Cellular respiration is the process by which cells convert food energy from glucose into ATP energy through a series of metabolic pathways. It occurs in four main parts: glycolysis, oxidation of pyruvate, the Krebs cycle, and the electron transport chain and chemiosmotic phosphorylation. These pathways take place in the cytoplasm and mitochondria and ultimately produce 36-38 ATP per glucose molecule through substrate-level phosphorylation and chemiosmotic phosphorylation. Cellular respiration and its production of ATP are essential for powering cellular work and processes.

1. ZOOLOGYZOOLOGY
Cellular RespirationCellular Respiration
By-
Dr. Dinesh C. Sharma,
Head, Zoology
Govt. P. G. College, Noida

2. ZOOLOGY
What is Cellular Respiration?What is Cellular Respiration?
The process of converting food energyThe process of converting food energy
into ATP energyinto ATP energy
CC66HH1212OO66 + 6 O+ 6 O22 →→ 6 CO6 CO22 + 6 H+ 6 H22O + 36 ATPO + 36 ATP

3. ZOOLOGY
Why are both Photosynthesis and CellWhy are both Photosynthesis and Cell
Respiration important to Ecosystems?Respiration important to Ecosystems?
Light is the ultimateLight is the ultimate
source of energy for allsource of energy for all
ecosystemsecosystems
Chemicals cycle andChemicals cycle and
Energy flowsEnergy flows
Photosynthesis andPhotosynthesis and
cellular respiration arecellular respiration are
opposite reactionsopposite reactions

4. ZOOLOGY
Why do plants need bothWhy do plants need both
chloroplasts and mitochondria?chloroplasts and mitochondria?
Chloroplasts useChloroplasts use
energy from theenergy from the
sun to makesun to make
glucoseglucose
MitochondriaMitochondria
convert glucose toconvert glucose to
ATP—the energyATP—the energy
currency of the cellcurrency of the cell

5. ZOOLOGY
What is ATP?What is ATP?
Adenosine TriphosphateAdenosine Triphosphate
– 5-Carbon sugar (Ribose)5-Carbon sugar (Ribose)
– Nitrogenous baseNitrogenous base
(Adenine)(Adenine)
– 3 Phosphate groups3 Phosphate groups
Energy currency of theEnergy currency of the
cellcell
The chemical bonds thatThe chemical bonds that
link the phosphate groupslink the phosphate groups
together are high energytogether are high energy
bondsbonds
When a phosphate groupWhen a phosphate group
is removed to form ADPis removed to form ADP
and P, small packets ofand P, small packets of
energy are releasedenergy are released

6. ZOOLOGY
How is ATP used?How is ATP used?
As ATP is broken down, itAs ATP is broken down, it
gives off usable energy togives off usable energy to
power chemical work andpower chemical work and
gives off some nonusablegives off some nonusable
energy as heat.energy as heat.
Synthesizing molecules forSynthesizing molecules for
growth and reproductiongrowth and reproduction
Transport work – activeTransport work – active
transport, endocytosis, andtransport, endocytosis, and
exocytosisexocytosis
Mechanical work – muscleMechanical work – muscle
contraction, cilia and flagellacontraction, cilia and flagella
movement, organellemovement, organelle
movementmovement

7. ZOOLOGY
Why use ATP energy and notWhy use ATP energy and not
energy from glucose?energy from glucose?
Breaking down glucose yields too much energyBreaking down glucose yields too much energy
for cellular reactions and most of the energyfor cellular reactions and most of the energy
would be wasted as heat.would be wasted as heat.
1 Glucose = 686 kcal1 Glucose = 686 kcal
1 ATP = 7.3 kcal1 ATP = 7.3 kcal
1 Glucose1 Glucose →→ 36 ATP36 ATP
How efficient are cells at converting glucose intoHow efficient are cells at converting glucose into
ATP?ATP?
– 38% of the energy from glucose yields ATP,38% of the energy from glucose yields ATP,
therefore 62% wasted as heat.therefore 62% wasted as heat.

