Bioenergetics respiration photosynthesis

1. BIOENERGENTICS
RESPIRATION AND PHOTOSYNTHESIS
Bioenergetics is the branch of biochemistry that focuses on
how cells transform energy, often by producing, storing or
consuming adenosine triphosphate (ATP). Bioenergetic
processes, such as cellular respiration or photosynthesis, are
essential to most aspects of cellular metabolism, therefore to
life itself.

2. The metabolic pathway can be either catabolic or anabolic.
Catabolic pathway: is the process that release energy by
breaking down complex molecules to simpler ones.
Example: cellular respiration.
Anabolic pathway: consumes energy to build complicated
molecules from simpler ones.
Example: the synthesis of proteins from amino acids.
Energy is fundamental to all metabolic processes.
Energy released from reactions of catabolic pathways can be
stored and then used to drive reactions of anabolic pathways.

3. The structure and hydrolysis of ATP
ATP (adenosine triphosphate) is the molecule that releases free
energy when its phosphate bonds are hydrolyzed. This energy
is used to drive endergonic reactions in cells.
It contains the sugar ribose, with the nitrogenous base adenine
and a chain of three phosphate groups bonded to it.
The bonds between the phosphate groups of ATP can be
broken by hydrolysis.
ATP + H2O ADP + Pi + Energy
this reaction is exergonic and releases free energy.

5. ATP
Adenosine triphosphate (ATP) is an organic compound that provides energy to
drive many processes in living cells, e.g. muscle contraction, nerve impulse
propagation, condensate dissolution, and chemical synthesis. Found in all known
forms of life, ATP is often referred to as the "molecular unit of currency" of
intracellular energy transfer. When consumed in metabolic processes, it converts
either to adenosine diphosphate (ADP) or to adenosine monophosphate (AMP).
Other processes regenerate ATP so that the human body recycles its own body
weight equivalent in ATP each day. It is also a precursor to DNA and RNA, and is
used as a coenzyme.
ATP + H2O → ADP + Pi ΔG° =7.3 kcal/mol)
ATP + H2O → AMP + PPi ΔG° =10.9 kcal/mol)

6. Photosynthesis
Photosynthesis: conversion of sunlight energy to
chemical energy stored in sugar.
Autotrophs: self-feeders organisms, produce their own
organic molecules (producers).
Heterotrophs: organisms that live on compounds
produced by other organisms (consumers).
6CO2+6H2O-----light, chlorophyll----→ C6H12O6+6O2
Carbon dioxide+ water------→ sugar+ oxygen

7. Chloroplasts: the site of photosynthesis
Chloroplast: found in all plant cells, but leaves are the major site
where photosynthesis occur
Chlorophyll: is the green pigment which gives the leaves their
color.
The chlorophyll is in the membranes of thylakoids (connected
sacs in the chloroplast).
Chloroplast are found mainly in the cells of Mesophyll (the
tissue in the interior of a leaf).

8. Figure 10.3, page
187; Zooming in
on the location of
photosynthesis in
a plant mesophyll
cell.

9. Pigments involved in Photosynthesis
• Chlorophyll a : (Bright or blue green in
chromatograph).
• Major pigment, act as a reaction center,
involved in
trapping and converting light into chemical
energy
• Chlorophyll b : (Yellow green)
• Xanthophyll : (Yellow)
• Carotenoid : (Yellow to yellow-orange)
• In the blue and red regions of spectrum
shows higher rate
of photosynthesis.

10. Stages of Photosynthesis
Two stages are involved in photosynthesis process:
1- Light reaction 2- Calvin cycle
1-Light reaction
Process which takes place in the presence of light only.
Light reactions or the ‘Photochemical ‘phase includes light absorption, splitting of
water, evolution of oxygen and formation of high energy compound like ATP and
NADPH. • It involves several complex & the pigments of the complex are organized
into two discrete photochemical light harvesting complexes (LHC)- Photosystem I
(PS I) and Photosystem II (PS II).
• Light Harvesting Complexes (LHC) : The light harvesting complexes are made up of
hundreds of pigment molecules bound to protein within the photosystem I (PSI)
and photosystem II (PSII)

