Glycolysis Cycle

glycolysis cycle

Q. 1

Glycolysis occurs in

 A

Cytosol

 B

Mitochondria

 C

Nucleus

 D

Lysosome

Q. 1

Glycolysis occurs in

 A

Cytosol

 B

Mitochondria

 C

Nucleus

 D

Lysosome

Ans. A

Explanation:

Cytosol [Ref. Harper 26/e, p 136]

Reactions/Pathways                                Site                                         

Glycolysis

Kreb’s cycle

Electron transport chain

1-11V1P shunt

Fatty acid synthesis

Fatty acid oxidation

Oxidation of very long chain fatty acids

Glycogenesis

Glycogenolysis

Gluconeogenesis

Urea cycle

Cytosol

Mitochondria

Mitochondria

Cytosol

Cytosol

Mitochondria

Peroxisomes

Cytosol

Cytosol

Both cytosol & mitochindria

Both cytosol & mitochondria



Q. 2 Net ATP’s formed in glycolysis are:
 A 5
 B 8
 C 10
 D 15
Q. 2 Net ATP’s formed in glycolysis are:
 A 5
 B 8
 C 10
 D 15
Ans. B

Explanation:

8


Q. 3

What is the net amount of ATP’s formed in aerobic glycolysis?

 A

5

 B

8

 C

10

 D

15

Q. 3

What is the net amount of ATP’s formed in aerobic glycolysis?

 A

5

 B

8

 C

10

 D

15

Ans. B

Explanation:

During aerobic glycolysis the number of net ATPs formed are 8.
Steps involved in the formation of ATP during glycolysis are:
  • Conversion of 2 molecules of glyceraldehyde 3 phosphate to 1,3 bisphoglycerate release 2 molecules of NADH which yield 6 ATP.
  • Conversion of 2 molecules of 1,3 BPG to 3 phosphoglycerate yield 2 ATP.
  • Conversion of 2 molecules of phosphoenol pyruvate to pyruvate yield 2 ATP.
Steps involved in the consumption of ATP during glycolysis are:
  • Conversion of glucose to glucose 6 phosphate 
  • Conversion of fructose 6 phosphate to fructose 6 bis phosphate
  • Total ATP formed during glycolysis  : 10
  • ATP utilised  during glycolysis          :   2
  • Net ATP formed during glycolysis    :   8
Net ATP produced during anaerobic glycolysis is only 2.
 
Ref: Medical Biochemistry By N. Mallikarjuna Rao page 160.

Quiz In Between


Q. 4

Net ATP’s formed in glycolysis are:

 A

5

 B

8

 C

10

 D

15

Q. 4

Net ATP’s formed in glycolysis are:

 A

5

 B

8

 C

10

 D

15

Ans. B

Explanation:

Aerobic glycolysis is a process of splitting of glucose into two molecules of pyruvate with the synthesis of ATP. Net ATP formed in aerobic glycolysis is 8.
 
Glycolysis: is the process by which glucose or other hexoses are converted into the three-carbon compound pyruvate. All the reactions takes place in cytoplasm.
  • Aerobic glycolysis: is a process of splitting of glucose into two molecules of pyruvate with the synthesis of ATP.
  • Anaerobic Glycolysis: glycolysis is the only process in which ATP is generated anaerobically. This is of importance because RBC which does not have a mitochondria is wholly dependant on the anaerobic energy production. The byproduct of anaerobic glycolysis is lactate.
Glycolytic pathway: occurs in cytoplasm consists of 10 steps. The first five steps result in one molecule of glucose is converted to 2 glyceraldehyde-3-phosphate molecules at the expense of two molecules of ATPs. The second five steps results in the production of 2 ATP molecules per one molecule of glucose.
  • Rate limiting step: Phosphofructokinase the commited step of glycolysis.
  • Irreversibles steps:
               Hexokinase or glucokinase
               Phosphofructokinase
               Pyruvate kinase
 
No of ATP generated is:
Aerobic glycolysis 8
Anaerobic glycolysis 2
 

Enzyme

Reducing Equivalents

ATP

Glucokinase

 

– 1 ATP

Phosphofructokinase

 

– 1 ATP

Glyceraldehyde 3 phosphate dehydrogenase

2 NADH

 6 ATP

Phosphoglycerate kinase

 

 2 ATP

Pyruvate kinase

 

 2 ATP

NET ATP

 

 8 ATP

 
Ref: Essentials of Medical Biochemistry: With Clinical Cases, By Chung-Eun Ha, N. V. Bhagavan, Page 115

Q. 5

What is the net ATP’s formed in glycolysis?

 A

5

 B

7

 C

10

 D

15

Q. 5

What is the net ATP’s formed in glycolysis?

 A

5

 B

7

 C

10

 D

15

Ans. B

Explanation:

ATP formation in glycolysis:

Reaction Catalyzed by

Method of ATP Formation

ATP per mol of Glucose

Glyceraldehyde 3-phosphate dehydrogenase

Respiratory chain oxidation of 2 NADH

5

Phosphoglycerate kinase

Substrate-level phosphorylation

2

Pyruvate kinase

Substrate-level phosphorylation

2

   

Total 9

 

Consumption of ATP for reactions of hexokinase and phosphofructokinase

-2

   

Net 7

Ref: Bender D.A., Mayes P.A. (2011). Chapter 18. Glycolysis & the Oxidation of Pyruvate. In D.A. Bender, K.M. Botham, P.A. Weil, P.J. Kennelly, R.K. Murray, V.W. Rodwell (Eds), Harper’s Illustrated Biochemistry, 29e.


Q. 6

Which of the following statements about anaerobic glycolysis is INCORRECT?

 A

Anaerobic glycolysis yields two molecules of lactate and two molecules of ATP

 B

There are two oxidation-reduction steps in the anaerobic glycolysis.