8. ZOOLOGY
Cellular Respiration is a Redox ReactionCellular Respiration is a Redox Reaction
CC66HH1212OO66 + 6 O+ 6 O22 → 6 CO→ 6 CO22 + 6 H+ 6 H22OO
OxidationOxidation is the loss of electrons or His the loss of electrons or H++
ReductionReduction is the gain of electrons or His the gain of electrons or H++
Glucose is oxidized when electrons and HGlucose is oxidized when electrons and H++
are passedare passed
to coenzymes NADto coenzymes NAD++
and FAD before reducing orand FAD before reducing or
passing them to oxygen.passing them to oxygen.
Glucose is oxidized by aGlucose is oxidized by a series of smaller stepsseries of smaller steps soso
that smaller packets of energy are released to makethat smaller packets of energy are released to make
(Oxidation)
(Reduction)

9. ZOOLOGY
Cell Respiration can be divided into 4 Parts:Cell Respiration can be divided into 4 Parts:
1) Glycolysis1) Glycolysis
2) Oxidation of Pyruvate / Transition Reaction2) Oxidation of Pyruvate / Transition Reaction
3) The Krebs Cycle3) The Krebs Cycle
4) The Electron Transport Chain and4) The Electron Transport Chain and
Chemiosmotic PhosphorylationChemiosmotic Phosphorylation

10. ZOOLOGY
Where do the 4 parts of CellularWhere do the 4 parts of Cellular
Respiration take place?Respiration take place?
Glycolysis:Glycolysis:
– CytosolCytosol
Oxidation ofOxidation of
Pyruvate:Pyruvate:
– MatrixMatrix
The Krebs Cycled:The Krebs Cycled:
– MatrixMatrix
Electron TransportElectron Transport
Chain andChain and
CheimiosmoticCheimiosmotic
Phosphorylation:Phosphorylation:
– CristaeCristae

11. ZOOLOGY
Parts of the MitochondriaParts of the Mitochondria

12. ZOOLOGY
Anaerobic Respiration (no oxygen required, cytoplasm)Anaerobic Respiration (no oxygen required, cytoplasm)
1. Glycolysis
(substrate level)
Glucose  2 Pyruvate
2 ATP 4 ATP (Net 2 ATP)
2 NADH
Aerobic Respiration (oxygen required, mitochondria)Aerobic Respiration (oxygen required, mitochondria)
2. Oxidation
of
Pyruvate
2 Pyruvate  2 CO2
2 NADH
2 Acetyl CoA
3. Krebs Cycle
(substrate level)
2 Acetyl CoA  4 CO2
2 ATP
6 NADH
2 FADH2
4. Electron
Transport
Chain
(chemiosmotic)
10 NADH  32 ATP
2 FADH2 H2O
Oxygen
Total: 36 ATP produced

13. ZOOLOGY
ATP is made in two ways:ATP is made in two ways:
1)1) Substrate LevelSubstrate Level
PhosphorylationPhosphorylation (glycolysis(glycolysis
& Krebs cycle)& Krebs cycle)
2)2) ChemiosmoticChemiosmotic
PhosphorylationPhosphorylation (electron(electron
transport chain)transport chain)
Substrate-LevelSubstrate-Level
Phosphorylation:Phosphorylation:
Energy and phosphate areEnergy and phosphate are
transferred to ADP using antransferred to ADP using an
enzyme, to form ATP.enzyme, to form ATP.
Phosphate comes from onePhosphate comes from one
of the intermediateof the intermediate
molecules produced frommolecules produced from
the breakdown of glucose.the breakdown of glucose.

14. ZOOLOGY
GlycolysisGlycolysis
Glucose (CGlucose (C66) is split to make) is split to make
2 Pyruvates (C2 Pyruvates (C33))
– 11stst
: ATP energy used to phosphorylate: ATP energy used to phosphorylate
glucose (stored energy)glucose (stored energy)
– 22ndnd
: phosphorylated glucose broken: phosphorylated glucose broken
down into two Cdown into two C33 sugar phosphatessugar phosphates
– 33rdrd
: the sugar phosphates are oxidized: the sugar phosphates are oxidized
to yield electrons and Hto yield electrons and H++
ions which areions which are
donated to 2 NADdonated to 2 NAD++
→→ 2 NADH (stored2 NADH (stored
electron and hydrogen for the Electronelectron and hydrogen for the Electron
Transport Chain)Transport Chain)
– 44thth
: The energy from oxidation is used to: The energy from oxidation is used to
make 4 ATP molecules (net 2 ATP)make 4 ATP molecules (net 2 ATP)
This is substrate level phosphorylationThis is substrate level phosphorylation
because an enzyme transfersbecause an enzyme transfers
phosphate to ADP making ATPphosphate to ADP making ATP
Glycolysis produces very little ATPGlycolysis produces very little ATP
energy, most energy is still stored inenergy, most energy is still stored in
Pyruvate molecules.Pyruvate molecules.
Glucose  2 Pyruvate
2 ATP 4 ATP (Net 2 ATP)
2 NADH