11. Each photosystem has all the pigments bound to protein
except one molecule of chlorophyll ‘a’ forming a light
harvesting system (antennae).
• Pigments absorbs different wavelength of light for
efficient photosynthesis
• The reaction center (chlorophyll a) is different in both
the photosystems.
• Photosystem I (PSI) : Chlorophyll ‘a’ has an absorption
peak at 700 nm (P700).
• Photosystem II (PSII) : Chlorophyll ‘a’ has absorption
peak at 680 nm (P680)

12. Component of light reaction
Chlorophyll
Accessory pigments(light absorbing pigment other then red or
blue)
Sun light (blue and red wavelength)
PSII(photosystem II)( p680,reaction center, antenna, PEA)
PSI (Photosystem I)(p700, reaction center and antenna, PEA)
ETC( PQ Plastoquinone (PQ) is an electron carrier that plays an essential role in
photosynthesis where it is involved in linear and alternative electron flows., Cytb6f,
Cytochrome b6f (cytb6f) lies at the heart of the light-dependent reactions of oxygenic photosynthesis,
where it serves as a link between photosystem II (PSII) and photosystem I (PSI) through
the oxidation and reduction of the electron carriers plastoquinol (PQH2) and plastocyanin (Pc). PC
Plastocyanin is a blue copper protein which is located in the lumen of the thylakoid where
it functions as a mobile electron carrier shuttling electrons from cytochrome f to P700 in
Photosystem I. FD Ferredoxin electron carrier)
ATP Synthase

13. The light reactions (in the thylakoids):
• Split H2O
• Electron required for Electron transport system is fulfilled by splitting of water-
Photolysis- associated with PS II
• • PS-II loose electrons continuously, filled up by electrons released due to
photolysis of water.
• • Water is split into H+ , (O) and electrons in presence of light and Mn2+ and Cl- .
• • This also creates O2 the bi-product of photosynthesis.
• • Photolysis takes place in the vicinity of the PS-II
• Release O2
• Pathway( Z scheme)
• Reduce NADP+ to NADPH
• Generate ATP from ADP by phosphorylation adding
phosphate group (Pi) to ADP(adenosine diphosphate).

15. Photophosphorylation
• The process of formation of high-energy chemicals (ATP and
NADPH) in the presence of light
• Also defined as – Photophosphorylation is the synthesis of
ATP from ADP and inorganic phosphate in the presence of
light.
• Phosphorylation is the process by which living organisms
extract energy from oxidisable substances and store this in
the form of bond energy like ATP
• Phosphorylation takes place inside the cell in mitochondria &
chloroplast
• It is of two types:
1. Cyclic photophosphorylation
2. Non- cyclic photophosphorylation

16. Cyclic phosphorylation
The photophosphorylation process which results in the movement of the
electrons in a cyclic manner for synthesizing ATP molecules is called cyclic
photophosphorylation.
In this process, plant cells just accomplish the ADP to ATP for immediate energy
for the cells. This process usually takes place in the thylakoid membrane and
uses Photosystem I and the chlorophyll P700.
During cyclic photophosphorylation, the electrons are transferred back to P700
instead of moving into the NADP from the electron acceptor. This downward
movement of electrons from an acceptor to P700 results in the formation of ATP
molecules.

17. Non- Cyclic Photophosphorylation:
•Two photosystems work in series – First PSII and
then PSI.
•These two photosystems are connected through an
electron
transport chain (Z. Scheme).
•ATP and NADPH + H+
are synthesized by this process. PSI
and PSII are found in lamellae of grana, hence this
process is carried here.
Cyclic photophosphorylation :
•Only PS-I works, the electron circulates within the
photosystem.
•It happens in the stroma lamellae (possible
location) because in this region PS-II and NADP
reductase enzyme are absent.
•Hence only ATP molecules are synthesized

