Cellular Respiration
(Aerobic)
What is Cellular Respiration?
• The process of converting food energy into
ATP energy (catabolic route)
• C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + 36 ATP
Photosynthesis and Cell Respiration
are both important to Ecosystems
• Light is the ultimate
source of energy for all
ecosystems
• Chemicals are cycled and
Energy flows in one
direction
• Photosynthesis and
cellular respiration are
opposite reactions
Importance of Photosynthesis & Cell
Respiration to Ecosystems
• Light is the ultimate source of
energy for all ecosystems
• Chemicals are cycled and Energy
flows in one direction
• Photosynthesis and cellular
respiration are opposite reactions
Campbell Biology 10th Ed.
- Outer membrane:
* Has porin channels
Parts of a Mitochondrion * Freely permeable
to small molecules and ions
- Inner membrane:
* Impermeable to most
small molecules and
ions, including H+
* Contains respiratory e-
carriers (complexes I-
IV), ATP synthase (F0F1),
other membrane
transporters
- Matrix:
Contains enzymes
(pyruvate dehydrogenase,
citric acid cycle enzymes,
amino acid oxidation
enzymes), DNA,
ribosomes, ATP, ADP, Pi,
ions, soluble metabolic
intermediates
The sizes of fully sequenced plant mitochondrial genomes span over a 100‐fold range from
66 kb in Viscum scurruloideum to 11 000 kb in Silene conica.
In addition to the typical circular structure, some species of plants also possess linear, and
even multichromosomal architectures
Cellular Respiration is a Redox Reaction
(Oxidation)
• C6H12O6 + 6 O2 → 6 CO2 + 6 H2O
(Reduction)
• Glucose is oxidized when electrons and H+ are passed
to coenzymes NAD+ and FAD before reducing or
passing them to oxygen.
• Glucose is oxidized by a series of smaller steps so
that smaller packets of energy are released to make
ATP, rather than one large explosion of energy.
Why use ATP energy and not
energy from glucose?
• Breaking down glucose yields too much energy for
cellular reactions and most of the energy would be
wasted as heat.
• 1 Glucose = 686 kcal ATP4-
• 1 ATP = 7.3 kcal (30.5 kJ) Hydrolysis, with relief
• 1 Glucose → 36 ATP (~262 kcal)
of charge repulsion
ADP2-
Resonance
Ionization
stabilization
ADP3-
Resonance
hybrid
Chemical basis for ATP hydrolysis
Lehninger Principles of Biochemistry, 3rd ed.
ATP usually provides energy by group
transfers, not by simple hydrolysis
ATP hydrolysis in two steps:
the contribution of ATP to a reaction
is often shown as a single step (a),
but is almost always a two-step
process, such as that shown here for
the reaction catalyzed by ATP-
dependent glutamine synthetase:
Step 1: a phosphoryl group is first
transferred from ATP to glutamate,
Step 2: the phosphoryl group is
displaced by NH3 and released as Pi
Lehninger Principles of Biochemistry, 3rd ed.
Cellular Respiration can be divided into 4 Stages:
1) Glycolysis
2) Oxidation of Pyruvate / Transition Reaction
3) The Krebs Cycle
4) The Electron Transport Chain and
Chemiosmotic Phosphorylation
Where do the 4 parts of Cellular
Respiration take place?
• Glycolysis:
– Cytosol
• Oxidation of Pyruvate:
– Matrix
• The Krebs Cycle:
– Matrix
• Electron Transport
Chain and
Chemiosmotic
Phosphorylation:
– Cristae
Glycolysis
Glucose 2 Pyruvates
2 ATPs 4 ATPs (Net 2 ATPs)
2 NADHs
Glucose (C6) is split to make 2 Pyruvates (C3)
– 1st: ATP energy used to phosphorylate
glucose (stored energy)
– 2nd: phosphorylated glucose broken down into
two C3 sugar phosphates
– 3rd: the sugar phosphates are oxidized to yield
electrons and H+ ions which are donated to 2
NAD+ → 2 NADH (stored electron and
hydrogen for the Electron Transport Chain)
– 4th: The energy from oxidation is used to make
4 ATP molecules (net 2 ATP)
• This is substrate-level phosphorylation
because an enzyme transfers phosphate
from organic molecule to ADP for making
ATP
• Glycolysis produces very little ATP energy,
most energy is still stored in Pyruvate
molecules.
