PLANT RESPIRATION.pptx

PLANT RESPIRATION
Respiration-Detail understanding along with regulation and
factors w.s.r to Energy Production.
By
N. Sannigrahi, Associate Professor,
Department of Botany,
Nistarini College, Purulia (W.B) India

RESPIRATION-CATABOLISM
 Energy is defined as the capacity to do work. The living
objects require continuous supply of free energy for the
following purposes-
 To synthesize macromolecules from simpler and smaller
precursors,
 To transport molecules and ions across membranes
against gradients,
 To perform mechanical work as phloem transport,
 To ensure fidelity of information.
 The free energy in these process derived from
environment by phototrophs and chemotrophs ( energy
by the oxidation of food stuffs). The special carrier for
the energy is ATP and this ATP donates much of its
energy for the aforesaid processes.

ATP-UNIVERSAL ENERGY CURRENCY
 According to Lipmann(1941), ATP is the primary and
universal carrier of chemical energy and it renews
through ATP cycle. ATP and its successive hydrolysis
products ADP & AMP are nucleotide and all of them
occur both in cytosol and mitochondria along with
nucleus.ATP serves as the principal intermediate donor
of free energy in biological systems rather than storage
form and its turnover rate is very high. When ATP is
hydrolyzed, it loses its terminal ℽ phosphate group to
form ADP and Pi.
 ATP+H2O=ADP + Pi
 The standard free energy change , ∆ G∙ for this reaction
is -7.3 Kcal/mol. Thus ATP plays a very crucial role in
this regard to drive different types of biological
pathways. During the respiration, the main objective is
the production of ATP mostly by the oxidation of the
substrates enzyme mediated pathways.

RESPIRATION
 This is a process by which living cells break down
complex high energy food molecules into simple low
energy molecules, i.e., CO2 and H2O, releasing the
energy trapped within the chemical bonds. The energy
released during oxidation of energy rich compounds is
made available for activities of cells through an
intermediate compound called adenosine triphosphate
(ATP).
 During process of respiration, the whole of energy
contained in respiratory substrates is not released all at a
time. It is released slowly in several steps of reactions
controlled by different enzymes.
 Carbohydrates is the first cellular constituents formed by
the photosynthetic organisms by the carbon assimilation
pathways followed by vast array of other organic
compounds used as substrates for ATP yielding process.

RESPIRATION-WHERE?
 Respiration takes place in all types of living cells, and
generally called cellular respiration. During the process of
respiration oxygen is utilized, and CO2 water and energy
are released as products. The released energy is utilized in
various energy-requiring activities of the organisms, and
the carbon dioxide released during respiration is used for
biosynthesis of other molecules in the cell.
 Here, 686 kcal or 2870 kJ of energy is liberated per
molecule of glucose. Formerly, this calculated value was
673 kcal. One kcal is equal to 1000 calories. This means
that one molecule of glucose on complete oxidation yields
686 kcal (kilocalories) of energy, (i.e., 686, 000 calories).
 This entire process is governed by a number of
intermediates driven by enzymes.

OVERALL PROCESS OF RESPIRATION
 The main facts associated with respiration are:
 a. Consumption of atmospheric oxygen.
 b. Oxidation and decomposition of a portion of the stored
food resulting in a loss of dry weight as seen in the seeds
germinating in dark.
 c. Liberation of carbon dioxide and a small quantity of
water (the volume of CO2 liberated is equal to volume of
O2 consumed).
 d. Release of energy by breakdown of organic food,
(such as carbohydrates).
 Carbohydrate is mainly used by the cells as glucose
along with fructose and galactose during respiration. But
pentose sugars like arabinose, ribose and xylose may be
used but their fate after absorption is obscure.

RESPIRATORY SUBSTRATES
 Respiratory substrates are those organic substances
which are oxidized during respiration. They are high
energy compounds and are called respiratory substrates.
They may be carbohydrates, fats and proteins.
Carbohydrates, such as glucose, fructose (hexoses),
sucrose (disaccharide) or starch, inulin, hemicelluloses
(polysaccharide), etc., are main respiratory substrates.
Besides, fats are used as respiratory substrates by a
variety of organisms as they contain more energy than
carbohydrates.
 In rare circumstances, when carbohydrate reserves are
exhausted, fats and proteins also serve as respiratory
substrates. Blackman termed the respiratory oxidation of
protoplasmic protein as protoplasmic respiration, while
oxidation of carbohydrates as floating respiration.