18. Cyclic Photophosphorylation Non-Cyclic Photophosphorylation
Only Photosystem I is involved. Both Photosystem I and II are involved.
P700 is the active reaction centre. P680 is the active reaction centre.
Electrons travel in a cyclic manner. Electrons travel in a non – cyclic manner.
Electrons revert to Photosystem I Electrons from Photosystem I are
accepted by NADP.
ATP molecules are produced. Both NADPH and ATP molecules are
produced.
Water is not required. Photolysis of water is present.
NADPH is not synthesized. NADPH is synthesized.
Oxygen is not evolved as the by-product Oxygen is evolved as a by-product.
This process is predominant only in
bacteria.
This process is predominant in all green
plants.
Difference btw cyclic and non cyclic phosphorylation

19. Substrate-level phosphorylation means that a
phosphate is transferred to ADP from a high-energy
phosphorylated organic compound. We will see in the
section on metabolic pathways that a couple of the
enzymes in glycolysis make ATP through substrate-level
phosphorylation, as well as an enzyme in the citric acid
cycle. However, only a small amount of ATP is made this
way in cells undergoing respiration
Substrate-level phosphorylation transfers
phosphate from a phosphorylated organic
compound to ADP to make ATP.
Oxidative phosphorylation synthesizes the bulk of a
cell’s ATP during cellular respiration. A proton-motive
force, in the form of a large proton concentration
difference across the membrane, provides the energy for
the membrane-localized ATP synthase (a molecular
machine) to make ATP from ADP and inorganic
phosphate (Pi). The proton gradient is generated by a
series of oxidation-reduction reactions carried out by
protein complexes that make up an electron transport
chain in the membrane. The term oxidative
phosphoryation, then, refers to phosphorylation of ADP to
ATP coupled to oxidation-reduction reactions.
Oxidative phosphorylation uses the energy from a membrane
proton gradient to power ATP synthesis from ADP and
inorganic phosphate

20. The electron transport chain takes electrons from reduced electron carriers
(NADH) and passes them to a terminal electron acceptor (O2), and uses
the free energy released to generate a membrane proton gradient. Note
that the ATP synthase is not part of the electron transport chain, but is
shown here because it uses the proton gradient to power ATP synthesis.
The ETC builds up the proton gradient, while the ATP synthase discharges
the proton gradient in the process of making ATP.
Chemiosmosis Definition
What is chemiosmosis? In biology, chemiosmosis refers to the process of
moving ions (e.g. protons) to the other side of a biological membrane, and
and as a result, an electrochemical gradient is generated. This can then be
used to drive ATP synthesis. The gradient also incites the ions to
return passively with the help of the proteins embedded in the
membrane. By “passively”, it means that the ions will move from an area
of higher concentration to an area of lower concentration.This process is
similar to osmosis where water molecules move passively. In the case of
chemiosmosis, though, it involves the ions moving across the membrane;
in osmosis, it is the water molecules. Nevertheless, both processes require
require a gradient. In osmosis, this is referred to as an osmotic gradient.
The differences in the pressures between the two sides of the membrane
drive osmosis. As for chemiosmosis, the movement of ions is driven by
an electrochemical gradient, such as a proton gradient.
Chemiosmotic Hypothesis
• The chemiosmotic hypothesis has been put forward to
explain the mechanism of ATP synthesis which is linked to
development of a proton gradient across membranes of
the thylakoid.
• Here the proton accumulation takes place towards the
inside of the membrane, i.e., in the lumen.
• The protons that are produced by the splitting of water are
accumulated inside of membrane of thylakoids (in lumen).
• As the electron moves through the photosystem, protons
are transported across the membrane

21. Figure 10.5; an overview of photosynthesis: cooperation of the light reactions and
the Calvin cycle.

22. How ATP & NADPH is used?
• ATP, NADPH and O2
are the products of light reaction.
diffuses out of the chloroplast while ATP and NADPH
are used to drive the processes leading to the synthesis of
food, i.e., sugars- biosynthetic phase of photosynthesis.
• This process does not directly depend on the presence of
light but is dependent on the products of the light reaction,
i.e., ATP and NADPH, besides CO2
and H2O.
• Melvin Calvin after world war II worked with radioactive 14C
& studied algal photosynthesis which led to the discovery
that the first CO2
fixation product was a 3-carbon organic
acid- 3-phosphoglyceric acid/ PGA

