Glycolysis and MCQs for GPAT, NEET, CSIR NET, UPSC

Glycolysis and MCQs for GPAT, NEET, CSIR NET, UPSC

Glycolysis is also known as Embden Meyerhof pathway. In glycolysis, a molecule of glucose is degraded to form two molecules of pyruvate in the presence of oxygen with the help of a series of enzymes. during glycolysis, some of the free energy released from glucose is conserved in the form of ATP and NADH. 

Silent Features of Glycolysis

  1. Glycolysis takes place in all the cells of the body. The enzymes of glycolysis are mostly present in the cytosol of the cell
  2. Glycolysis occur both in presence and in absence of oxygen. The end product of aerobic glycolysis is pyruvate which is then oxidized to form CO2 and H2O. While the end product of anerobic glycolysis is lactate.
  3. It is the major pathway for the synthesis of ATP in the tissues lacking mitochondria. Eg: RBCs
  4. Glycolysis is essential for the brain because brain is dependent on glycolysis for the glucose supply.
  5. Reversal of the glycolysis with some other arrangements  results in the synthesis of glucose (Gluconeogenesis).

Reactions of Glycolysis

The breakdown of glucose to form two molecules of pyruvate is done with the help of 10 enzymes; which is divided in two phases.

  • 1st Phase:- This is energy requiring phase or the preparative phase. First five reactions of the pathway falls in this phase; where the phosphorylated form of glucose and fructose are synthesized at the cost of 2 mole of ATP per glucose molecule.
  • 2nd Phase:- This is known as energy generating phase. The rest of the reaction of the pathway comes under this phase; where nine ATP molecules are formed per glucose molecule.

Regulation of glycolysis

Glycolysis pathway has dual functions:

  1. It degrades glucose to generate ATP molecules
  2. It forms the building blocks for the synthetic reactions like formation of fatty acids.

Glycolysis is regulated by two factors:

1. Enzymatic control: there are several enzymes whose concentration can either inhibit or stimulate the glycolysis process; these are:

                   a. Hexokinase- It is an allosteric enzyme which catalyses the first step of glycolysis. It is inhibited the its product (glucose-6-phosphate). High concentration of glucose-6-phosphate sgnals the cell for no longer requirement of glucose for energy or other functions. This is known as feedback inhibition

                   b.  Phosphofructose kinase-1:-

  • High level of ATP allosterically inhibits the enzyme by inhibiting its affinity for its substrate (fructose-6-phosphate).
  • AMP works with opposite effect of that of ATP; as it increases the enzymatic activity during low energy level.

This is known as allosteric inhibition.

                    c. Pyruvate kinase:-

  • During high energy levels, The ATP allosterically inhibits the enzyme.
  • Alanine (synthesized from pyruvate  in muscles) also inhibit the enzyme.When glycolysis increases, the rate of fructose-1,6 bisphosphate activates the pyruvate kinase. This is known as feedforward stimulation.

2. Hormonal control:-

  • High concentration of Insulin activates the glycolysis
  • High concentration of Glucogen depresses the glycolysis

Significance of glycolysis

  1. It is the basic route for the glucose metabolism
  2. It also provide pathway for the metabolism of fructose and galactose
  3. It has the ability to generate ATP molecules in the absence of oxygen
  4. It generates building blocks for the biosynthetic pathway.
  5. In RBCs, it supplies 2,3-bisphosphoglycerate which is required by Hb to perform its functions

Bio-ENERGETICS of glycolysis

During the aerobic glycolysis of glucose into 2 pyruvate molecules generate:

  • Two molecules of NADH and
  • Four molecules of ATP at the substrate level.

Two molecules of ATP per mole of glucose is consumed for the reactions of hexokinase and phosphofructokinase.

Multiple choice questions (MCQs)

1. what is glycolysis?
A. Utilization of glucose

B. synthesis of glucose

C. synthesis of glycogen

D. breakdown of glycogen

2. Where does glycolysis occur?
A. Cytosol

B. Mitochondria matrix

C. Nucleus

D. Ribosomes

3. Which of the following is the first enzyme of glycolysis?
A. Pyruvate dehydrogenase

B. Phosphofructokinase

C. Hexokinase

D. None of the above

4. which enzyme converts pyruvate to lactate?
A. Pyruvate kinase

B. Pyruvate dehydrogenase

C. Pyruvate carboxylase

D. Enolase

5. which hormone stimulates glycolysis?
A. Insulin

B. Glucagon

C. Growth hormone

D. All of the above

6. Which hormone inhibits glycolysis?
A. Insulin

B. Glucagon

C. Growth hormone

D. All of the above

7. Glycolysis is also known as?

A. Kreb’s cycle

B. Respiratory cycle

C. Embden Meyerhof pathway

D. HMP-shunt

8. Which process shares the same pathway as glycolysis but in opposite direction?
A. Glycogenesis

B. Gluconeogenesis

C. Glycogenolysis

D. HMP-shunt

9. Which of the following statement is NOT true?
A. It occurs in cytosol of the cell
B. It also helps in fructose metabolism
C. Glycolysis generates ATP
D. Glycolysis generates CO2

10. Where do glycolysis leads to lactate production?

A. Liver

B. erythrocytes

C. Cornea

D. medulla 

11. Match the following enzymes with its substrates-
a. Hexokinase 1. Fructose-1,6 bisphosphate
b. Pyruvate kinase 2. 2-phosphoglycerate
C. Enolase 3. Phospho-enol pyruvate
d. Aldolase 4. glucose

12. Which enzyme is inhibited by iodoacetate and arsenate?

A. Hexokinase

B. Glucokinase

C. Glyceraldehyde-3-phosphate dehydrogenase

 D. Both A and B

13. Which of the following enzymes participate in 1st phase of glycolysis?
A. Hexokinase

B. Phospho-glucose isomerase

C. Aldolase

D. All of the above

14. Hexokinase is —– dependent enzyme. Fill in the blank

A. Zinc

B. Magnesium

C. sodium dependent

D. Iron

15. Which of the following enzyme catalyzes the reversible reaction of glycolysis?

A. Glucokinase

B. Phosphofructokinase

C. Pyruvate kinase 

D. None of the above

ANSWERS:-

1. Utilization of glucose

2. Cytosol

3. Hexokinase

4. Pyruvate dehydrogenase

5. Insulin

6. Glucagon

7. Embden Meyerhof pathway

8. Gluconeogenesis

9. Glycolysis generates CO2

10. 2

11. a – 4 b – 3 c – 2 d – 1

12. Glyceraldehyde-3-phosphate dehydrogenase

13. All of the above

14. Magnesium

15. None of the above

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REFERENCE:- 1. Pankaja Naik- Biochemistry; 4th edition; page no:- 160-166.

2. U Satyanarayana, U chakrapani- Biochemistry; 4th edition; page no- 245-248. 

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