TYPES OF RESPIRATION
 There are two main types of respiration depending upon the
availability of oxygen as terminal electron acceptor. It also
plays an important role for the generation of the energy by the
complete or incomplete oxidation of the substrate.
 (i) Aerobic-where oxygen is available,
 (ii) Anaerobic- in absence of oxygen in the vicinity.
 (i) Aerobic Respiration:
 This type of respiration leads to a complete oxidation of
stored food (organic substances) in the presence of oxygen,
and releases carbon dioxide, water and a large amount of
energy present in respiratory substrate. Such type of
respiration is generally found in higher organisms.
 The overall equation is:
 C6H12O6+ 6O2= 6CO2 + 12 H2O-∆

ANAEROBIC RESPIRATION
 Anaerobic respiration:
 This type of respiration occurs in complete absence of
oxygen. In the absence of free oxygen, many tissues of
higher plants, seeds in storage, fleshy fruits, and succulent
plants, such as cacti temporarily take to a kind of
respiration, called anaerobic respiration. Such respiration
generally occurs in lower organisms like bacteria and fungi.
 This results in incomplete oxidation of stored food and
formation of carbon dioxide and ethyl alcohol, and
sometimes also various organic acids, such as malic, citric,
oxalic, tartaric, etc. Very little energy is released by this
process to maintain activity of protoplasm. Very lesser to
least amount of energy is produced along with the different
end products depending upon the enzyme catalyzed the
process. Mostly ethyl alcohol or lactic acid or other
products are produced along with carbon-di-oxide.

PHASES OF AEROBIC RESPIRATION
 There are three major phases of respiration:
 (i) Glycolysis, and
 (ii) Krebs cycle.
 Iii) Terminal respiration via ETC
 During process of respiration, carbohydrates are
converted into pyruvic acid through a series of enzymatic
reactions. This series of reactions is known as glycolysis
which takes place in cytosol.
 Now, pyruvic acid enters mitochondria, where several
enzymes catalyse the reactions, and pyruvic acid finally
converts into CO2 and water. This series of enzymatic
reactions is known as Krebs cycle (after name of its
discoverer Sir Hans Adolf Krebs (1900-1981), awarded
Nobel Prize in 1953), or tricarboxylic acid (TCA) or
citric acid cycle.

GLYCOLYSIS
 Glycolysis is a term used to describe the sequential series of
reactions present in a wide variety of tissues that starts with
a hexose sugar (usually glucose) and ends with pyruvic
acid. This term has originated from Greek words, glycos =
sugar and lysis = splitting.
 The scheme of glycolysis was discovered by three German
Scientists, Gustav Embden, Otto Meyerhof and J. Parnas,
and therefore, referred as EMP pathway, after the
abbreviation of their last names.
 Glycolysis is the first stage in the breakdown of glucose and
is common to all organisms. This means, glycolysis is
common to both aerobic and anaerobic modes of
respiration. In anaerobic organisms, this is only process in
respiration. Glycolysis occurs in cytoplasm of cells. During
this process, glucose undergoes partial oxidation to form
two molecules of pyruvic acid.

PATHWAY OF GLYCOLYSIS
 In plants, glucose is derived from sucrose, which is the end
product of photosynthetic carbon reactions (also known as
dark reactions) or from storage carbohydrates.
 Sucrose is converted into glucose and fructose by the
enzyme invertase. Now, these two monosaccharide (i.e.,
glucose and fructose) enter glycolysis or EMP pathway. It is
mainly comprises of two phases-preparatory & pay off
phases
 PREPARATORY PHASE: Here energy is consumed to
convert glucose into three –carbon sugar phosphates(G-3-P)
 Phosphorylation of Sugar (i.e., First Phosphorylation):
 Glucose and fructose are phosphorylated to give rise to
glucose-6-phosphate and fructose-6-phosphate, respectively,
by the activity of enzyme hexokinase, in presence of ATR
The phosphorylated form of glucose then isomerises to
produce fructose-6-phosphate. Isomerisation takes place
with the help of enzyme phosphohexose isomerase.

GLYCOLYSIS
 b. Phosphorylation of Fructose-6-Phosphate (i.e., Second
Phosphorylation):
 Now, fructose-6-phosphate is phosphorylated and
fructose-1, 6-bisphosphate produced by the action of
enzyme phosphofructokinase in presence of ATP.
 The two ATPS are required in presence of Ppi-PFK. It is
also reversible reaction, increasing the flexibility of
glycolytic mechanism.
 C. Splitting: The destabilization of the molecule in the
previous reaction allows the hexose ring to be split by
aldolase into two triose sugars- dihydroxyacetone
phosphate , a ketone and glyceraldehydes 3-phosphate ,
an aldehyde. There are two classes of aldolase- class I
aldolase as in animals ands plants & class II aldolase in
others.
 This process enables to carry forward the next events
required for the same.