Oxidative Decarboxylation of Pyruvate
/Transition Reaction
2 Pyruvates 2 CO2
2 NADH
2 Acetyl CoA
• 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 NADHs carry electrons
and hydrogens to the
Electron Transport Chain.
Acetate
Pyruvate dehydrogenase complex (PDC)
• Cluster of 3 enzymes: pyruvate dehydrogenase
(E1), hidydrolipoyl transacetylase (E2), dihydrolipoyl
dehydrogenase (E3)
• 5 cofactors: thiamine pyrophosphate (TPP), FAD,
coenzyme A (CoA), NAD+ and lipoate
• Facilitates a series of chemical intermediates
remain bound to the surface of the enzyme
molecules as the substrate is transformed to
the final product
Oxidative decarboxylation of
pyruvate to acetyl-CoA by PDC
- 1: E1 catalyzes decarboxylation
- 2: transfer 2 electrons and the
acetyl group from TPP to E2
- 3: Acetyl CoA is yielded by E2
- 4: E3 promotes transfer of
hydrogen atoms to FAD of E3
- 5: the reduced FADH2 of E3
transfers a proton to NAD+,
forming NADH
Lehninger Principles of Biochemistry, 3rd ed.
The Krebs Cycle / Citric Acid Cycle
2 Acetyl CoA 4 CO2
2 ATP (substrate level phosphorylation)
6 NADH
2 FADH2
8 Enzymatic Steps in Matrix of Mitochondria:
The first step of the Krebs cycle combines
Oxaloacetate (4 C’s) with Acetyl CoA (2C) 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.
- The highlighted carbons are
those derived from acetate of
acetyl CoA
- In fumarate: can’t distinguish
the carbons originated from
acetyl CoA
NADH - Irrevisible reactions: 1, 3 and
FADH2 4
- Step 5: either ATP or GTP
produced, depending on which
succinyl-CoA synthetase
enzyme is the catalyst
Lehninger Principles of Biochemistry, 3rd ed.
The Electron Transport Chain
10 NADH 32 ATP
2 FADH2 H2O
Oxygen
• NADH and FADH2 produced earlier, go
to the ETC.
• NADH and FADH2 release electrons to
carriers/proteins embedded in the
membrane of the cristae.
• As the electrons are transferred, H+ ions
are pumped from the matrix to the
intermembrane space (up the
concentration gradient).
• Electrons are passed along a series of 9
carriers until they are ultimately donated
to an Oxygen molecule.
• ½ O2 + 2 electrons + 2 H+ (from NADH
and FADH2) → H2O.
http://vcell.ndsu.nodak.edu/animations/etc/movie.htm
Mobile
electron
carriers:
- Q: transfers
electrons to
complex III
- Cyt c:
transfers
electrons to
complex IV
Enzyme complex Prosthetic groups
I: NADH/ubiquinone oxidoreductase FMN, Fe-S
II: Succinate dehydrogenase FAD, Fe-S
III: Ubiquinone/cytochrome c oxidoreductase Heme, Fe-S
(cytochrome bc1 complex)
IV: Cytochrome oxidase Hemes, Cu A, CuB
Coenzymes serving as
universal electron carriers
• NAD+ (nicotinamide adenine dinucleotide),
NADP+, FMN (flavin mononucleotide) and FAD
(flavin adenine dinucleotide)
• Are water-soluble
• Nicotinamide nucleotides (i.e. NAD+ and NADP+)
move readily from one enzyme to another
• Flavin nucleotides (i.e. FMN and FAD) are usually
tightly bound to the enzymes (flavoproteins)
NAD+ + 2e- + 2H+ NADH + H+
NADP+ + 2e- + 2H+ NADPH + H+
(Oxidized form) (Reduced form)
OR
NAD+ + AH2 A + NADH + H+
A+ NADH + H+ NAD+ + AH2
(AH is reduced substrate and A is oxidized substrate)
2
Nicotinamide
(oxidized form)
Involved in activity of
oxidoreductase/dehydrogenase
enzymes (> 200 kinds)
Ex: Glucose 6-phosphate
Nicotinamide
dehydrogenase, glyceraldehyde (reduced form)
3- phosphate dehydrogenase,
lactate dehydrogenase, alcohol H H
dehydrogenase
- These coenzymes are
derived from vitamin
riboflavin
- Function in
flavoproteins: fatty acyl-
CoA dehydrogenase,
NADH dehydrogenase
(complex I), glycolate
dehydrogenase, etc.
