intro-types-intro of pentose phosphate pathway-pentose phosphate pathway-significance

1. RESPIRATION & PENTOSE PHOSPHATE
PATHWAY
Presented by: prajapati sapana m.
M.sc sem- 2
Botany CBO-501
Department of life
sciences, H.N.G.U.,
patan.

2. CONTENTS
• Introduction of respiration
• Types of respiration
• Introduction of pentose phosphate pathway
• Pentose phosphate pathway
• Significance of pentose phosphate pathway

3. Introduction of respiration
• Defination: Respiration is a process of
biological oxidation where oxygen
is utilized and CO₂ is realesed for
the propose of releasing energy.
 Degradation of organic food for the purpose of
releasing energy can occur with or without the
participation of oxygen.
 The plants possess some different type of respiration
because -
i) The plants lack respiratory system and
respiratory movements,

4. Cont…
ii) The exchange of gases in plants is also different
because during day light respiration is slightly
suppressed due to photosynthesis,
iii)Sometimes the plants do not use oxygen during
respiration(anaerobic),
iv) In some cases CO₂ is not liberated outside the plant
cells.
Due to above four reasons, the physiologists
used the term respiration only for the oxidation of
food materials inside the cell.
 Respiration takes place at normal temperature.
 Hence respiration can be classified into two types:
(1) Aerobic respiration
(2) Anaerobic respiration

5. Types of respiration
1) Aerobic respiration :
 Respiration occurring in presence of oxygen is called
aerobic respiration.
 In most of the plants usually aerobic respiration is
found which is stopped in absence of O₂.
 During aerobic respiration, the food materials like
carbohydrates, fats and proteins are completely
oxidised into CO₂ and H₂O and large amount of energy
is released.

6. Cont…
 The oxidation of one molecule of glucose produces about
673 K. calories of energy.
 It occurs in all living cells of higher plants.
C₆H₁₂O₆ + 6O₂ 6CO₂ + 6H₂O + 673 K.cal
Glucose oxygen carbon water energy
dioxide
 The produced energy is absorbed by ADP and is stored in
the form of ATP.
 The energy is again produced by the hydrolysis of ATP,
when required.

7. Cont…
(2) Anaerobic respiration :
 Respiration occurring in absence of oxygen is called
anaerobic respiration.
 It is found only in certain plants.
 During anaerobic respiration,the food materials like
carbohydrates,fats and proteins are imcompletely
oxidised resulting in the formation of alcohol and CO₂.

8. Cont…
 The energy released during anaerobic respiration is
quite less( about 21 K.cal.per molecule) in
comparison to aerobic respiration.
C₆H₁₂O₆ 2C₂H₅OH + 2CO₂ + 21 K.cal.
glucose alcohol energy
 Anaerobic respiration occurs during resting stage of
seeds, initial stages of seed germination,in the cells
of fruit walls,several micro-organisms and Ascaris etc.

9. Aerobic Anaerobic
1) It occurs in all living cells of higher
plants.
1) It occurs in bacteria,certain
fungi,germinating seeds and fleshy
fruits.
2) It requires oxygen. 2) Oxygen is not required.
3) The oxidation of one molecule of
glucose produces 38 molecules.
3) The number of ATP molecules
produced is only 2.
4) All the reactions except the
reactions of glycolysis take place
inside mitochondria.
4) All the reactions take place in
cytoplasm.
5) Organic compounds ar completely
oxidised and high energy is released.
5)Organic compounds are
incompletely oxidised and very small
amount of energy is released.
6) Not toxic to plants. 6) Toxic to higher plants.
7)The end products are CO₂ and H₂O 7) The end products are alcohol and
CO₂.

10. Introduction of pentose phosphate
pathway
Definition :The pentose phosphate pathway(ppp) is an
alternative pathway for the metabolism of glucose.It
does not generate ATP but produces NADPH and
pentose-5- phosphates and other sugar-phosphates.
 The pentose phosphate pathway also called the hexose
monophosphate pathway(HMP) or phosphogluconate
pathway.
 It occurs in cytosol of the cell.
 HMP shunt is more anabolic in nature.

11. Cont…
 The tissues such as liver,adipose tissue,adrenal
gland,erythrocytes,testes and lactating mammary gland
are highly active in HMP shunt.
 It is concern with the biosynthesis of NADPH and
pentoses.
Reactions of the pathway:
 reaction of the pathway divided into two phases:-
(1)Oxidative phase or irreversible oxidative phase.
(2) non- oxidative or Reversible non-oxidative phase.