PAY OFF PHASE
 The 2nd half of the glycolysis is known as pay-off phase
characterized by a net gain of energy rich molecules ATP &
NADH. Each reaction in the pay-off phase occurs twice per
glucose molecule. This yields 2NADH molecules and 4 ATP
molecules by a number of following pathways.
 DHAP/PGALD is dehydrogenated and inorganic phosphate is
added to them forming 1,3 bisphosphoglycerate.The hydrogen
is used to reduce two molecules of NAD+ to NADH + H+ for
each triose.
 In the next step, the enzymatic transfer of a phosphate group
from 1,3 biphosphoglycerate to ADP by phosphoglycerate
kinase forming ATP and 4-phosphoglycerate. Here first
substrate level phosphorylation takes place. Later on,
phosphoglycerate mutase now form 2-phosphoglycerate.

PAY OFF PHASE
 Enolose next forms phospho-enolpyruvate from 2-
phosphoglycerate in the presence of co-factors include 2Mg2+
ions
 A final substrate-level phosphorylation now forms a molecule
of pyruvate and a molecule of ATP by means of the enzyme
pyruvate kinase. This serves as additional regulatory step,
similar to the phosphoglycerate kinase step. Mg2+ also serves
as cofactor in this regard.
 Thus, it become quite clear that the glycolysis is the lyses of the
hexose sugar by the two important phases-preparatory phase
and the pay off phase. In the first step, the energy is consumed
but in the next step there is an enough provision of the energy
production both by the means of substrate level
phoisphorylation and another by means of the oxidative
phosphoryl;ation.

GLYCOLYSIS-OUTCOME
 (i) During glycolysis two triose phosphate molecules are
formed from one glucose molecule, and 4 ATP molecules
are produced.
 (ii) Out of 4 ATP molecules, 2 ATP molecules are utilised
in first few steps in converting glucose to fructose-1, 6
bisphosphate.
 (iii) Moreover, three ATP molecules are produced from
oxidation of each of two molecules of NADH produced
during catabolism of glucose.
 (iv) In all, a net gain of 8 molecules occurs during
process of glycolysis.
 (v) However, in anaerobic respiration, NADH + H^ is
not converted to ATP, and therefore, only 2 ATP
molecules are produced.

FATE OF PYRUVIC ACID
 (Aerobic Oxidation of Pyruvic Acid)
 Now, pyruvic acid generated in cytoplasm through glycolysis
is transferred to mitochondria. This is initiation of second
phase of respiration. As soon as, pyruvic acid enters the
mitochondria, one of the three carbon atoms of pyruvic acid is
oxidized to carbon dioxide in a reaction called oxidative
decarboxylation.
 Here, pyruvate is first decarboxylated, and thereafter oxidized
by enzyme pyruvate dehydrogenase. This enzyme is made up
of a decarboxylase, lipoic acid, TPP, transacetylase and Mg+2.
Acetyl Co-A acts as substrate entrant for Krebs cycle. The
reaction is coupled with the reduction of NAD+ to NADH. The
reaction is an example of oxidative decarboxylation since the
other product is CO2.Acetryl-CoA is used up in the TCA cycle
and in the production of fatty acids.

REGULATION OF GLYCOLYSIS
 The free energy diagram of glycolysis shown in Figure points
to the three steps where regulation occurs. Remember that for
any reaction, the free energy change depends on two factors:
the free energy difference between the products and reactants
in the standard state and the concentration of the products and
reactants. Remember that at equilibrium the rates of forward
and reverse reactions are equal. Therefore, the conversion of,
example,3‐phosphoglycerate to glyceraldehyde‐3‐phosphate
occurs rapidly. In contrast, the reactions far from equilibrium,
such as the conversion of phosphoenol pyruvate to pyruvate,
have rates that are greater in the forward than in the reverse
direction. Since the reaction is thermodynamically favorable,
the change of the free energy for the step will be negative. A
step with large change in free energy is considered to be easily
regulated.