23. He explained complete biosynthetic pathway & named
that as Calvin cycle
• Further work of scientists led to the discovery of another
set of plants in which the first stable product of CO2
fixation
was 4 carbon acid- oxaloacetic acid or OAA.
• Accordingly those plants in which the first product of CO2
fixation is a C3
acid (PGA)- C3
pathway, and those in
which the first product was a C4 acid (OAA)- C4
pathway

24. In plants, carbon dioxide CO2enters the interior of
a leaf via pores called stomata and diffuses into
the stroma of the chloroplast—the site of
the Calvin cycle reactions, where sugar is
synthesized. These reactions are also called
the light-independent reactions because they are
not directly driven by light.
In the Calvin cycle, carbon atoms
from CO2 are fixed (incorporated into organic
molecules) and used to build three-carbon sugars.
This process is fueled by, and dependent on, ATP
and NADPH from the light reactions. Unlike the
light reactions, which take place in the thylakoid
membrane, the reactions of the Calvin cycle take
place in the stroma (the inner space of
chloroplasts).

25. 2-Calvin Cycle
Stages of C3 Cycle
Calvin cycle or C3 cycle can be divided into three main stages:
Carbon fixation
The key step in the Calvin cycle is the event that reduces CO2.
CO2 binds to RuBP in the key process called carbon fixation, forming
two-three carbon molecules of phosphoglycerate. The enzyme that
carries out this reaction is ribulose bisphosphate
carboxylase/oxygenase, which is very large with a four-subunit and
present in the chloroplast stroma. This enzyme works very sluggishly,
processing only about three molecules of RuBP per second (a typical
enzyme process of about 1000 substrate molecules per second). In a
typical leaf, over 50% of all the protein is RuBisCO. It is thought to be
the most abundant protein on the earth.
Reduction
It is the second stage of Calvin cycle. The 3-PGA molecules created
through carbon fixation are converted into molecules of simple sugar –
glucose.
This stage obtains energy from ATP and NADPH formed during the
light-dependent reactions of photosynthesis. The fixation of six molecules
of CO2 and 6 turns of the cycle are required for the removal of one molecule of
glucose from the pathway .This step is known as reduction since electrons
are transferred to 3-PGA molecules to form glyceraldehyde-3
phosphate.
Regeneration
It is the third stage of the Calvin cycle and is a complex process that
requires ATP. In this stage, some of the G3P molecules are used to
produce glucose, while others are recycled to regenerate the RuBP
acceptor. For every CO2 molecule entering the Calvin cycle, 3 molecules of ATP
and 2 of NADPH are required.

26. Calvin Cycle/ Dark Reaction

27. Summary of Calvin cycle
In three turns of the Calvin cycle:
Carbon. 3CO2 combine with 3 RuBP acceptors,
making 6 molecules of glyceraldehyde-3-phosphate (G3P).
◦ 1 G3P molecule exits the cycle and goes towards making
glucose.
◦ 5 G3P molecules are recycled, regenerating 3 RuBP acceptor
molecules.
ATP. 9 ATP are converted to 9 ADP (6 during the fixation
step, 3 during the regeneration step).
NADPH. 6 NADPH are converted to 6 NADP+ (during the
reduction step).
A G3P molecule contains three fixed carbon atoms, so it takes two
G3Ps to build a six-carbon glucose molecule. It would take six
turns of the cycle, or 6 CO2, 18 ATP, and 12 NADPH, to produce
one molecule of glucose.

