Lecture 7 - Glycolysis and Oxidative Pentose Phosphate Pathway | Plant Metabolism - Botany PDF Download

 Page 1


Glycolysis and Oxidative Pentose Phosphate Pathway 
Institute of Lifelong learning, University of Delhi 
 
0 
                                                                                          
 
Lesson Prepared Under MHRD project “National 
Mission on Education Through ICT” 
Discipline: Botany 
Paper: Plant Metabolism 
National Coordinator: Prof. S.C. Bhatla 
Lesson: Glycolysis and Oxidative Pentose Phosphate 
Pathway 
Lesson Developer: Dr Manju A. Lal 
Department/College: Kirori Mal College 
Lesson Reviewer: Dr Girish Mishra 
Department/College: Botany, University of Delhi 
Language Editor: Vinee Khanna 
Department/College: Department of Genetics, University of 
Delhi South Campus 
Lesson Editor: Dr Rama Sisodia, Fellow in Botany ILLL 
 
 
 
 
 
 
 
Page 2


Glycolysis and Oxidative Pentose Phosphate Pathway 
Institute of Lifelong learning, University of Delhi 
 
0 
                                                                                          
 
Lesson Prepared Under MHRD project “National 
Mission on Education Through ICT” 
Discipline: Botany 
Paper: Plant Metabolism 
National Coordinator: Prof. S.C. Bhatla 
Lesson: Glycolysis and Oxidative Pentose Phosphate 
Pathway 
Lesson Developer: Dr Manju A. Lal 
Department/College: Kirori Mal College 
Lesson Reviewer: Dr Girish Mishra 
Department/College: Botany, University of Delhi 
Language Editor: Vinee Khanna 
Department/College: Department of Genetics, University of 
Delhi South Campus 
Lesson Editor: Dr Rama Sisodia, Fellow in Botany ILLL 
 
 
 
 
 
 
 
Glycolysis and Oxidative Pentose Phosphate Pathway 
Institute of Lifelong learning, University of Delhi 
 
1 
Learning Outcomes 
After reading the lesson the reader should be able to  elucidate the: 
? Important contributions of scientists, who have helped in elucidating the 
glycolytic pathway. 
? The biochemical reactions that occur during glycolysis. 
? Regulation of glycolytic pathway. 
? Fermentation. 
? Oxidative Pentose Phosphate pathway (Hexose Monophosphate Shunt). 
 
 
  
Page 3


Glycolysis and Oxidative Pentose Phosphate Pathway 
Institute of Lifelong learning, University of Delhi 
 
0 
                                                                                          
 
Lesson Prepared Under MHRD project “National 
Mission on Education Through ICT” 
Discipline: Botany 
Paper: Plant Metabolism 
National Coordinator: Prof. S.C. Bhatla 
Lesson: Glycolysis and Oxidative Pentose Phosphate 
Pathway 
Lesson Developer: Dr Manju A. Lal 
Department/College: Kirori Mal College 
Lesson Reviewer: Dr Girish Mishra 
Department/College: Botany, University of Delhi 
Language Editor: Vinee Khanna 
Department/College: Department of Genetics, University of 
Delhi South Campus 
Lesson Editor: Dr Rama Sisodia, Fellow in Botany ILLL 
 
 
 
 
 
 
 
Glycolysis and Oxidative Pentose Phosphate Pathway 
Institute of Lifelong learning, University of Delhi 
 
1 
Learning Outcomes 
After reading the lesson the reader should be able to  elucidate the: 
? Important contributions of scientists, who have helped in elucidating the 
glycolytic pathway. 
? The biochemical reactions that occur during glycolysis. 
? Regulation of glycolytic pathway. 
? Fermentation. 
? Oxidative Pentose Phosphate pathway (Hexose Monophosphate Shunt). 
 