2H+ + 2e-
- Can accept 2 protons
and 2 electrons (i.e.
fully reduced FADH2,
FMNH2).
- When accept only 1 H+
and 1 e-, called
semiquinone: a stable
free radical FADH. and
FMNH..
Proteins serving as universal
electron carriers
• Plastocyanine: water-soluble electron
carrier
• Ion-sulfur proteins and cytochromes: have
tightly bound prosthetic groups, water-
soluble or peripheral or integral
membranes proteins
Prosthetic group of
cytochromes
Isoprenoid tail
The cytochromes are proteins with
characteristic strong absorption of
visible light, due to their iron-
containing heme prosthetic group
The four nitrogen atoms are
coordinated with a central Fe ion.
Heme cofactors of a and b
cytochromes are tightly, but not
covalently bound to their
associated proteins
Heme C is covalently bound to the
protein through Cys residues
Fe-S centers of iron-sulfur proteins
2Fe-2S: include both
inorganic and Cys S
atoms
Single Fe ion
surrounded by the S
atoms of 4 Cys residues
In complex III, Fe-S
center is called
Rieske ion-sulfur
protein because one
Fe atom is
coordinated to 2 His
residues rather than
4Fe-4S 2 Cys residues
Lipophilic electron carriers
• Ubiquinone and Plastoquinone: lipid-
soluble quinones (thus work in non-
aqueous environment of membranes)
Ubiquinone
(Coenzyme Q; Q)
Accepts 2 electrons and 2 protons
3 types of electron transfer in
oxidative phosphorylation
• Direct transfer of electrons
e.g. Reduction of Fe3+ to Fe2+
• Transfer as a hydrogen atom (H+ + e-)
• Transfer as a hydride ion (:H-), which
bears 2 electrons
- Catalyzes the transfer
Positive side
of hydride ion from
NADH FMN Fe-S
centers (Fe-S, N-2 iron
sulfur proteins) - Q
- Also acting as
proton pump which is
driven by the energy of
electron transfer
- Ubiquinone in the
form of QH2 diffuses in
the mitochondrial inner
Negative side
membrane from complex
I to Complex III, where it
is oxidized to Q in a
process that also involves
outward movement of H+
NADH + 5H+ (N side) + Q NAD+ + QH2 + 4H+ (P side)
Another path of electrons to Q
In addition to Complex I,
Ubiquinone also receives e-
from Complex II (succinate
Fe-S centers via succinate
dehydrogenase)
- Complex II activities does
not add H+ to the
intermembrane space
https://www.youtube.com/watch?v=n3L7OY1TevU
NADH + 5H+ (N side) + Q NAD+ + QH2 + 4H+ (P side) (Complex I)
QH2 + 2 Cyt c1 (oxidized) + 2H+ (N side) Q + 2 Cyt c1 (reduced) + 4H+ (P side) (Complex III)
4 cyt c (reduced) + 8H+ (N side) + O2 4 cyt c (oxidized) + 4H+ (P side) + 2H2O (Complex IV)
4 2
4
Enzyme complex Prosthetic groups
I: NADH/ubiquinone oxidoreductase FMN, Fe-S
II: Succinate dehydrogenase FAD, Fe-S
III: Ubiquinone/cytochrome c oxidoreductase Heme, Fe-S
(cytochrome bc1 complex)
IV: Cytochrome oxidase Hemes, Cu A, CuB
Review ATP Production
1) Glycolysis → 2 ATP
2) Oxidation of Pyruvate → No ATP
3) The Krebs Cycle → 2 ATP
4) The Electron Transport Chain and
Chemiosmotic Phosphorylation:
– Each NADH produces 2-3 ATP so 10
NADH → 28 ATP
– Each FADH2 produces 2 ATP so 2
FADH2 → 4 ATP
Total = 36 ATPs
• 1 Glucose = 686 kcal
• 1 ATP = 7.3 kcal
• 1 Glucose → 36 ATP (~262 kcal)
• How efficient are cells at converting glucose
into ATP?