 C

The lactated formed in the muscles in the condition of an oxygen deficit can be recycled through the Cori cycle.

 D

The extraction of energy from the molecule of glucose in the anaerobic glycolysis happens due to the net change in the oxidation state of carbon

Q. 6

Which of the following statements about anaerobic glycolysis is INCORRECT?

 A

Anaerobic glycolysis yields two molecules of lactate and two molecules of ATP

 B

There are two oxidation-reduction steps in the anaerobic glycolysis.

 C

The lactated formed in the muscles in the condition of an oxygen deficit can be recycled through the Cori cycle.

 D

The extraction of energy from the molecule of glucose in the anaerobic glycolysis happens due to the net change in the oxidation state of carbon

Ans. D

Explanation:

Although there are two oxidation-reduction steps is the anaerobic glycolysis, and the energy for the synthesis of two ATP molecules is released, there is no net change in the oxidation state of carbon. The first oxidative reaction is catalyzed by glyceraldehyde-3-phosphate dehydrogenase to yield NADH. Later, NADH is spent for the reduction of pyruvate to the lactate which is catalyzed by lactate dehydrogenase. The ratio between C, H, and O atoms is the same for both glucose, C6H12O6 and lactic acid C3H6O3.

 
Ref: Bender D.A., Mayes P.A. (2011). Chapter 18. Glycolysis & the Oxidation of Pyruvate. In D.A. Bender, K.M. Botham, P.A. Weil, P.J. Kennelly, R.K. Murray, V.W. Rodwell (Eds), Harper’s Illustrated Biochemistry, 29e.

Quiz In Between


Q. 7

Which of the following occurs during glycolysis?

 A

Glucose is reduced to pyruvate in the cytosol of all cells.

 B

The rate-limiting step is the formation of fructose-6-phosphate.

 C

Glucose is phosphorylated by aldolase.

 D

Pyruvate, NADH, and ATP are produced.

Q. 7

Which of the following occurs during glycolysis?

 A

Glucose is reduced to pyruvate in the cytosol of all cells.

 B

The rate-limiting step is the formation of fructose-6-phosphate.

 C

Glucose is phosphorylated by aldolase.

 D

Pyruvate, NADH, and ATP are produced.

Ans. D

Explanation:

In virtually all cells of the body, glycolysis is the primary pathway for carbohydrate catabolism.
During glycolysis, glucose undergoes oxidation to form pyruvate, NADH, and ATP. The initial reaction of glycolysis involves phosphorylation of glucose to glucose-6-phosphate via the enzyme hexokinase (glucokinase in liver).
The first committed step involves the phosphorylation of fructose-6-phosphate to fructose-1,6-diphosphate by phosphofructokinase (PFK). The reactions catalyzed by hexokinase and PFK are two of three irreversible reactions occurring in glycolysis.
The other irreversible reaction involves pyruvate kinase. In terms of the energetics of the reactants and products, it is important to remember that every intermediate in this pathway between glucose and pyruvate contains phosphate.
 
Ref: Bender D.A., Mayes P.A. (2011). Chapter 18. Glycolysis & the Oxidation of Pyruvate. In D.A. Bender, K.M. Botham, P.A. Weil, P.J. Kennelly, R.K. Murray, V.W. Rodwell (Eds), Harper’s Illustrated Biochemistry, 29e.

Q. 8

Within the RBC, hypoxia stimulates glycolysis by which of the following regulating pathways?

 A

Hypoxia stimulates pyruvate dehydrogenase by increased 2,3 DPG

 B

Hypoxia inhibits hexokinase

 C

Hypoxia stimulates release of all glycolytic enzymes from band 3 on RBC membrane

 D

Activation of the regulatory enzymes by high PH

Q. 8

Within the RBC, hypoxia stimulates glycolysis by which of the following regulating pathways?

 A

Hypoxia stimulates pyruvate dehydrogenase by increased 2,3 DPG

 B

Hypoxia inhibits hexokinase

 C

Hypoxia stimulates release of all glycolytic enzymes from band 3 on RBC membrane

 D

Activation of the regulatory enzymes by high PH

Ans. C

Explanation:

During Hypoxia, the glycolytic enzymes that bind in the same region of band 3 of Hb are released from the membrane resulting in an increased rate of glycolysis. Increased glycolysis increases ATP production and the hypoxic release of ATP.
 
Ref: Oxygen Transport to Tissue, Xxxiii, edited by Martin Wolf, David K Harrison, 2012, Page 188.

Q. 9

Phosphofructokinase-1 occupies a key position in regulating glycolysis and is also subjected to feedback control. Which among the following is the allosteric activators of phosphofructokinase-1?

 A

Fructose 2, 3 bisphosphate

 B

Fructose 2, 6 bisphosphate

 C

Glucokinase

 D

PEP

Q. 9

Phosphofructokinase-1 occupies a key position in regulating glycolysis and is also subjected to feedback control. Which among the following is the allosteric activators of phosphofructokinase-1?

 A

Fructose 2, 3 bisphosphate

 B

Fructose 2, 6 bisphosphate

 C

Glucokinase

 D

PEP

Ans. B

Explanation:

The most potent positive allosteric activator of phosphofructokinase-1 and inhibitor of fructose 1,6-bisphosphatase in the liver is fructose 2,6-bisphosphate.

  • It relieves inhibition of phosphofructokinase-1 by ATP and increases the affinity for fructose 6-phosphate. 
  • It inhibits fructose 1,6-bisphosphatase by increasing the Km for fructose 1,6-bisphosphate. 
  • Its concentration is under both substrate (allosteric) and hormonal control (covalent modification).
Phosphofructokinase-1 is inhibited by citrate and by normal intracellular concentrations of ATP and is activated by 5′ AMP.
 