 
  
Glycolysis and Oxidative Pentose Phosphate Pathway 
Institute of Lifelong learning, University of Delhi 
 
2 
Table of Contents 
Chapter: Glycolysis and Oxidative Pentose Phosphate 
Pathway 
? Introduction 
? Overview of respiration 
? Glycolysis 
? Important contributions of the scientists which led to 
elucidation of glycolytic pathway 
? Glycolytic pathway 
? Preparatory phase 
? Payoff phase 
? Regulation of glycolysis 
? Why are glycolytic intermediates phosphorylated 
? Unique features of plant glycolysis 
? Reoxidation of cytosolic NADH 
? Fate of pyruvate 
? Fermentation 
? Pyruvate metabolism in roots growing under anorexia 
conditions 
? Pyruvate metabolism in muscles 
? Significance of fermentation 
? Oxidative pentose phosphate pathway 
? Pathway 
? Significance of the pathway 
? Regulation of oxidative pentose phosphate pathway 
 
 
 
 
 
 
Page 4


Glycolysis and Oxidative Pentose Phosphate Pathway 
Institute of Lifelong learning, University of Delhi 
 
0 
                                                                                          
 
Lesson Prepared Under MHRD project “National 
Mission on Education Through ICT” 
Discipline: Botany 
Paper: Plant Metabolism 
National Coordinator: Prof. S.C. Bhatla 
Lesson: Glycolysis and Oxidative Pentose Phosphate 
Pathway 
Lesson Developer: Dr Manju A. Lal 
Department/College: Kirori Mal College 
Lesson Reviewer: Dr Girish Mishra 
Department/College: Botany, University of Delhi 
Language Editor: Vinee Khanna 
Department/College: Department of Genetics, University of 
Delhi South Campus 
Lesson Editor: Dr Rama Sisodia, Fellow in Botany ILLL 
 
 
 
 
 
 
 
Glycolysis and Oxidative Pentose Phosphate Pathway 
Institute of Lifelong learning, University of Delhi 
 
1 
Learning Outcomes 
After reading the lesson the reader should be able to  elucidate the: 
? Important contributions of scientists, who have helped in elucidating the 
glycolytic pathway. 
? The biochemical reactions that occur during glycolysis. 
? Regulation of glycolytic pathway. 
? Fermentation. 
? Oxidative Pentose Phosphate pathway (Hexose Monophosphate Shunt). 
 
 
  
Glycolysis and Oxidative Pentose Phosphate Pathway 
Institute of Lifelong learning, University of Delhi 
 
2 
Table of Contents 
Chapter: Glycolysis and Oxidative Pentose Phosphate 
Pathway 
? Introduction 
? Overview of respiration 
? Glycolysis 
? Important contributions of the scientists which led to 
elucidation of glycolytic pathway 
? Glycolytic pathway 
? Preparatory phase 
? Payoff phase 
? Regulation of glycolysis 
? Why are glycolytic intermediates phosphorylated 
? Unique features of plant glycolysis 
? Reoxidation of cytosolic NADH 
? Fate of pyruvate 
? Fermentation 
? Pyruvate metabolism in roots growing under anorexia 
conditions 
? Pyruvate metabolism in muscles 
? Significance of fermentation 
? Oxidative pentose phosphate pathway 
? Pathway 
? Significance of the pathway 
? Regulation of oxidative pentose phosphate pathway 
 
 
 
 
 
 
Glycolysis and Oxidative Pentose Phosphate Pathway 
Institute of Lifelong learning, University of Delhi 
 