15. ZOOLOGY
Oxidation of Pyruvate /Transition ReactionOxidation of Pyruvate /Transition Reaction
When Oxygen is present,
2 Pyruvates go to the
matrix where they are
converted into 2 Acetyl
CoA (C2).
Multienzyme complex:
– 1st:
each Pyruvate releases
CO2 to form Acetate.
– 2nd:
Acetate is oxidized and
gives electrons and H+
ions
to 2 NAD+
→ 2 NADH.
– 3rd
Acetate is combined with
Coenzyme A to produce 2
Acetyl CoA molecules.
2 NADH’s carry electrons
and hydrogens to the
Electron Transport Chain.
2 Pyruvate  2 CO2
2 NADH
2 Acetyl CoA

16. ZOOLOGY
The Krebs Cycle / Citric Acid CycleThe Krebs Cycle / Citric Acid Cycle
8 Enzymatic Steps in Matrix of
Mitochondria: Break down and Oxidize
each Acetyl CoA (2-C’s) to release 2 CO2
and yield electrons and H+
ions to
3 NAD+
+ 1 FAD → 3 NADH + FADH2.
This yields energy to produce ATP by
substrate level phosphorylation.
The first step of the Krebs cycle combines
Oxaloacetate (4 C’s) with Acetyl CoA to
form Citric Acid, then the remaining 7
steps ultimately recycle oxalacetate.
Two Turns of the Krebs Cycle are required
to break down both Acetyl Coenzyme A
molecules.
The Krebs cycle produces some chemical
energy in the form of ATP but most of
the chemical energy is in the form of
NADH and FADH2 which then go on to
the Electron Transport Chain.
2 Acetyl CoA  4 CO2
2 ATP
6 NADH
2 FADH2

17. ZOOLOGY
The Electron Transport ChainThe Electron Transport Chain
NADH and FADHNADH and FADH22 producedproduced
earlier, go to the Electronearlier, go to the Electron
Transport Chain.Transport Chain.
NADH and FADHNADH and FADH22 releaserelease
electrons to carriers/proteinselectrons to carriers/proteins
embedded in the membraneembedded in the membrane
of the cristae. As theof the cristae. As the
electrons are transferred, Helectrons are transferred, H++
ions are pumped from theions are pumped from the
matrix to the intermembranematrix to the intermembrane
space up the concentrationspace up the concentration
gradient. Electrons aregradient. Electrons are
passed along a series of 9passed along a series of 9
carriers until they arecarriers until they are
ultimately donated to anultimately donated to an
Oxygen molecule.Oxygen molecule.
½ O½ O22 + 2 electrons + 2 H+ 2 electrons + 2 H++
(from NADH and FADH(from NADH and FADH22)) →→
HH22O.O.
10 NADH  32 ATP
2 FADH2 H2O
Oxygen
http://vcell.ndsu.nodak.edu/animations/etc/movie.htm

18. ZOOLOGY
Chemiosmotic PhosphorylationChemiosmotic Phosphorylation
Hydrogen ions travel down their concentration gradient through a channelHydrogen ions travel down their concentration gradient through a channel
protein coupled with an enzyme calledprotein coupled with an enzyme called ATP SynthaseATP Synthase..
As HAs H++
ions move into the matrix, energy is released and used to combineions move into the matrix, energy is released and used to combine
ADP + PADP + P →→ ATP.ATP.
Hydrogens are recycled and pumped back across the cristae using theHydrogens are recycled and pumped back across the cristae using the
Electron Transport Chain.Electron Transport Chain.
ATP diffuses out of the mitochondria through channel proteins to be usedATP diffuses out of the mitochondria through channel proteins to be used
by the cell.by the cell.
http://vcell.ndsu.nodak.edu/animations/atpgradient/movie.htm