Ref: Bender D.A., Mayes P.A. (2011). Chapter 20. Gluconeogenesis & the Control of Blood Glucose. In D.A. Bender, K.M. Botham, P.A. Weil, P.J. Kennelly, R.K. Murray, V.W. Rodwell (Eds), Harper’s Illustrated Biochemistry, 29e.

Quiz In Between


Q. 10

Glycolysis is the metabolic pathway that involves 10 enzyme mediated steps. It occur in which of the following cell organelle?

 A

Cytosol

 B

Mitochondria

 C

Nucleus

 D

Lysosome

Q. 10

Glycolysis is the metabolic pathway that involves 10 enzyme mediated steps. It occur in which of the following cell organelle?

 A

Cytosol

 B

Mitochondria

 C

Nucleus

 D

Lysosome

Ans. A

Explanation:

Glycolysis, the major pathway for glucose metabolism, occurs in the cytosol of all cells. Glycolysis is both the principal route for glucose metabolism and also the main pathway for the metabolism of fructose, galactose, and other dietary carbohydrates. 

Ref: Bender D.A., Mayes P.A. (2011). Chapter 18. Glycolysis & the Oxidation of Pyruvate. In D.A. Bender, K.M. Botham, P.A. Weil, P.J. Kennelly, R.K. Murray, V.W. Rodwell (Eds), Harper’s Illustrated Biochemistry, 29e.

 


Q. 11

Enzymes of glycolysis are found in:

 A

Cytosol

 B

Cell membrane

 C

Mitochondria

 D

Ribososmes

Q. 11

Enzymes of glycolysis are found in:

 A

Cytosol

 B

Cell membrane

 C

Mitochondria

 D

Ribososmes

Ans. A

Explanation:

All of the enzymes of glycolysis are found in the cytosol.
           
Ref: Harper 28th edition, chapter 18.

Q. 12

Common to both glycolysis and pentose phosphate pathway is:

 A

Glucose 6 phosphate

 B

NAD

 C

ATP

 D

All of the above

Q. 12

Common to both glycolysis and pentose phosphate pathway is:

 A

Glucose 6 phosphate

 B

NAD

 C

ATP

 D

All of the above

Ans. A

Explanation:

Although glucose 6-phosphate is common to both pathways, the pentose phosphate pathway is markedly different from glycolysis. Oxidation utilizes NADP rather than NAD, and CO2, which is not produced in glycolysis, is a characteristic product. No ATP is generated in the pentose phosphate pathway, whereas it is a major product of glycolysis
Ref: Harper 28th edition, chapter 21.

Quiz In Between


Q. 13

Which of the following is an energy-requiring step of glycolysis?

 A

Pyruvate carboxylase

 B

Phosphoenolpyruvate carboxykinase

 C

Phosphoglycerate kinase

 D

Hexokinase

Q. 13

Which of the following is an energy-requiring step of glycolysis?

 A

Pyruvate carboxylase

 B

Phosphoenolpyruvate carboxykinase

 C

Phosphoglycerate kinase

 D

Hexokinase

Ans. D

Explanation:

Hexokinase catalyzes the conversion of glucose to glucose-6-phosphate in the energy-requiring first step of glycolysis. ATP is also required in the conversion of fructose-6-phosphate to fructose 1,6-bisphosphate by PFK. ATP is generated in the conversion of 1,3-bisphosphoglycerate to 3-phosphoglycerate by phosphoglycerate kinase and in the conversion of phosphoenolpyruvate to pyruvate by PK. Both phosphoenolpyruvate carboxykinase and pyruvate carboxylase are energy-requiring reactions except that these occur in the gluconeogenesis pathway.

Ref: Bender D.A., Mayes P.A. (2011). Chapter 18. Glycolysis & the Oxidation of Pyruvate. In D.A. Bender, K.M. Botham, P.A. Weil, P.J. Kennelly, R.K. Murray, V.W. Rodwell (Eds), Harper’s Illustrated Biochemistry, 29e. 

 


Q. 14

In glycolysis, the following forms as the byproduct:

 A

Pyruvate

 B

H2O

 C

H+

 D

All of the above

Q. 14

In glycolysis, the following forms as the byproduct:

 A

Pyruvate

 B

H2O

 C

H+

 D

All of the above

Ans. D

Explanation:

Glycolysis is the metabolic pathway that breaks down (catabolism) hexose (six-carbon) monosaccharides such as glucose, fructose, and galactose into two molecules of pyruvate, two molecules of ATP, two molecules of NADH, two water (H2O) molecules, and two hydrogen ions (H+).
 
Ref: Janson L.W., Tischler M.E. (2012). Chapter 6. Carbohydrate Metabolism. In L.W. Janson, M.E. Tischler (Eds), The Big Picture: Medical Biochemistry.

Q. 15

Enzyme catalyzing reversible step in glycolysis is/are:

 A

Glyceraldehyde-3-phosphate-dehydrogenase

 B

Enolase

 C

Phospho-glyceromutase

 D

All Correct

Q. 15

Enzyme catalyzing reversible step in glycolysis is/are:

 A

Glyceraldehyde-3-phosphate-dehydrogenase

 B

Enolase

 C

Phospho-glyceromutase

 D

All Correct

Ans. D

Explanation:

A, B, C i.e. Enolase, Phospho-glyceromutase, Glyceraldehyde-3-phosphate-dehydrogenase

Quiz In Between


Q. 16

About glycolysis true is:

 A

Occurs in mitochondria

 B

Complete breakdown of glucose

 C

Conversion of glucose to 3C units

 D

3 ATP’s are used in anaerobic pathway

Q. 16

About glycolysis true is:

 A

Occurs in mitochondria

 B

Complete breakdown of glucose

 C

Conversion of glucose to 3C units

 D

3 ATP’s are used in anaerobic pathway

Ans. C

Explanation:

  1. C i.e. Conversion of glucose to 3 C units
  • Enzymes of glycolysis – a process which converts 6 carbon glucose to 3 carbon unit pyruvate & lactateQ – are present in cytoplasm. Whereas complete oxidation of glucose (to CO) & H20) requires mitochondrial enzymes (of TCA cycle).
  • Out of total 9 enzymes used in glycolysis

–   3 enzymes – hexokinase, phosphofructokinase (PFK-1) and Pyruvate kinase are used in irreversible steps.

