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
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