28. Kranz Anatomy Definition
Kranz anatomy is a unique structure observed in C4 plants. In
these plants, the mesophyll cells cluster around the bundle-sheath
cell in a wreath formation (Kranz means ‘wreath or ring). Also, the
number of chloroplasts observed in bundle sheath cells is more
than that in the mesophyll cell. This entire structure is densely
packed and plays a major role in C4 photosynthesis.
Advantage of Kranz Anatomy
We have established with the help of the above definitions that
Kranz Anatomy is a significant part of C4 plants. Thus, this has
several advantages to the respective plants. Some of those
advantages can be found below:
•It provides a perfect site for CO2 to be concentrated within the
plants, around the RuBisCO.
•It helps in preventing photorespiration
•It enables the carbon dioxide fixation twice within the C4 plants
with the help of the bundle sheath cells found in them

30. Cellular Respiration
Respiration: is a process in which organisms breathe
oxygen and excrete CO2 and water.
Aerobic respiration: when O2 is consumed as a reactant
along with organic fuel.
Anaerobic respiration: No O2 is used, other substances
are reactants that are harvesting chemical reaction.
Cellular respiration: includes both aerobic & anaerobic
processes where fuel breaks down by Mitochondria
generating ATP.
Organic compound+O2→CO2 +water + energy

31. Cellular respiration releases stored energy in glucose molecules and converts it into a form of energy
that can be used by cells.
Cellular respiration, the process by which organisms combine oxygen with foodstuff molecules,
diverting the chemical energy in these substances into life-sustaining activities and discarding, as waste
products, carbon dioxide and water. Organisms that do not depend on oxygen degrade foodstuffs in a
process called fermentation.
Cellular Respiration

32. The chemical elements essential to life are
recycled
 Photosynthesis generates
O2 and organic molecules
used by Mitochondria as
fuel for Cellular
respiration.
 The waste products of
cellular respiration are
CO2 and water which are
the raw materials for
Photosynthesis.

33. Structure
Mitochondria have an inner and outer membrane,
with an intermembrane space between them.
The outer membrane contains proteins known as
porins, which allow movement of ions into and out
of the mitochondrion. Enzymes involved in the
elongation of fatty acids can also be found on the
outer membrane.
The space within the inner membrane of the
mitochondrion is known as the matrix, which
contains the enzymes of the Krebs (TCA) and fatty
acid cycles, alongside DNA, RNA, ribosomes and
calcium granules.
The inner membrane contains a variety of
enzymes. It contains ATP synthase which generates
ATP in the matrix, and transport proteins that
regulate the movement of metabolites into and
out of the matrix.
The inner membrane is arranged into cristae in
order to increase the surface area available for
energy production via oxidative phosphorylation.

34. Stages of Cellular Respiration
1- Glycolysis
2- The Citric Acid
Cycle
3- Oxidative
Phosphorylation
(Electron
transport &
Chemiosmosis).
Figure 9.6; an overview of cellular
respiration. Page 166.

35. 1-Glycolysis
 Glycolysis: means Sugar splitting
 Glucose (6Carbon sugar) splits into two 3C sugars which are
oxidized and rearranged to form two molecules of Pyruvate.
The net energy produced by glycolysis is 2ATP and 2 NADH.
2-The Citric Acid Cycle
 Or Krebs Cycle: where Pyruvate enters the Mitochondria via
active transport, and converts to compound called Acetyl coA ,
which is the step junction between Glycolysis and Citric Cycle.
 Acetyl coA is broken down to 2 CO2 molecules;
 The cycle generates 1 ATP per turn, but most chemical energy is
transferred to NAD+ and FAD (vit Riboflavin) producing
3NADH and FADH.

36. 3-Oxidative Phosphorylation
 A- The electron transport chain: is a collection of molecules
embedded in the inner membrane of mitochondria during chain
electron carriers which alternate between reduced & oxidized states by
accepting & donating electrons. Electrons drop in free energy as they
go down the chain and are finally passed to O2, forming H2O.
 B- Chemiosmosis: a process in which energy stored in the form of
hydrogen ion across a membrane is used to drive cellular work, such as
the synthesis of ATP using enzyme ATP Synthase.
(ADP+Pi-----ATP synthase---→ATP)
 The net ATP produced are about 32-34 ATP.