 

–   6 enzymes – phosphohexose isomerase, aldolase, glyceraldehydes 3 phosphate dehydrogenase, 1, 3- biphospho glycerate kinase, phosphoglyceromutase and enolase are used in reversible stepsQ.

–   2 enzymes used in energy utilizing steps are – hexokinase (using 1 ATP) and phosphofructokinase PFK-1 (using 1 ATP). This energy consumption is for 1 molecule of glucose.

–  3 enzymes used in energy producing steps are – glyceraldehydes 3phosphate dehydrogenase (producing 2 NADH = 5 ATP), 1, 3 – biphospho glycerate kinase (producing 2 ATP), and pyruvate kinase (producing 2 ATP). This energy production is for 1 molecule of glucose or 2 molecules of glyceraldehyde 3-P.

 


Q. 17

Compound that joints glycolysis with glycogenesis & glycogenolysis :

 A

Glucose 1, 6 bi phosphate

 B

Glucose 1 PO4

 C

Glucose 6 PO4

 D

Fructose 1, 6 bi phosphate

Q. 17

Compound that joints glycolysis with glycogenesis & glycogenolysis :

 A

Glucose 1, 6 bi phosphate

 B

Glucose 1 PO4

 C

Glucose 6 PO4

 D

Fructose 1, 6 bi phosphate

Ans. C

Explanation:

C i.e. Glucose 6 PO4

Glucose 6 phosphate is an important compound that joins several metabolic pathways viz. glycolysis, glycogenolysis, glycogenesis, gluconeogenesis and pentose phosphate pathwayQ


Q. 18

Irreversible step (s) in glycolysis is/are:

 A

Hexokinase

 B

Phosphofructokinase

 C

Pyruvate kinase

 D

All of the above

Q. 18

Irreversible step (s) in glycolysis is/are:

 A

Hexokinase

 B

Phosphofructokinase

 C

Pyruvate kinase

 D

All of the above

Ans. D

Explanation:

All of the above

Quiz In Between


Q. 19

In glycolysis, the first commited step is catalysed by :

 A

2 ,3 DPG

 B

Glucokinase

 C

Hexokinase

 D

Phosphofructokinase.

Q. 19

In glycolysis, the first commited step is catalysed by :

 A

2 ,3 DPG

 B

Glucokinase

 C

Hexokinase

 D

Phosphofructokinase.

Ans. D

Explanation:

D i.e. Phosphofructokinase


Q. 20

The rate-limiting enzyme in Glycolysis is :

 A

Phosphofructokinase

 B

Glucose-6-dehydrogenase

 C

Glucokinase

 D

Pyruvate kinase

Q. 20

The rate-limiting enzyme in Glycolysis is :

 A

Phosphofructokinase

 B

Glucose-6-dehydrogenase

 C

Glucokinase

 D

Pyruvate kinase

Ans. A

Explanation:

Ans:A i.e. Phosphofructokinase.

Rate-Limiting Enzymes 

  • Rate-limiting enzyme of Glycolysis :Phosphofructokinase-1 (PFK-1)
  • Rate-limiting enzyme of Gluconeogenesis :Fructose-1,6,biphosphatase
  • Rate-limiting enzyme of TCA cycle :Isocitrate dehydrogenase
  • Rate-limiting enzyme of Glycogen Synthesis :Glycogen synthase
  • Rate-limiting enzyme of Glycogenolysis :Glycogen phophorylase (phophorylase breaks phosphate bond, which means activated glycogen releases a lot of energy)
  • Rate-limiting enzyme of HMP Shunt :Glucose-6-Phosphate dehydrogenase (bad to lose this in RBCs)
  • Rate-limiting enzyme of de novo pyrimidine synthesis :Carbamoyl phosphate synthase II (CPS I is involved in urea cycle)
  • Rate-limiting enzyme of de novo purine synthesis :Glutamine-PRPP amidotransferase
  • Rate-limiting enzyme of Urea cycle :Carbamoyl phosphate synthetase I (CPS II is involved in pyrimidine synthesis)
  • Rate-limiting enzyme of fatty acid synthesis :Acetyl-CoA carboxylase (ACC)
  • Rate-limiting enzyme of fatty acid oxidation :Carnitine acyltransferase I
  • Rate-limiting enzyme of Ketogenesis :HMG-CoA synthase
  • Rate-limiting enzyme of Cholesterol synthesis :HMG-CoA reductase

Q. 21

Enzyme to both common in gluconegenesis and glycolysis pathway is :

 A

Phosphofructokinase

 B

Fructose 2,6-biphosphatase

 C

Hexokinase

 D

Glucose 6 phosphatase

Q. 21

Enzyme to both common in gluconegenesis and glycolysis pathway is :

 A

Phosphofructokinase

 B

Fructose 2,6-biphosphatase

 C

Hexokinase

 D

Glucose 6 phosphatase

Ans. A

Explanation:

A i.e. Phosphofructokinase

Quiz In Between


Q. 22

Glycolysis occurs in

 A

Cytosol

 B

Mitochondria

 C

Nucleus

 D

Lysosome

Q. 22

Glycolysis occurs in

 A

Cytosol

 B

Mitochondria

 C

Nucleus

 D

Lysosome

Ans. A

Explanation:

A i.e. Cytosol


Q. 23

In glycolysis, insulin affects all of the following en­zymes except:       

 A

Phosphofructokinase

 B

Pyruvate kinase

 C

Glucokinase

 D

Hexokinase

Q. 23

In glycolysis, insulin affects all of the following en­zymes except:       

 A

Phosphofructokinase

 B

Pyruvate kinase

 C

Glucokinase

 D

Hexokinase

Ans. D

Explanation:

 

The activation as well as the quantities of certain key enzymes of glycolysis, namely glucokinase (NOT hexokinase), phosphofructokinase and pyruvate kinase are increased by insulin.