OXIDATIVE PENTOSE PHOSPHATE PATH

OXIDATIVE PENTOSE PHOSPHATE PATH
 The pentose phosphate pathway (also called the
phosphogluconate pathway and the hexose monophosphate
shunt and the HMP Shunt) is a metabolic pathway parallel to
glycolysis. It generates NADPH and pentose (5-carbon sugars)
as well as ribose 5-phosphate, a precursor for the synthesis of
nucleotides. The pentose phosphate pathway (also known as the
hexose monophosphate (HMP) shunt)) is an important
physiological process that can occur in 2 phases: oxidative and
nonoxidative. The oxidative phase utilizes glucose -6-
phosphate to produce nicotinamide adenine dinucleotide
phosphate (NADPH) and ribulose-5- phosphate (which can be
converted to ribose -5- phosphate ). The nonoxidative phase is
a collection of several reversible reactions in.

OXIDATION OF PYRUVATE TO ACETYL-COA
 which the intermediates are connected to several other
pathways, including nucleotide synthesis , aromatic amino acid
synthesis , and glycolysis.
 1. Pyruvate oxidative decarboxylated to acetyl-CoA (“active
acetate”) before entering the citric acid cycle.
 2. The reaction is catalyzed by the multienzyme complex
consisting of several different enzymes. This complex is known
as pyruvate dehydrogenase complex.
 3. Pyruvate is decarboxylated in the presence of thiamine
pyrophosphate (TPP) to a hydroxymethyl derivative which
reacts with oxidized lipoate to from S-acetyl lipoate being
catalyzed by the enzyme pyruvate dehydrogenase.

PYRUVATE OXIDATION
 4. S-acetyl lipoate reacts with coenzyme A to form acetyl-CoA
and reduced lipoate in presence of di-hydrolipoyl
transacetylase.
 5. The reduced lipoate is re-oxidized by FAD in presence of
dihydrolipoyl dehydrogenase.
 6. Finally, the reduced FAD is oxidized by NAD+. The reduced
NAD (NADH + H+) enters the respiratory chain producing 3
ATP.
 7. The pyruvate dehydrogenase complex consists of about 29
mols of pyruvate dehydrogenase and 8 mols of dihydorlipoyl
dehydrogenase distributed around 1 mol of transacetylase.

REGULATION OF PDH
 1. The increased Pyruvic acid from carbohydrate diet inhibits
pyruvate dehydrogenase kinase for which active pyruvate de-
hydrogenase is formed. This causes the rapid breakdown of
pyruvic acid to form acetyl-CoA.
 2. Acetyl-CoA and NADH formed by enhanced p-oxidation
during starvation and diabetes mellitus activate pyruvate
dehydrogenase kinase decreasing the “active” form of
pyruvate dehydrogenase. Hence, less pyruvic acid is
catabolized and glycolysis is also inhibited
 Inhibitors:
 Arsenitc inhibits pyruvate dehydrogenase and dietary
deficiency of thiamine also allows pyruvate to accumulate.
Chronic alcoholics also suffer from the deficiency of thiamine
which results in the accumulation of pyruvic acid. Lactic
acidosis is caused by the inherited deficiency of pyruvate
dehydrogenase.

NADH SHUTTLE
 Reduced coenzymes such as NADH and NADPH do not
permeate the inner membrane of the mitochondrion to any
significant extent.
 However, reduced pyridine nucleotides are known to be
produced in a number of reactions in the cytosol (the reduction
of NAD+ at the glyceraldehydes step in glycolysis is an
important example) and the re-oxidation of NADH occurs via
the mitochondrion.
 The mechanism involves a set of reactions called a shuttle.
 Glycerol Phosphate Shuttle:
 The glycerol phosphate shuttle involves:
 (1) Glycerol phosphate dehydrogenase in the cytosol,
 (2) Glycerol phosphate dehydrogenase on the outer
surface of the inner mitochondrial membrane, and

NADH SHUTTLE
 3) The reduction of Q in the electron transport chain.
 Dihydroxyacetone phosphate, NADH, and H+ react in the
cytosol to form glycerol phosphate, which diffuses through the
outer mitochondrial membrane to the outer surface of the inner
membrane. There the glycerol phosphate reacts with the
membrane dehydrogenase to form dihydroxyacetone
phosphate, which returns to the cytosol. The membrane-bound
dehydrogenase employs a flavoprotein as a coenzyme, and the
FP becomes reduced during the reaction.
 Subsequently, the electrons from the reduced FP are passed
directly into the electron transport system at the Q step.
Because the NAD+ →FP step of electron transport is skipped,
only two ATP are generated for each pair of electrons that
enters in this fashion from the cytosol.