37. Glycolysis is a sequence of 10 chemical reactions taking place in most cells that
breaks down a glucose molecule into two pyruvate (pyruvic acid) molecules.
Energy released during the breakdown of glucose and other organic fuel
molecules from carbohydrates, fats, and proteins during glycolysis is captured and
stored in ATP. In addition, the compound nicotinamide adenine dinucleotide
NAD+) is converted to NADH (during this step. Pyruvate molecules produced
during glycolysis then enter the mitochondria, where they are each converted
into a compound known as acetyl coenzyme A, which then enters the TCA cycle.
this metabolic pathway was discovered by three German biochemists-
Embden, Meyerhof, and Parnas in the early 19th century and is known
as the EMP pathway (Embden–Meyerhof–Parnas).
Stage 1
•A phosphate group is added to glucose in the cell cytoplasm, by the
action of enzyme hexokinase.
•In this, a phosphate group is transferred from ATP to glucose
forming glucose,6-phosphate.
Stage 2
Glucose-6-phosphate is isomerized into fructose,6-phosphate by the
enzyme phosphoglucoisomerase.
Stage 3
The other ATP molecule transfers a phosphate group to fructose 6-
phosphate and converts it into fructose 1,6-bisphosphate by the action
of the enzyme phosphofructokinase.
Stage 4
The enzyme aldolase converts fructose 1,6-bisphosphate into
glyceraldehyde 3-phosphate and dihydroxyacetone phosphate, which
are isomers of each other.

38. Step 5
Triose-phosphate isomerase converts dihydroxyacetone phosphate into glyceraldehyde 3-phosphate which is the substrate in the successive
step of glycolysis.
Step 6
This step undergoes two reactions:
•The enzyme transfers 1 hydrogen molecule from glyceraldehyde phosphate to nicotinamide adenine dinucleotide to form NADH + H+.
glyceraldehyde 3-phosphate dehydrogenase
• Glyceraldehyde 3-phosphate dehydrogenase adds a phosphate to the oxidized glyceraldehyde phosphate to form 1,3-bisphosphoglycerate.
Step 7
Phosphate is transferred from 1,3-bisphosphoglycerate to ADP to form ATP with the help of phosphoglycerokinase. Thus two molecules of
phosphoglycerate and ATP are obtained at the end of this reaction.
Step 8
The phosphate of both the phosphoglycerate molecules is relocated from the third to the second carbon to yield two molecules of 2-
phosphoglycerate by the enzyme phosphoglyceromutase.
Step 9
The enzyme enolase removes a water molecule from 2-phosphoglycerate to form phosphoenolpyruvate.
Step 10
A phosphate from phosphoenolpyruvate is transferred to ADP to form pyruvate and ATP by the action of pyruvate kinase. Two molecules of
pyruvate and ATP are obtained as the end products.
Key Points of Glycolysis
•It is the process in which a glucose molecule is broken down into two molecules of pyruvate.
•The process takes place in the cytoplasm of plant and animal cells.
•Six enzymes are involved in the process.
•The end products of the reaction include 2 pyruvate, 2 ATP and 2 NADH molecules.

40. Step 1. A carboxyl group is removed from pyruvate,
releasing a molecule of carbon dioxide into the
surrounding medium. The result of this step is a two-
carbon hydroxyethyl group bound to the enzyme (pyruvate
dehydrogenase). This is the first of the six carbons from
the original glucose molecule to be removed. This step
proceeds twice (remember: there are two pyruvate
molecules produced at the end of glycolysis) for every
molecule of glucose metabolized; thus, two of the six
carbons will have been removed at the end of both steps.
Step 2. NAD+ is reduced to NADH. The hydroxyethyl
group is oxidized to an acetyl group, and the electrons are
picked up by NAD+, forming NADH. The high-energy
electrons from NADH will be used later to generate ATP.
Step 3. An acetyl group is transferred to conenzyme
A, resulting in acetyl CoA. The enzyme-bound acetyl
group is transferred to CoA, producing a molecule of
acetyl CoA.
Note that during the second stage of glucose metabolism,
whenever a carbon atom is removed, it is bound to two
oxygen atoms, producing carbon dioxide, one of the major
end products of cellular respiration.