Q. 24

Key glycolytic enzymes in glycolysis are all except:

 A

Phosphofructokinase

 B

Hexokinase

 C

Pyruvate kinase

 D

Glucose-1, 6, diphosphatase

Q. 24

Key glycolytic enzymes in glycolysis are all except:

 A

Phosphofructokinase

 B

Hexokinase

 C

Pyruvate kinase

 D

Glucose-1, 6, diphosphatase

Ans. D

Explanation:

 

Glycolysis/Embden-Meyerhof pathway is the sequence of reactions that converts glucose into pyruvate with the concomitant production of a relatively small amount of adenosine triphosphate (ATP)

It is the initial process of most carbohydrate catabolism, and it serves three principal functions:

  • Generation of high-energy molecules (ATP and NADH) as cellular energy sources as part of aerobic respiration and anaerobic respiration.
  • Production of pyruvate for the citric acid cycle as part of aerobic respiration
  • Production of a variety of six- and three-carbon intermediate compounds, which may be removed at various steps in the process for other cellular purposes

In eukaryotes and prokaryotes, glycolysis takes place within the cytosol of the cell.

Quiz In Between


Q. 25

What is the end product of anearobic glycolysis?

 A

Pyruvate

 B

Lactate

 C

Fats

 D

Cholesterol

Q. 25

What is the end product of anearobic glycolysis?

 A

Pyruvate

 B

Lactate

 C

Fats

 D

Cholesterol

Ans. B

Explanation:

Q. 26

Which is not a common enzyme for glycolysis and gluconeogenesis?

 A

Aldolase

 B

Glucose-6-phosphatase

 C

Phosphoglycerate mutase

 D

Phosphoglycerate kinase

Q. 26

Which is not a common enzyme for glycolysis and gluconeogenesis?

 A

Aldolase

 B

Glucose-6-phosphatase

 C

Phosphoglycerate mutase

 D

Phosphoglycerate kinase

Ans. B

Explanation:

 

Seven of the reactions of glycolysis are reversible and are used in the synthesis of glucose by gluconeogenesis.

Thus, seven enzymes are common to both glycolysis and gluconeogenesis :

(i) Phosphohexose isomerase;

(ii) Aldolase;

(iii) Phosphotriose isomerase,

(iv) Glyceraldehyde 3-phosphate dehydrogenase;

(v) Phosphoglycerate kinase;

(vi) Phosphoglycerate mutase;

(vii) Enolase.

Three reactions of glycolysis are irreversible which are circumvented in gluconeogenesis by four reactions. So, enzymes at these steps are different in glycolysis and gluconeogenesis.


Q. 27

Number of ATP produced by RBC when Glycolysis occurs through Rapoport Leubering pathway

 A

1

 B

2

 C

3

 D

4

Q. 27

Number of ATP produced by RBC when Glycolysis occurs through Rapoport Leubering pathway

 A

1

 B

2

 C

3

 D

4

Ans. A

Explanation:

 

Usually 2 ATP molecules are formed in glycolysis by substrate level phosphorylation.

Quiz In Between


Q. 28

Which of the following enzyme does not catalyzes irreversible step in glycolysis ‑

 A

Hexokinase

 B

Phosphoglycerate kinase

 C

Pyruvate kinase

 D

Phosphofructokinase

Q. 28

Which of the following enzyme does not catalyzes irreversible step in glycolysis ‑

 A

Hexokinase

 B

Phosphoglycerate kinase

 C

Pyruvate kinase

 D

Phosphofructokinase

Ans. B

Explanation:

Ans. is ‘b’ i.e., Phosphoglycorate kinase

Glycolysis is regulated at 3 steps which are irreversible.

These reactions are catalyzed by following key enzymes :‑

1) Hexokinase and glucokinase

2) Phosphofructokinase – I

3) Pyruvate kinase.


Q. 29

Number of ATP molecules and NADH formed in each cycle of glycolysis ‑

 A

4 ATP, 2 NADH

 B

2 ATP, 2 NADH

 C

4 ATP, 4 NADH

 D

2 ATP, 4 NADH

Q. 29

Number of ATP molecules and NADH formed in each cycle of glycolysis ‑

 A

4 ATP, 2 NADH

 B

2 ATP, 2 NADH

 C

4 ATP, 4 NADH

 D

2 ATP, 4 NADH

Ans. A

Explanation:

Ans. is ‘a’ i.e., 4 ATP, 2 NADH

Enegetics of glvcolysis

During glycolysis 2 ATP are utilized and 4 ATP are produced at substrate level. 2 reducing equalents NADH’ are produced and reoxidized by electron transport chain, to generata 5 ATP molecules (2.5 ATP per NADH’ molecule). Thus total 9 ATP molecules are produced and 2 are utilized, i.e., There is net gain of 7 ATP molecules in aerobic glycolysis.

In anaerobic conditions, the reoxidation of NADH by electron transport chain is prevented and NADH gets reoxidized by conversion of pyruvate to lactate by lactate dehydrogenase. Thus, in anaerobic glycolysis only 4 ATP are produced at substrate level. Therefore, there is net gain of 2 ATP molecules in anaerobic glycolysis.

Note : – Previous calculations were made assuming that NADH produces 3 ATPs and FADH2 generates 2 ATPs. This will amount to a net generation of 8ATPs per glucose molecule during glycolysis. Recent experiments show that these old values are overestimates and NADH produces 2.5 ATPs and FADH2 produces 1.5 ATPs. Thus, net generation is only 7ATPs during glycolysis.