3 
Introduction 
Any living organism has the capacity to generate energy from the complex 
organic compounds. This process is called respiration. The metabolic energy, 
which is released during the process, is conserved in the form of ATP.  ATP 
molecules are energy currency of the cell and it is in this form, the energy is 
utilized for various biosynthetic reactions of the cell, and also for various cellular 
activities. This includes cell division, cell elongation, ion transport across cell 
membrane, cytoplasmic movements and cytoplasmic transport. In other words 
most of the activities, which occur in the cell, require ATP. So, it becomes 
essential to study the biochemistry of respiration so as to understand how is this 
ATP generated during the processes? 
Besides ATP generation, intermediates of the respiratory pathway serve as the 
precursors for the biosynthesis of various bio molecules in the cell. 
Respiration requires uptake of O
2 
(in aerobic respiration) for the breakdown of 
carbon compounds with the simultaneous release of CO
2
. The most common form 
of carbon compounds translocated in the plants is sucrose. It is translocated in 
the sieve tubes of the phloem tissues from source to sink. Source is the site 
where sucrose is being generated while sinks are the sites where sucrose is being 
catabolized. The reaction for aerobic degradation of sucrose can be written as: 
C
12
H
22
O
11
 + 12 O
2
  --------------- ? 12 CO
2
  + 11 H
2
O 
The reaction is a coupled redox reaction where sucrose is completely oxidized to 
CO
2
and O
2
 is reduced to water. 
The reaction is exergonic reaction. Standard free energy change during the 
reaction is, ? G
o’
 =  -5760 kJ mole
-1
 of sucrose. 
In a green plant, both the processes i.e., photosynthesis and respiration are 
occurring simultaneously in presence of sunlight. Photosynthetic process is 
limited only to green parts of the plant, which are exposed to sunlight, while 
respiration occurs in all parts of the plant and also is independent of the presence 
of sunlight. It has been reported that in some herbaceous plants, 30 – 60 % of 
the photosynthetic products are lost due to respiration. 
Respiration can be i) maintenance respiration or ii) growth respiration. 
Maintenance respiration is the respiration rate, which is required to maintain the 
cellular activities, which the organism requires for its sustenance, but growth will 
Page 5


Glycolysis and Oxidative Pentose Phosphate Pathway 
Institute of Lifelong learning, University of Delhi 
 
0 
                                                                                          
 
Lesson Prepared Under MHRD project “National 
Mission on Education Through ICT” 
Discipline: Botany 
Paper: Plant Metabolism 
National Coordinator: Prof. S.C. Bhatla 
Lesson: Glycolysis and Oxidative Pentose Phosphate 
Pathway 
Lesson Developer: Dr Manju A. Lal 
Department/College: Kirori Mal College 
Lesson Reviewer: Dr Girish Mishra 
Department/College: Botany, University of Delhi 
Language Editor: Vinee Khanna 
Department/College: Department of Genetics, University of 
Delhi South Campus 
Lesson Editor: Dr Rama Sisodia, Fellow in Botany ILLL 
 
 
 
 
 
 
 
Glycolysis and Oxidative Pentose Phosphate Pathway 
Institute of Lifelong learning, University of Delhi 
 
1 
Learning Outcomes 
After reading the lesson the reader should be able to  elucidate the: 
? Important contributions of scientists, who have helped in elucidating the 
glycolytic pathway. 
? The biochemical reactions that occur during glycolysis. 
? Regulation of glycolytic pathway. 
? Fermentation. 
? Oxidative Pentose Phosphate pathway (Hexose Monophosphate Shunt). 
 
 
  
Glycolysis and Oxidative Pentose Phosphate Pathway 
Institute of Lifelong learning, University of Delhi 
 
2 
Table of Contents 
Chapter: Glycolysis and Oxidative Pentose Phosphate 
Pathway 
? Introduction 
? Overview of respiration 
? Glycolysis 
? Important contributions of the scientists which led to 
elucidation of glycolytic pathway 
? Glycolytic pathway 
? Preparatory phase 
? Payoff phase 
? Regulation of glycolysis 
? Why are glycolytic intermediates phosphorylated 
? Unique features of plant glycolysis 
? Reoxidation of cytosolic NADH 
? Fate of pyruvate 
? Fermentation 
? Pyruvate metabolism in roots growing under anorexia 
conditions 
? Pyruvate metabolism in muscles 
? Significance of fermentation 
? Oxidative pentose phosphate pathway 
? Pathway 
? Significance of the pathway 
? Regulation of oxidative pentose phosphate pathway 
 
 
 
 
 
 
Glycolysis and Oxidative Pentose Phosphate Pathway 
Institute of Lifelong learning, University of Delhi 
 