12. Pentose phosphate pathway
Oxidative phase :
 The first reaction of the pentose phosphate pathway is
the oxidation of glucose 6-phosphate by glucose 6-
phosphate dehydrogenase (G6PD) to form 6-
phosphogluconolactone,an intramolecular ester.
 NADP⁺ is the electron acceptor, and the overall
equilibrium lies far in the direction of NADPH formation.

13. Cont…
 The lactone is hydrolyzed to the free acid 6-
phosphogluconate by a specific lactonase,then 6-
phosphogluconate undergoes oxidation and
decarboxylation by 6-phosphogluconate
dehydrogenase to form the Ketopentose ribulose 5-
phosphate.
 This reaction generates a second molecule of NADPH.
 Phosphopentose isomerase converts ribulose 5-
phosphate to its aldose isomer , ribose 5- phosphate.

14. Cont…
 In this pathway glucose 6-phosphate is directly oxidized
without entering glycolysis,hence it is also known as
direct oxidation pathway or hexose monophosphate
shunt.
 Glucose 6-phosphate + 2NADP⁺ + H₂O
ribose 5-phosphate +CO₂ + 2NADPH +2H⁺
 The net result is the production of NADPH,a reductant
for biosynthetic reactions,and ribose 5-phosphate,a
precursor for nucleotide synthesis.

15. Cont…

16. Non-oxidative phase
• The non-oxidative reaction of pentose phosphate
pathway catalyzes the inter-conversion of 3,4,5,7
carbon sugars.
• The non-oxidative phase of the pentose phosphate
pathway is initiated when the cell needs more NADPH
than ribose 5-phosphate.
• In this second process are a complex sequence of
reactions that let you change the C3,C4,C5,C6,and C7
pentose sugars to form finally glyceraldehyde-3-
phosphate and fructose 6-phosphate,which can go
directly to glycolysis.

17. Cont…
Step 1: (Epimerization)
 Ribulose-5- phosphate is converted into xylulose-5-
phosphate in the presence of the enzyme
“phosphopentose epimerase”.
Step 2:(Isomerization )
 Ribulose-5-phosphate is isomeriss into Ribose-5-
phosphate by the enzyme “phosphopentose
isomerase”.

18. Cont…
 Step 3: (Transketolation)
• Transketolase is responsible for the cleving of a two
carbon unit from xylulose-5-phosphate and adding that
two carbon unit to ribose-5-phosphate thus resulting in
glyceraldehyde-3-phosphate and sedoheptulose-7-
phosphate.
• Here, TPP(Thiamine pyrophosphate) acts as a co-enzyme.
Step 4: (Transaldolation)
• When sedoheptulose-7-phosphate reacts with
glyceraldehyde-3-phosphate it gives 4 carbon compound
erythrose-4-phosphate & 6 carbon compound Fructose-
6-phosphate by the Transaldolase enzyme.

19. Cont…
• In this reaction first 3 carbons of sedoheptulose-7-
phosphate is shifted to the aldehyde group of the
Glycerldehyde-3-phosphate ,which will form the tetrose
erythrose-4-phosphate
Step 5: (Transketolation)
• Now,transketolase enzyme acts again,forming fructose-6-
phosphate & glyceraldehyde-3-phosphate form erythrose
4-phosphate and xylulose 5-phosphate.
• Then, again transketolase enzyme transferring a C2
unit,from xylulose-5-phosphate to erythrose-4-
phosphate,thus form another molecule of fructose-6-
phosphate and glyceraldehyde-3-phosphate,both are
intermediates of glycolysis.
• Thus the phase of this pathway is closed.

20. Cont…

21. Signification of P.P.P
1. It provides alternative route for carbohydrate
breakdown
2. It generates NADPH molecules which are used as
reductans in biosynthetic processes under condition
when NADPH molecules are not generated by
photosynthesis.
3. It is therefore,especially important in non-
photosynthetic tissues such as in differentiating
tissues,germinating seeds and during periods of
darkness.production of NADPH is not linked to ATP
generation in pentose phosphate pathway.

22. Cont…
3.It provides ribose sugars for the synthesis of nucleic
acids.
4.It important role in fixation of CO₂ in photosynthesis
through ribulose-5-phosphate.(ribulose 1,5-
biphosphate derived from ribulose-5-phosphate is
the primary accepter of CO₂ in photosynthesis).
5.It provides erythrose-4-phosphate which is required
for the synthesis of shikimic acid. the latter is
precursor of aromatic ring compounds.

24. Cont…
References:
• Principles of biochemistry by- albert leningher
• A textbook of plant physiology,biochemistry &
biotechnology by – s.k.verma & mohit verma
• https://slideshare.net
• www.biologydiscussion.com