Q. 30

Number of ATP molecules formed in anaerobic glycolysis ‑

 A

1

 B

2

 C

4

 D

8

Q. 30

Number of ATP molecules formed in anaerobic glycolysis ‑

 A

1

 B

2

 C

4

 D

8

Ans. C

Explanation:

 

Two different questions can be framed :‑

  • Number of ATP molecules produced in anaerobic glycolysis → 4
  • Number of ATP molecules gained in aerobic glycolysis  2

Quiz In Between


Q. 31

Fructose 2-6 bisphosphate (F26BP) regulates glycolysis at the level of ‑

 A

Glucose -6- phosphate

 B

Fructose -6- phosphate

 C

Glyceraldehyde -3- phosphate

 D

Phosphoenol pyruvate

Q. 31

Fructose 2-6 bisphosphate (F26BP) regulates glycolysis at the level of ‑

 A

Glucose -6- phosphate

 B

Fructose -6- phosphate

 C

Glyceraldehyde -3- phosphate

 D

Phosphoenol pyruvate

Ans. B

Explanation:

 

Regulation of glycolysis

  • Glycolysis is regulated at 3 steps which are irreversible. These reactions are catalyzed by following key enzymes : (1) Hexokinase and glucokinase, (2) Phosphofructokinase I, and (3) Pyruvate kinase.

Hexokinase and glucokinase

  • These enzymes catalyze the first step of glycolysis, i.e., Glucose —> Glucose-6-phosphate. Glucokinase is found in liver, Whereas hexokinase is found in all tissues. Kinetic properties of these two are different.
  • Hexokinase has low Km, i.e., high affinity for glucose, low Vmax, and is subjected to feedback inhibition by the reaction product, glucose-6-phosphate. Hexokinase is found in most of the tissue except liver and comes into play when blood glucose is low. It is not affected by feeding or insulin. Hexokinase is not specific for glucose metabolism, it is also involved in metabolism of fructose and galactose.
  • Glucokinase, on the other hand, is specific for glucose. It has high Km (i.e., low affinity for glucose), high Vmax and unlike hexokinase, it is not inhibited by glucose-6-phosphate. As it has low affinity for glucose (high km), it comes into play only when intracellular glucose concentration is high. It is induced by feeding and insulin. Glucagon inhibits glucokinase.
  • Function of hexokinase is to provide glucose-6-phosphate at a constant rate, according the needs of cells, i.e., function of hexokinase is to provide constant glucose utilization by all tissues of body even when blood sugar is low. Function of glucokinase in the liver is to remove glucose from blood after a meal, providing glucose-6­phosphate in excess of requirement for glycolysis so that it can be used for glycogen synthesis and lipogenesis.

Phosphofructokinase I

  • Phosphofructokinase I is the major regulatory enzyme of glycolysis. It catalyzes the 3rd reaction of glycolysis, i.e., fructose-6-P Fructose 1,6 bis-P. This reaction is irreversible and is the “rate -limiting step” for glycolysis. It is also the “commeted step”, meaning that once fructose 1,6 bisphophate is formed it must go for the glycolytic pathway only. So, most important control point for glycolysis is through regulation of phosphofructokinase I.
  • Phosphofructokinase – I is allosterically activated by : Fructose-6-phosphate, fructose 2,6-bisphophate, AMP, ADP, K+ and phosphate. It is allosterically inhibited by : ATP, citrate, Ca+2, Mg+2, and low pH. Phosphofructokinase is an inducible enzyme that increases its synthesis in response to insulin and decreases in response to glucagon.
  • Fructose 2,6-bisphosphate (F-2,6-BP) is the most important allosteric modulator (activator) of phosphofructokinase-I. Fructose 2,6-bisphosphate is synthesized as a side product of glycolysis. A bifunctional enzyme named PFK-2/Fructose 2,6 bisphosphatase is responsible for regulating the level of fructose 2,6 bisphosphate in the liver. Phosphofuctokinase-2 (PFK-2) activity of this bifunctional enzyme is responsible for synthesis of F-2,6-BP from fructose-6-phosphate and fructose 2,6 bisphosphatase activity is responsible for hydrolysis of F-2,6-BP back to fructose-6-phosphate.

Q. 32

Which of the enzyme of glycolysis is used ingluconeogenesis ‑

 A

Glucokinase

 B

PFK

 C

Pyruvate kinase

 D

Phosphotriose isomerase

Q. 32

Which of the enzyme of glycolysis is used ingluconeogenesis ‑

 A

Glucokinase

 B

PFK

 C

Pyruvate kinase

 D

Phosphotriose isomerase

Ans. D

Explanation:

Ans. is ‘d’ i.e., Phosphotriose isomerase 

Enzyme in gluconeogenesis

  • Seven of the reactions of glycolysis are reversible and are used in the synthesis of glucose by gluconeogenesis. Thus, seven enzymes are common to both glycolysis and gluconeogenesis: (i) Phosphohexose isomerase; (ii) Aldolase; (iii) Phosphotriose isomerase; (iv) Glyceraldehyde 3-phosphate dehydrogenase; (v) Phosphoglycerate kinase; (vi) Phosphoglycerate mutase; (vii) Enolase.
  • Three of the reactions of glycolysis are irreversible and must be circumvented by four special reactions which are unique to gluconeogenesis and catalyzed by : (i) Pyruvate carboxylase, (ii) PEP carboxykinase, (iii) Fructose-1, 6- bisphosphatase, (iv) Glucose-6-phosphatase.