41. The TCA cycle (which is also known as the
Krebs, or citric acid, cycle) plays a central
role in the breakdown, or catabolism, of
organic fuel molecules. The cycle is made up
of eight steps catalyzed by eight different
enzymes that produce energy at several
different stages. Most of the energy
obtained from the TCA cycle, however, is
captured by the compounds NAD+ and flavin
adenine dinucleotide (FAD) and converted
later to ATP. The products of a single turn of
the TCA cycle consist of three
NAD+ molecules, which are reduced
(through the process of adding hydrogen,
H+) to the same number of NADH molecules,
and one FAD molecule, which is similarly
reduced to a single FADH2 molecule. These
molecules go on to fuel the third stage of
cellular respiration, whereas carbon dioxide,
which is also produced by the TCA cycle, is
released as a waste product.

42. KREBS CYCLE INTERMEDIATES
These intermediates are numbered on the diagram below
1.Citrate
2.Isocitrate
3.Oxoglutarate
4.Succinyl-CoA
5.Succinate
6.Fumarate
7.Malate
8.Oxaloacetate (oxaloacetic acid)
KREBS CYCLE STEPS
1.The TCA cycle begins with an enzymatic aldol addition reaction of acetyl CoA to oxaloacetate, forming citrate.
2.The citrate is isomerized by a dehydration-hydration sequence to yield (2R,3S)-isocitrate.
3.Further enzymatic oxidation and decarboxylation gives 2-ketoglutarate.
4.After another enzymatic decarboxylation and oxidation, 2-ketoglutarate is transformed into succinyl-CoA.
5.The hydrolysis of this metabolite to succinate is coupled to the phosphorylation of guanosine diphosphate (GDP)
to guanosine triphosphate (GTP).
6.Enzymatic desaturation by flavin adenine dinucleotide (FAD)-dependent succinate dehydrogenase yields
fumarate.
7.After stereospecific hydration, fumarate catalyzed by fumarase is transformed to L-malate.
8.The last step of NAD-coupled oxidation of L-malate to oxaloacetate is catalyzed by malate dehydrogenase and
closes the cycle.

43. KREBS CYCLE PRODUCTS
Before the Krebs cycle begins, a glucose molecule must
be converted to acetyl-CoA. This process yields 2 acetyl-
CoA molecules to be fed into the cycle. Thus, the cycle
proceeds twice per original glucose, yielding twice the
products shown below.
One TCA cycle "turn" yields 7 products:
•GTP
•3 NADH
•FADH2, which is converted to UQH2 in the presence of
coenzyme Q (ubiquinone)
•2 CO2 (carbon dioxide)
KEY TCA CYCLE ENZYMES
•Malic dehydrogenase
•α-Ketoglutarate dehydrogenase
•Citrate synthase
•Fumarase
•Aconitase
TCA CYCLE APPLICATIONS
These TCA-related metabolic applications are
commonly studied using stable isotope-labeled
compounds and mass spectrometry:
•Lipid Metabolism
•Amino Acid Metabolism
•Protein Metabolism (Turnover)
•Glucose Metabolism
•Energy Expenditure
•Metabolomics

44. ELECTRON TRANSPORT CHAIN
Electron Transport Chain is a series of compounds where it makes use
of electrons from electron carrier to develop a chemical gradient. It
could be used to power oxidative phosphorylation. The molecules
present in the chain comprises enzymes that are protein complex or
proteins, peptides and much more.
Large amounts of ATP could be produced through a highly efficient
method termed oxidative phosphorylation. ATP is a fundamental unit of
metabolic process. The electrons are transferred from electron donor
to the electron acceptor leading to the production of ATP. It is one of
the vital phases in the electron transport chain. Compared to any other
part of cellular respiration the large amount of ATP is produced in this
phase.
Q and Complex 2- Succinate-Q
reductase: FADH2 that is not passed through
complex 1 is received directly from complex 2.
The first and the second complexes are
connected to a third complex through
compound ubiquinone (Q). The Q molecule is
soluble in water and moves freely in the
hydrophobic core of the membrane. In this
phase, an electron is delivered directly to the
electron protein chain. The number of ATP
obtained at this stage is directly proportional
to the number of protons that are pumped
across the inner membrane of the
mitochondria.
Electron Transport Chain in Mitochondria
A complex could be defined as a structure that comprises a weak
protein, molecule or atom that is weakly connected to a protein. The
plasma membrane of prokaryotes comprises multi copies of the
electron transport chain.
Complex 1- NADH-Q oxidoreductase: It
comprises enzymes consisting of iron-sulfur and FMN. Here two
electrons are carried out to the first complex aboard NADH. FMN is
derived from vitamin B2.

