydroxyacetone 3-phosphate is isomerised to glyceraldehyde-3-phosphate with the help of enzyme triose phosphate isomerase.

Energy Conserving Phase:

6.Oxidation and Phosphorylation: In the presence of enzyme glyceraldehyde-3-phosphate dehydrogenase, the glyceraldehyde-3-phosphate is oxidised through removal of hydrogen and addition of phosphate from inorganic source to form 1 : 3 diphosphoglycerate NAD is hydrogen acceptor. It produces NADH
7.Substrate Level Phosphorylation (Formation of ATP): One of the two phosphates of bisphosphoglycerate is linked by high energy bonds. It can form 3-phosphoglycerate and synthesise ATP .The enzyme acts as phosphoglycerate kinase. This type of direct synthesis of ATP from metabolism is called substrate level phosphorylation

8. Isomerization: 3-phosphoglycerate is changed to its isomer 2-phosphoglycerate by enzyme phosphoglyceromutase.

9.Dehydration : Through the agency of enzyme enolase, 2-phosphoglycerate is converted to phosphoenolpyruvate (PEP). A water molecule is removed in the process.

10. Formation of Pyruvate : The phosphate radical picks up energy during formation of phosphoenolpyruvate. It helps in the ATP production by substrate level phosphorylation. The enzyme is pyruvate kinase.

Hence, the correct answer is option (C)

Note: Types of Respiration.It is mainly of two types :(i) Aerobic (ii) Anaerobic
(i) Aerobic respiration : when respiratory substrates are broken down with the help of atmospheric Oxygen is called aerobic respiration
(ii) Anaerobic respiration : The incomplete breakdown of respiratory substrates in absence of oxygen is known as anaerobic respiration. Anaerobic respiration was first studied by Kostychev (1902).