Q. 33

Which of the enzyme of glycolysis is a part ofgluconeogenesis ‑

 A

Pyruvate kinase

 B

PFK

 C

Hexokinase

 D

Phosphoglycerate kinase

Q. 33

Which of the enzyme of glycolysis is a part ofgluconeogenesis ‑

 A

Pyruvate kinase

 B

PFK

 C

Hexokinase

 D

Phosphoglycerate kinase

Ans. D

Explanation:

Ans. is ‘d’ i.e., Phosphoglycerate kinase 

  • Seven of the reactions of glycolysis are reversible and are used in the synthesis of glucose by gluconeogenesis. Thus, seven enzymes are common to both glycolysis and gluconeogenesis: (i) Phosphohexose isomerase; (ii) Aldolase; (iii) Phosphotriose isomerase, (iv) Glyceraldehyde 3-phosphate dehydrogenase; (v) Phosphoglycerate kinase; (vi) Phosphoglycerate mutase; (vii) Enolase.
  • Three reactions of glycolysis are irreversible which are circumvented in gluconeogenesis by four reactions. So, enzymes at these steps are different in glycolysis and gluconeogenesis.

Reactions                                       Enzyme in glycolysis        Enzyme in gluconeogenesis

Glucose – Glucose-6-P                    Hexokinase/glucokinase   Glucose-6-phosphatase

Fructose-6-P – Fructose- I ,6-BP     Phosphofructokinase         Fructose-1-6-bisphosphatase

Phosphoenolpyruvate – Pyruvate    Pyruvate kinase                Pyruvate carboxylase PEP carboxykinase

Quiz In Between


Q. 34

True about glycolysis are all except ‑

 A

Provide nutrition to cancer cells

 B

Substrate level phosphorylation at pyruvate kinase

 C

Two carbon end product is formed

 D

NADPH is formed by glyceraldhyde-3-phosphate dehydrogenase

Q. 34

True about glycolysis are all except ‑

 A

Provide nutrition to cancer cells

 B

Substrate level phosphorylation at pyruvate kinase

 C

Two carbon end product is formed

 D

NADPH is formed by glyceraldhyde-3-phosphate dehydrogenase

Ans. C

Explanation:

Ans. is ‘c’ i.e., Two carbon end product is formed 

Important facts about glycolysis

  • An important biochemical significance is the ability of glycolysis to provide ATP in the absence of oxygen (anerobic glycolysis) and allows tissues to survive anoxic episodes.
  • It occurs in cytosol
  • 3 Carbon atoms end product (pyruvate or lactate) is produced.
  • Irreversible steps are catalyzed by : – Glucokinase/Hexokinase, phosphofructohnase-I, and pyruvate kinase. 
  • Reversible steps are catalyzed by : – Phosphohexose isomerase, aldolase, phosphotriose isomerase, glyceraldehyde 3-phosphate dehydrogenase, Phosphoglycerate kinase, Phosphoglycerate mutase, Enolase.
  • Energy (ATP) using steps are catalyzee by : – Hexokinase/glucokinase, phosphofurctokinase.
  • Energy (ATP) production at substrate level are catalyzed by : Phosphoglycerate kinase, Pyruvate kinase. 
  • Reducing equivalent (NADH) production is catalyzed by : Glyceraldehyde 3-phosphate dehydrogenase.
  • Cancer cells derive nutrition from glycolysis as they have lack of 02 supply because of lack of capillary network. Glycolysis (anaerobic glycolysis) is the only metabolic pathway in the body which can provide energy by glucose metabolism in anerobic conditions.

Q. 35

Anaerobic glycolysis occurs in all places except

 A

Muscles

 B

RBCs

 C

Brain

 D

Kidney

Q. 35

Anaerobic glycolysis occurs in all places except

 A

Muscles

 B

RBCs

 C

Brain

 D

Kidney

Ans. C

Explanation:

Ans. is ‘c’ i.e., Brain 

There are two types of glycolysis : –

  1.  Aerobic glycolysis : – It occurs when oxygen is plentiful and the final product is pyruvate, i.e., final step is catalyzed by pyruvate kinase (see the cycle above). Which is later converted to acetyl CoA by oxidative decarboxylation. There is net gain of 7 ATPs. Acetyl CoA enters TCA cycle.
  2. Anaerobic glycolysis : – It occurs in the absence of oxygen. The pyruvate is fermented (reduced) to lactate in single stage. The reoxidation of NADH (formed in the glyceraldehyde-3-phosphate dehydrogenase step) by respiratory chain is prevented as same NADH is utilized at lactate dehydrogenase step. So, there is no net production of NADH. Thus, there is net gain of 2 ATP only. Unlike pyruvate which is converted to acetyl CoA to enter into krebs cycle, lactate cannot be further utilized by further metabolic pathways. Thus, lactate can be regareded as dead end in glycolysis. Anaerobic glycolysis occurs in exercising skeletal muscle, RBCs, lens, some region of retina, renal medulla, testis and leucocytes.

Q. 36

Reducing equivalants produced in glycolysis are transported from cytosol to mitochondria by ‑

 A

Carnitine

 B

Creatine

 C

Malate shuttle

 D

Glutamate shuttle

Q. 36

Reducing equivalants produced in glycolysis are transported from cytosol to mitochondria by ‑

 A

Carnitine

 B

Creatine

 C

Malate shuttle

 D

Glutamate shuttle

Ans. C

Explanation:

Ans. is ‘c’ i.e., Malate shuttle 

  • Most of the NADH and FADH2, entering the mitochondrial electron transport chain arise from citric acid cycle and 13-oxidation of fatty acids, located in the mitochondria itself.
  • However, NADH is also produced in the cytosol during glycolysis.
  • To get oxidized, NADH has to be transported into the mitochondria as respiratory chain (ETC) is located inside the mitochondria.
  • Since, the inner mitochondrial membrane is not permeable to cytoplasmic NADH, there are special shuttle systems which carry reducing equivalents from cytosolic NADH (rather than NADH itself) into the mitochondria by an indirect route.
  • Two such shuttle systems that can lead to transport of reducing equivalent from the cytoplasm into mitochondria are : –
  1. Malate shuttle (malate-aspartate shuttle system).
  2. Glycerophosphate shuttle.