NADH SHUTTLE
 2. Malate-Aspartate Shuttle:
 Another shuttle, the malate-aspartate shuttle, can also transport
the hydrogen accepted during the reduction of NAD + in the
cytosol across the inner membrane. H+ transported in this
manner into the matrix, enters the electron transport chain via
NADH dehydrogenase, and as a result three ATP are generated
for each pair of electrons.
 The different totals for ATP production (i.e., gross production
of either 38 or 40) depend on which shuttle is used to transport
H+ from NADH into the mitochondrion. H + from the glycerol
phosphate shuttle is accepted by FP and as a result one coupling
step is bypassed. Hydrogen from the malate-aspartate shuttle
enters the electron transport chain earlier, so that all three
coupling sites are utilized.

CITRIC ACID CYCLE
 In aerobic organisms, the TCA cycle or Krebs cycle or Citric
acid cycle is a major enzyme catalyzed chemical conversion
of different respiratory substrates into CO2 and H2O to
generate a form of usable energy. In eukaryotic cells, it takes
place in the matrix of mitochondrion.
 Te Citric acid cycle begins with the transfer of a two carbon
acetyl group from Acetyl CoA to the four carbon acceptor
compound (OAA) in presence of Citrate synthetase to Citric
acid.
 The citrate then goes a series of chemical transformations
losing two carboxyl groups as CO2 and it originate from OAA
not directly from Acetyl Co-A. The entire process takes place
by a series of chemical reactions via cis- Aconitate, Isocitrate,
Oxalo- succinate, Succinyl- CoA, Fumerate in presence of
enzymes like Aconitase, Isocitrate dehydrogenase, Succinyl-
CoA synthetase, Fumarase etc.

CITRIC ACID CYCLE
 However, because of the role of the citric acid cycle in
anabolism, they may not be lost, since many TCA cycle
intermediates are also used as precursors for the biosynthesis
of other molecules.
 Most of the energy made available by the oxidative steps of
the cycle is transferred as energy –rich electrons to NAD+ ,
forming NADH.For each acetyl group that enters the citric
acid cycle, three molecules of NADH are produced.
 Electrons are transferred to the electron acceptor Q forming
QH2,
 At the end of each cycle, the four carbon OAA is regenerated
and the cycle continues in a repeated order to form the same
as a part of energy producing process and as a part of other
biosynthetic pathways.

AMPHIBOLIC CYCLE
 The term amphibolic is used to describe a biochemical
pathway that involves both catabolism and anabolism
Catabolism is a degradative phase of metabolism in which large
molecules are converted into smaller and simpler molecules,
which involves two types of reactions. First, hydrolysis
reactions, in which catabolism is the breaking apart of
molecules into smaller molecules to release energy. Examples
of catabolic reactions are digestion and cellular respiration,
where sugars and fats are broken down for energy. Breaking
down a protein into amino acids, or a triglyceride into fatty
acids, or a disaccharide into monosaccharide are all hydrolysis
or catabolic reactions. Second, oxidation reactions involve the
removal of hydrogen and electrons from an organic molecule

AMPHIBOLIC CYCLE
 The citric acid cycle (Krebs cycle) is a good example of an
amphibolic pathway because it functions in both the
degradative (carbohydrate, protein, and fatty acid) and
biosynthetic processes. The citric acid cycle occurs on the
cytosol of bacteria and within the mitochondria of eukaryotic
cells. It provides electrons to the electron transport chain which
is used to drive the production of ATP in oxidative
phosphorylation Intermediates in the citric acid cycle, such as
oxaloacetate, are used to synthesize macromolecule
constituents such as amino acids, e.g. glutamate and aspartate.
 The first reaction of the cycle, in which oxaloacetate (a four-
carbon compound) condenses with acetate (a two-carbon
compound) to form citrate (a six-carbon compound) is typically
anabolic. The next few reactions, which are intramolecular
rearrangements, produce isocitrate.

AMPHIBOLIC CYCLE
 The following two reactions, namely the conversion of D-
isocitrate to α-Ketoglutarate followed by its conversion to
succinyl-CoA, are typically catabolic. Carbon dioxide is lost in
each step and succinate (a four-carbon compound) is produced.
There is an interesting and critical difference in the coenzymes
used in catabolic and anabolic pathways; in catabolism NAD+
serves as an oxidizing agent when it is reduced to NADH.
Whereas in anabolism the coenzyme NADPH serves as the
reducing agent and is converted to its oxidized form NADP+.
Citric acid cycle has two modes that play two roles, the first
being energy production produced by the oxidative mode, as
the acetyl group of acetyl-coA is fully oxidized to CO2. This
produces most of the ATP in the metabolism of aerobic
heterotrophic metabolism, as this energy conversion in the
membrane structure (cytoplasm membrane in bacteria and
mitochondria in eukaryotes) by oxidative phosphorylation by
moving electron from donor (NADH and FADH2) to the
acceptor O2.