45. Complex 3- Cytochrome c reductase: The third
complex is comprised of Fe-S protein, Cytochrome b,
and Cytochrome c proteins. Cytochrome proteins
consist of the heme group. Complex 3 is responsible
for pumping protons across the membrane. It also
passes electrons to the cytochrome c where it is
transported to the 4th complex of enzymes and
proteins. Here, Q is the electron donor and
Cytochrome C is the electron acceptor.
Complex 4- Cytochrome c oxidase: The 4th complex
is comprised of cytochrome c, a and a3. There are two
heme groups where each of them is present in
cytochromes c and a3. The cytochromes are
responsible for holding oxygen molecule between
copper and iron until the oxygen content is reduced
completely. In this phase, the reduced oxygen picks
two hydrogen ions from the surrounding

47. Figure 9.17 ATP yield per molecule of glucose at each stage of cellular respiration: Since
oxygen is required to complete the citric acid cycle and oxidative phosphorylation, these
two processes are known as aerobic respiration, and generate about 32-34 ATP per
glucose.

48. Fuels for cellular
respiration.
Carbohydrates, fats,
and proteins can all be
used as fuel for cellular
respiration.
Monomers of these
molecules enter
glycolysis or the citric
acid cycle at various
points.
Figure 9.20; the catabolism of
various molecules from food.

50. Fermentation and Anaerobic Respiration
A process where organic fuels are oxidized and generate
ATP without the use of oxygen.
Anaerobic respiration: has electron transport
chain, but the final electron acceptor is other than oxygen
→ it is sulfide.
Fermentation: the electrons from NADH are passed to
pyruvate, regenerating the NAD+ required to oxidize more
glucose.
Two types: Alcohol fermentation( yeast is used in baking)
& Lactic acid fermentation (Human muscles)

51. Types of Fermentation
There are three different types of fermentation:
Lactic Acid Fermentation
In this, starch or sugar is converted into lactic acid by yeast strains
and bacteria. During exercise, energy expenditure is faster than the
oxygen supplied to the muscle cells. This results in the formation of
lactic acid and painful muscles.
Alcohol Fermentation
Pyruvate, the end product of glycolysis is broken down into alcohol and
carbon dioxide. Wine and beer are produced by alcoholic fermentation.
Fermentation – Anaerobic Respiration
Anaerobic respiration is a type of cellular respiration where respiration takes place in the absence
of oxygen. Fermentation is an anaerobic pathway- a common pathway in the majority of
prokaryotes and unicellular eukaryotes. In this process, glucose is partially oxidised to form acids
and alcohol.
In organisms like yeast, the pyruvic acid formed by partial oxidation of glucose is converted to
ethanol and carbon dioxide (CO2). This anaerobic condition is called alcoholic or ethanol
fermentation. The whole reaction is catalyzed by the enzymes, pyruvic acid decarboxylase and
alcohol dehydrogenase. In certain bacteria and animal muscle cells, under anaerobic conditions, the
pyruvic acid is reduced to lactic acid by lactate dehydrogenase. This is called lactic acid
fermentation. The end products of these anaerobic pathways make them hazardous processes. For
example, a concentration of alcohol above 13 percent produced by yeast cells could kill themselves.
In the alcoholic and lactic acid fermentation, NADH+H+ is the reducing agent which is oxidized to
NAD+. The energy released in both the processes is not much and the total sum of ATP molecules
produced during fermentation is two, which is very less as compared to aerobic respiration.
However, this is commercially employed in the food and beverage industries, and pharmaceutical
industries.