3 
Introduction 
Any living organism has the capacity to generate energy from the complex 
organic compounds. This process is called respiration. The metabolic energy, 
which is released during the process, is conserved in the form of ATP.  ATP 
molecules are energy currency of the cell and it is in this form, the energy is 
utilized for various biosynthetic reactions of the cell, and also for various cellular 
activities. This includes cell division, cell elongation, ion transport across cell 
membrane, cytoplasmic movements and cytoplasmic transport. In other words 
most of the activities, which occur in the cell, require ATP. So, it becomes 
essential to study the biochemistry of respiration so as to understand how is this 
ATP generated during the processes? 
Besides ATP generation, intermediates of the respiratory pathway serve as the 
precursors for the biosynthesis of various bio molecules in the cell. 
Respiration requires uptake of O
2 
(in aerobic respiration) for the breakdown of 
carbon compounds with the simultaneous release of CO
2
. The most common form 
of carbon compounds translocated in the plants is sucrose. It is translocated in 
the sieve tubes of the phloem tissues from source to sink. Source is the site 
where sucrose is being generated while sinks are the sites where sucrose is being 
catabolized. The reaction for aerobic degradation of sucrose can be written as: 
C
12
H
22
O
11
 + 12 O
2
  --------------- ? 12 CO
2
  + 11 H
2
O 
The reaction is a coupled redox reaction where sucrose is completely oxidized to 
CO
2
and O
2
 is reduced to water. 
The reaction is exergonic reaction. Standard free energy change during the 
reaction is, ? G
o’
 =  -5760 kJ mole
-1
 of sucrose. 
In a green plant, both the processes i.e., photosynthesis and respiration are 
occurring simultaneously in presence of sunlight. Photosynthetic process is 
limited only to green parts of the plant, which are exposed to sunlight, while 
respiration occurs in all parts of the plant and also is independent of the presence 
of sunlight. It has been reported that in some herbaceous plants, 30 – 60 % of 
the photosynthetic products are lost due to respiration. 
Respiration can be i) maintenance respiration or ii) growth respiration. 
Maintenance respiration is the respiration rate, which is required to maintain the 
cellular activities, which the organism requires for its sustenance, but growth will 
Glycolysis and Oxidative Pentose Phosphate Pathway 
Institute of Lifelong learning, University of Delhi 
 
4 
not take place. However, new tissues will be formed at the expense of energy 
produced during growth respiration. In growth respiration energy released during 
respiration is much more than actually required for only maintenance of the 
organism. 
Respiration rate can be measured at the organism level, which means the 
exchange of gases in between the organism and the environment. It is called 
organismal respiration. The biochemical activity, which occurs at the cellular level 
and makes it possible for organismal respiration to happen, is called cellular 
respiration. We will be studying about cellular respiration. 
Overview of respiration 
Respiration is an energy releasing multistep process. If sufficient energy is 
released during a reaction, it can be conserved in the form of ATP. Respiration 
may occur in presence or in absence of O
2
. Generally the plants are growing in 
presence of atmospheric O
2
 (21%). This amount of O
2
 is sufficient to carry out 
the aerobic respiration without showing any limiting effect of O
2 
on the rate of 
respiration. So, plants normally do not grow in deficiency of O
2
. However, in the 
water logged soil conditions or the roots growing deep in the soil, oxygen supply 
may become limiting, creating anorexia (the absence of O
2
) or hypoxia 
(abnormally low O
2
) conditions for the plant roots. In such case either the plant 
develops aerenchyma, a plant cell death controlled development in roots, to 
ensure O
2 
supply, or anaerobic respiration may occur in the plant roots. 
In order to understand the respiration process we will be studying both aerobic 
and anaerobic respiration in plants. 
To understand the respiration process, we will be studying the process under the 
following heads: 
1. In the first lesson we will be studying glucose metabolism, which occurs in 
cytoplasm. This includes the study of glycolytic reactions (conversion of 
glucose to pyruvate), fermentation (conversion of pyruvate to either lactic 
acid or alcohol) and oxidative Hexose Monophosphate Shunt.  
2. The second lesson will include pyruvate metabolism in presence of O
2
, 
which will include, oxidative decarboxylation of pyruvate and Tri Carboxylic 
Acid cycle, which occurs inside the mitochondrial matrix. 
3. The third lesson will include oxidation of the reduced coenzymes (e.g., 
NADH, FADH
2
), which are produced during TCA, by the electron transport 
chain localized in the inner mitochondrial membrane. It is during this phase