ANAPLEROTIC REACTIONS
 Anaplerotic reactions are those that form intermediates of the TCA
or citric acid cycle. The malate is created by PEP carboxylase and
malate dehydrogenase in the cytosol. Malate, in the mitochondrial
matrix, can be used to make pyruvate (catalyzed by NAD+ malic
enzyme) or oxaloacetic acid, both of which can enter the citric acid
cycle. As this is a cycle, formation of any of the intermediates can be
used to 'top up' the whole cycle. Anaplerotic is of Greek origin,
meaning "to fill up".
 There are 4 reactions classed as anaplerotic, although the production
of oxaloacetate from pyruvate is probably the most important
physiologically.
 The TCA cycle is a hub of metabolism, with central importance
in both energy production and biosynthesis. Therefore, it is
crucial for the cell to regulate concentrations of TCA cycle
metabolites in the mitochondria. Anaplerotic flux must balance
cataplerotic flux in order to retain homeostasis of cellular
metabolism

ANAPLEROTIC REACTIONS
 From To Reaction Notes Pyruvate oxaloacetate pyruvate +
CO2 + H2O + ATP ⟶ {displaystyle longrightarrow }
oxaloacetate + ADP + Pi + 2H+ This reaction is catalysed by
pyruvate carboxylase, an enzyme activated by Acetyl-CoA,
indicating a lack of oxaloacetate. Pyruvate can also be
converted to L-malate, another intermediate, in a similar way.
 Aspartate oxaloacetate - This is a reversible reaction forming
oxaloacetate from aspartate in a transamination reaction, via
aspartate transaminase. Glutamate α-ketoglutarate glutamate +
NAD+ + H2O ⟶ {displaystyle longrightarrow } NH4
+ + α-
ketoglutarate + NADH + H+. This reaction is catalysed by
glutamate-dehydrogenase. β-oxidation of fatty acids succinyl-
CoA - When odd-chain fatty acids are oxidized, one molecule
of succinyl-CoA is formed per fatty acid. The final enzyme is
methylmalonyl-CoA mutase

REGULATION OF TCA CYCLE
 The regulation of TYCA cycle is largely determined by
substrate availability and product inhibition by the following :
 NADH – a product of all dehydrogenases in the TCA cycle
with the exception of succinate dehydrogenase, inhibits
pyruvate dehydrogenase , isocitrate dehydrogenase, ⅋-
ketogluterate dehydrogenase and also citrate synthetase.
 Acetyl-CoA inhibits pyruvate dehydrogenase while succinyl-
CoA inhibits succinyl C0A synthetase and citrate synthetase.
 Calcium activates pyruvate dehydrogenase , isocitrate
dehydrogenase and ⅋-ketogluterate dehydrogenase. This
increased reaction rate of the many steps of the cycle and
therefore increases flux throughout the pathway.
 Citrate is used for feedback inhibition as it inhibits
phosphofructokinase. HIF also plays role in this regulation.

MITOCHONDRIAL ELECTRON TRANSPORT

 Most eukaryotic cells contain mitochondria which produce ATP
from products of the Krebs cycle, fatty acid oxidation and
amino acid oxidation. At the inner mitochondrial membrane,
electrons from NADH and succinate pass through the electron
transport chain to oxygen, which is reduced to water. The ETC
comprises an enzymatic series of electron donors and acceptors.
Each electron donor passes electrons to more electro-negative
acceptor, which in turn donates these electrons to another
acceptor, a process that continues down the series until electrons
are passed to oxygen, the most electronegative and terminal
electron acceptor in the chain. Passage of electron between
donor and acceptor releases energy, which is used to generate
proton gradient across the mitochondrial membrane by actively
pumping protons into the inner-membrane space, producing a
thermodynamic state that has potential to do work.

 Energy obtained through the transfer of electrons down the ETC used
to pump protons from mitochondrial matrix into the inner-membrane
space, creating an electrochemical proton gradient across the inner
mitochondrial (IMM) called ∆Ψ . The electrochemical proton
gradient allows ATP synthase (ATP-ase) to use the flow of H+
through the enzyme back into matrix to generate ATP from ADP and
inorganic phosphate . Complex I (NADH coenzyme Q reductase I)
accepts electrons from Krebs cycle electron carrier nicotinamide
adenine dinucleotide (NADH), and passes them to coenzyme Q
(Ubiquinone, UQ), which also receives electrons from complex II
(Suiccinate dehydrogenase; II). UQ passes electrons to complex III (
Cytochrome bc1 complex; III) , which passes them to cytochrome c
(cyt c). Cyt c passes electrons to Complex IV (Cytochrome c oxidase;
IV), which uses the electrons and hydrogen ions to reduce molecular
oxygen to water. Thus mainly four membrane –bound complexes
have been found embedded in the inner membrane.