Quiz In Between


Q. 37

Inhibition of glycolysis by increased supply of 02 is called ‑

 A

Crabtree effect

 B

Pasteur effect

 C

Lewis effect

 D

None

Q. 37

Inhibition of glycolysis by increased supply of 02 is called ‑

 A

Crabtree effect

 B

Pasteur effect

 C

Lewis effect

 D

None

Ans. B

Explanation:

Ans. is ‘b’ i.e., Pasteur effect 

Pasteur effect

  • It has been observed that under anaerobic condition a tissue or microorganism utilizes more glucose than it does under aerobic conditions.
  • It reflects inhibition of glycolysis by oxygen and is called pasteure effect.
  • The Pasteur effect is due to inhibition of the enzyme phosphofructokinase because of inhibitory effect caused by citrate and ATP, the compounds produced in presence of oxygen due to operation of TCA cycle. Crabtree effect
  • This is opposite of Pasteur effect, which represents decreased respiration of cellular systems caused by high concentration of glucose.
  • When oxygen supply is kept constant and glucose concentration is increased, the oxygen consumption by cells falls, i.e., relative anaerobiosis is produced when glucose concentration is increased in constant supply of oxygen.
  • It is seen in cells that have a high rate of aerobic glycolysis.
  • In such cells the glycolytic sequence consumes much of the available Pi and NAD+, which limits their availability for oxidative phosphorylation.
  • As a result, rate of oxidative phosphorylation decreases, and oxygen consumption also shows a corresponding fall.

Q. 38

Which activate Kinase of Glycolysis?

 A

a)     ATP

 B

b)    cAMP

 C

c)     Insulin

 D

d)    Glucagon

Q. 38

Which activate Kinase of Glycolysis?

 A

a)     ATP

 B

b)    cAMP

 C

c)     Insulin

 D

d)    Glucagon

Ans. C

Explanation:

Regulation of Carbohydrate Metabolism-

Enzyme

Inducer

Repressor

Activator

Inhibitor

Glycogen synthase

Insulin

Glucagon

Insulin, glucose-6-phosphate

glucagon

Hexokinase

 

Glucagon

 

Glucose-6-phosphate

Glucokinase

Insulin

Glucagon

 

Citrate, ATP, Glucagon

Phosphofructokinase

Insulin

Glucagon

5 AMP, fructose 6-phosphate, fructose 2,6-biphosphate, Inorganic phosphate

 

 

Pyruvate kinase

 

Insulin

 

Glucagon

 

Fructose 1-6- biphosphate, Insulin

 

ATP alanine glucagon norepinephrine

Pyruvate dehydrogenase

Insulin

Glucagon

CoA, NAD+, Insulin, ADP, pyruvate

Acetyl CoA, NADH, ATP

 


Q. 39

ATP is consumed at which stage of Glycolysis?

 A

a)     Enolase

 B

b)    Hexokinase

 C

c)     Pyruvate kinase

 D

d)    Isomerase

Q. 39

ATP is consumed at which stage of Glycolysis?

 A

a)     Enolase

 B

b)    Hexokinase

 C

c)     Pyruvate kinase

 D

d)    Isomerase

Ans. B

Explanation:

ATP is consumed at reactions catalysed by –> à hexokinase, phosphofructokinase I.

Quiz In Between


Q. 40

In glycolysis, the first committed step is catalysed by-

 

 A

a)     2, 3 DGP

 B

b)    Glucokinase

 C

c)  Hexokinase

 D

 

d)    Phosphofructokinase

Q. 40

In glycolysis, the first committed step is catalysed by-

 

 A

a)     2, 3 DGP

 B

b)    Glucokinase

 C

c)  Hexokinase

 D

 

d)    Phosphofructokinase

Ans. D

Explanation:

Phosphofructokinase catalyzes the commited step of glycolysis, meaning that once fructose l, 6 – bisphosphate is formed it must go for the glycolytic pathway only


Q. 41

The rate- limiting enzyme in glycolysis is-

 A

a)     Phosphofructokinase

 B

b)    Glucose 6- dehydrogenase

 C

c)     Glucokinase

 D

d)    Pyruvate kinase

Q. 41

The rate- limiting enzyme in glycolysis is-

 A

a)     Phosphofructokinase

 B

b)    Glucose 6- dehydrogenase

 C

c)     Glucokinase

 D

d)    Pyruvate kinase

Ans. A

Explanation:

Regulatory steps of Glycolysis are-

–         Hexokinase/ Glucokinase

–         Phosphofructokinase

–         Pyruvate kinase


Q. 42

Number of ATP molecules and NADH formed in each cycle of glycolysis?

 A

a)     4 ATP 2NADH

 B

b)    2 ATP 2 NADH

 C

c)     4 ATP 4 NADH

 D

d)    2 ATP 4 NADH

Q. 42

Number of ATP molecules and NADH formed in each cycle of glycolysis?

 A

a)     4 ATP 2NADH

 B

b)    2 ATP 2 NADH

 C

c)     4 ATP 4 NADH

 D

d)    2 ATP 4 NADH

Ans. A

Explanation:

– In glycoslysis 4 ATPs are produced in which 2 ATPs are utilized so a net gain of 2 ATPs

2 NADH molecules are produced.


Q. 43

Final product in anaerobic glycolysis is :

 A

a)     Pyruvate

 B

b)    Acetyl CoA

 C

c)     Lactate

 D

d)    Oxaloacetate

Q. 43

Final product in anaerobic glycolysis is :

 A

a)     Pyruvate

 B

b)    Acetyl CoA

 C

c)     Lactate

 D

d)    Oxaloacetate

Ans. C

Explanation:

the end product for anaerobic glycolysis is lactate

Quiz In Between



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