19. ZOOLOGY
ATP SynthaseATP Synthase
Multisubunit complexMultisubunit complex
with 4 parts:with 4 parts:
– RotorRotor – spins as H– spins as H++
ions flowions flow
– StatorStator – holds the rotor and– holds the rotor and
knob complex together in theknob complex together in the
cristaecristae
– Internal RodInternal Rod – extends– extends
between rotor and knob, spinsbetween rotor and knob, spins
when rotor spins which thenwhen rotor spins which then
turns the knobturns the knob
– KnobKnob – contains 3 catalytic– contains 3 catalytic
sites that when turned changesites that when turned change
shape and activate the enzymeshape and activate the enzyme
used to make ATPused to make ATP

20. ZOOLOGY
Review ATP Production:Review ATP Production:
1) Glycolysis1) Glycolysis →→ 2 ATP2 ATP
2) Oxidation of Pyruvate2) Oxidation of Pyruvate →→ No ATPNo ATP
3) The Krebs Cycle3) The Krebs Cycle →→ 2 ATP2 ATP
4) The Electron Transport Chain and4) The Electron Transport Chain and
Chemiosmotic Phosphorylation:Chemiosmotic Phosphorylation:
– Each NADH produces 2-3 ATP soEach NADH produces 2-3 ATP so
10 NADH10 NADH →→ 28 ATP28 ATP
– Each FADHEach FADH22 produces 2 ATP so 2produces 2 ATP so 2
FADHFADH22 →→ 4 ATP4 ATP
Total = 36 ATPTotal = 36 ATP
1 Glucose = 686 kcal1 Glucose = 686 kcal
1 ATP = 7.3 kcal1 ATP = 7.3 kcal
1 Glucose1 Glucose →→ 36 ATP36 ATP
How efficient are cells at convertingHow efficient are cells at converting
glucose into ATP?glucose into ATP?
– 38% of the energy from glucose38% of the energy from glucose
yields ATP, therefore 62% wasted asyields ATP, therefore 62% wasted as
heat (used to maintain bodyheat (used to maintain body
temperature or is dissipated)temperature or is dissipated)
– Ex. Most efficient Cars: only 25% ofEx. Most efficient Cars: only 25% of
the energy from gasoline is used tothe energy from gasoline is used to
move the car, 75% heat.move the car, 75% heat.

21. ZOOLOGY
All Types of Molecules can be usedAll Types of Molecules can be used
to form ATP by Cell Respiration:to form ATP by Cell Respiration:
Proteins, Carbohydrates,Proteins, Carbohydrates,
and Lipids must first beand Lipids must first be
broken down into theirbroken down into their
monomers and absorbedmonomers and absorbed
in the small intestine.in the small intestine.
Monomers may beMonomers may be
further broken down intofurther broken down into
intermediate moleculesintermediate molecules
before entering differentbefore entering different
parts of Cell respirationparts of Cell respiration
to ultimately form ATP.to ultimately form ATP.

22. ZOOLOGY
Anaerobic Respiration: FermentationAnaerobic Respiration: Fermentation
If there is NO oxygen, then cells can make ATP byIf there is NO oxygen, then cells can make ATP by FermentationFermentation
Without oxygen, Oxidation of Pyruvate and the ElectronWithout oxygen, Oxidation of Pyruvate and the Electron
Transport Chain do not operate.Transport Chain do not operate.
GlucoseGlucose →→ PyruvatePyruvate →→ LactateLactate
NADNAD++
GlycolysisGlycolysis 2 NADH2 NADH Reduction RxnReduction Rxn oror
2 ATP2 ATP Alcohol + COAlcohol + CO22
Fermentation yields a net gain of 2 ATP by substrate level phosphorylationFermentation yields a net gain of 2 ATP by substrate level phosphorylation
for every 1 Glucose. (Inefficient)for every 1 Glucose. (Inefficient)
Two Forms of FermentationTwo Forms of Fermentation::
Lactic Acid Fermentation (animals)Lactic Acid Fermentation (animals)
Alcohol Fermentation (yeast)Alcohol Fermentation (yeast)