OXIDATIVE PHOSPHORYLATION
 Oxidative phosphorylation is the process by which
energy from electron transport chain (respiratory chain)
is used to make ATP, and is the culmination of energy
yielding metabolism in aerobic organisms. Oxidative
phosphorylation involves the reduction of O2 to H2O with
electrons donated by NADH and FADH2, and equally
occurs in light or darkness. Our current understanding of
ATP synthesis is based on chemiosmotic hypothesis first
formulated in 1961 by Peter Mitchell, a British biochemist
who later received the Nobel Prize for this important
contribution. Chemiosmotic hypothesis has been
accepted as one of the great unifying principles of 20th
century biology. It provides insight into not only the
processes of photophosphorylation and oxidative
phosphorylation but also the processes of disparate
energy transductions as active transport across
membranes

 According to chemiosmotic hypothesis the electron
transport chain is organized so that protons move
outward from the mitochondrial matrix to inter-membrane
space and from cytoplasm to periplasmic space passing
across the plasma membrane . Proton movement may
result either from different complexes or from the action
of special proton pumps that derive their energy from
electron transport resulting in proton motive force (PMF)
composed of a gradient of protons and a membrane
potential due to the unequal distribution of charges.
 Generation of Proton Motive Force (PMF):
 When O2 is reduced to H2O after accepting electrons
transferred from electron transport chain, it requires
proton (H+) from the cytoplasm to complete the reactio

 These protons originate from the dissociation of water
into H+ and OH–. The use of H+ in the reduction of O2 to
H2O and the extrusion of H+ outside the membrane
during electron transport chain cause a net accumulation
of OH– on the inside of the membrane.
 Despite their small size, because they are charged,
neither H+ nor OH– freely passes through the membrane,
and so equilibrium cannot be spontaneously restored on
both sides of membrane.
 This non-equilibrium state of H+ and OH– on opposite
sides of the membrane results in the generation of a pH
gradient and an electrochemical potential across the
membrane, with the inside of the membrane (cytoplasm
side) electrically negative and alkaline, and the outside of
the membrane electrically positive and acidic.

 This pH gradient and electrochemical potential cause the
membrane to be energised. The energised state of a
membrane, which is referred to as proton motive force (PMF)
and is expressed in volts, is used directly to drive the formation
of ATP, ion transport, flagellar rotation, and other useful work.
 Proton Motive Force and ATP Synthesis:
 Proton motive force-derived ATP synthesis involves a catalyst,
which is a large membrane enzyme complex called ATP
synthase or ATPase for short .
 (1) A multi-subunit head piece called F1 located on
mitochondrial matrix side (in eukaryotes) and on cytoplasmic
side (in prokaryotes) and
 (2) A proton conducting channel called F0 that resides in the
inner membrane of mitochondrion (in eukaryotes) and in
plasma membrane (in prokaryotes) and spans the membrane.

 The ATP synthesis takes place at the F1/F0 ATPase, which is
the smallest known biological motor. F1, is the catalytic
complex responsible for the inter conversion of ADP + Pi
(inorganic phosphate) and ATP, and consists of five different
polypeptides present as an α3 β3 ϒƐδ complex. F0 is integrated
in the membrane and consists of three polypeptides in an ab2
c12 complex. 3, 3, 2 and 12 denote the numerical numbers of
α, β, b and c, respectively. Many chemicals inhibit the
synthesis of ATP and can even kill cells to sufficiently high
concentrations. Two such classes of chemicals are known
inhibitors and un-couplers. Inhibitors directly block electron
transport chain.
 The antibiotic piericidin competes with coenzyme Q; the
antibiotic antimycin. A blocks electron transport between
cytochromes b, and c, and both carbon monoxide (CO) and
cyanide (CN–) bind tightly to certain cytochromes and prevent
their functioning.

CYNAIDE RESISTANT RESPIRATION
 The Cyanide is a potential poison of cytochrome oxidase. But
certain plants may carry out the cyanide insensitive respiratory
pathway with an alternative pathway of electron transport. In
this process, the electron is received by the ubiquinone from
different sources like complex I, II or external dehydrogenase
and then instead of being transferred to the cytochromes, it
goes to a flavoporotein FPma (EO= +0.02V) and then goes to
O2 via an alternate oxidase X( ferroprotein). It forms H2O2
which breaks by catalase to produce H2O and O2. Through this
pathway is also inhibited by m- chlorobenzhydroxamic acid.
 SIGNIFICANCE: May occur during unfavorable condition,
 Might occur in big trees showing high amount of lignin
deposition during secondary growth, Generates heat in
thermiogenic condition,
 It brings about continuous utilization of NADH and thereby
prevents the feedback inhibition of respiration due to excess

FACTORS OF RESPIRATION
 Respiration consists of a series of reactions that occur primarily
within mitochondria and generated carbon dioxide, water and
energy as a part of enzyme mediated pathway, Several factors
play direct and indirect role in this aerobic breakdown of the
respiratory substrates as follows:
 Tissue age-Generally rate of the cell division and growth is
directly proportional to the respiratory rate. Younger tissues
have higher respiration than the older one so as to ripening of
fruits and fast germinating roots.
 Temperature- The temperature also has direct effect on the rate
of respiration; higher the temperature, the rate of respiration is
higher. The ration between the rate of respiration at t℃ and (t-
10℃) is called Q10 or Vant Hoff’s co-efficient. The change in
temperature has relatively less pronounced effect on respiratory
rate.

 Oxygen- Respiration decreases with decreased available
oxygen, The rate of respiration for most plants peaks around
the normal oxygen level in the atmosphere. In facultative
aerobic organisms, the presence of oxygen reduces the rate of
respiration than the rate at which the respiration occurs in its
absence is called Pasteur effect. Excessive oxygen may retards
the rate of respiration.
 Carbon dioxide- The higher the concentration of carbon
dioxide, lower the rate of respiration. The higher rate of
respiration is found in both directly infected and surrounding
cells.
 Lack of water- Dry tissue has lower respiration than the wet
tissues. Lack of the availability water has negatively affects on
respiration.
 Available sugar- More the sugar, more respiration generally in
plants. But increased sugar substrate may inhibit respiration in
cancerous cells called Crabtree effect.

 Amount of nutrients- The increase in the amount of nutrients
increase the cellular respiration including the different
respiratory substrates. The nutrients go through three processes
in cellular respiration which are glycolysis, Krebs cycle and the
Cytochrome system.
 State of cell- The state of a cell undergoing the cellular
respiration process is a factor that affects the rate of
transforming nutrients into energy. Working cells have higher
cellular respiration in comparison to the dormant cells like
seeds.
 Cell regions- Certain part of the plant cell engage more
respiration than others. Parts of the plant that engage in
activities that require a lot of energy such as leaves, root tips,
will require more oxygen. Plants having least energy
requirement has low respiratory rate.

 Photosynthesis- Photosynthetes whether stored or synthesized
has role on the rate of respiration. At a particular CO2
concentration, or light intensity, the rate of respiration and
photosynthesis become equal is called compensation point.
 Mechanical injury- any type of mechanical injury increases the
rate of cell division due to increase of phytochrome level and
inducing healing of wound. Thus. In these areas, the rate of the
respiration increases.
 Anti-transpirants- The chemical agents that bring the closure of
the stomata are called anti-transpirants like PMA, these
compounds reduce the rate of the gas exchange. As a result, the
rate of respiration decreases.
 Global warming- Increasing carbon dioxide as a part of
outcome of global warming reduces the amount of oxygen in
the air which can negatively affect the rater of transpiration.

 Hormones- Both plant and animal hormones may induce
changes in respiratory rate. The phytohormones like auxin,
Gibberellins induce increase in the rate of cell division and thus
increase the respiratory rate. But ABA induces the stomata
closure and thus reduce the rate of respiration. Animal
hormones like ACTH, GH or the steroid hormones also increase
the rate of respiration.
 In a word, RQ is greatly determined by metabolic rate and the
different external factors that have direct or indirect role in the
rate of the respiration of the both the plants and animal tissues
including the human beings.

THANKS FOR YOUR JOURNEY
 Acknowledgement:
 1. Google for images
 2. Different web pages for content and enrichment,
 3.Plant Physiology- Mukherji & Ghosh
 Applied Plant Physiology- Arup Kumar Mitra
 A text book of Botany- Hait, Bhattacharya & Ghosh
 Plant Physiology-Devlin
 Disclaimer: This presentation has been prepared for
online free study materials for academic domain without
any financial interest.

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