– 38% of the energy from glucose yields
ATP, therefore 62% wasted as heat (used
to maintain body temperature or is
dissipated)
– Ex. Most efficient Cars: only 25% of the
energy from gasoline is used to move the
car, 75% heat.
Krebs cycle in anabolism and
anaplerotic reactions replenishing
Krebs cycle intermediates
Lehninger Principles of Biochemistry, 3rd ed.
OXPHOS system =
oxidative phosphorylation
system, which includes
respiratory complexes I to
IV and ATP synthase
The Terrestrial Organic Carbon Cycle
Photosynthesis
CO2 + H2O CH2O + O2
Respiration and decay
• On land, production of organic carbon by photosynthesis
is largely balanced by respiration and decay
-- Respiration: Used by both plants and animals to
to produce energy for metabolism
-- Decay: Consumption of dead organic matter
by (aerobic or anaerobic) micro-
organisms
Organic and Inorganic Carbon
C is cycled between reduced and oxidized forms by natural processes
Organic carbon Inorganic carbon
(reduced) (oxidized)
‘CH2O’ CO2 carbon dioxide
H2CO3 carbonic acid
Example: HCO3 bicarbonate ion
Glucose -- C6H12O6 CO3= carbonate ion
Coal
Oil
ENNY HAGER/ THE IMAGE WORKS
http://www.nationalfuelgas.com
Organic
carbon
http://www.upl.cs.wisc.edu/~stroker/jungle.jpg
Inorganic
carbon
Seashells
http://www.cmas-md.org/Images/Sanjay/UnivTop4.jpg
Coral
http://www.summerclouds.com/Vero/Sea%20Shells.jpg http://educate.si.edu/lessons/currkits/ocean/
The Carbon Cycle
Atm Inorganic
Organic
C Cycle CO2 C Cycle
Carbon dioxide
Carbon compound in air
photosynthesis respiration
respiration
Carbon compounds in plants Carbon compounds in animals
Glucose eating Glucose
Starch cellulose Glycogen
Oils proteins Oils proteins
Carbon dioxide
Carbon compound in air
photosynthesis respiration
respiration
Carbon compounds in plants Carbon compounds in animals
Glucose eating Glucose
Starch cellulose Glycogen
Oils proteins Oils proteins
Death, decomposition
and excretion
Death and decomposition
Carbon compounds in decomposers
Glucose, proteins, oils, urea
Carbon dioxide
Carbon compound in air
photosynthesis respiration
respiration
Carbon compounds in plants Carbon compounds in animals
Glucose eating Glucose
Starch cellulose Glycogen
Oils proteins Oils proteins
Death, decomposition
Death and decomposition and excretion
Carbon compounds in decomposers
Glucose, proteins, oils, urea
respiration
Carbon dioxide
Carbon compound in air
photosynthesis respiration
respiration
Carbon compounds in plants Carbon compounds in animals
Glucose eating Glucose
Starch cellulose Glycogen
Oils proteins Oils proteins
Death, decomposition
Death and decomposition and excretion
Carbon compounds in decomposers
Glucose, proteins, oils, urea
respiration
Carbon dioxide
Carbon compound in air
photosynthesis respiration
respiration
Carbon compounds in plants Carbon compounds in animals
Glucose eating Glucose
Starch cellulose Glycogen
Oils proteins Oils proteins
Death, decomposition
Death and decomposition and excretion
Carbon compounds in decomposers
Death & fossilisation
Death & fossilisation Glucose, proteins, oils, urea
Carbon compounds in fossil fuels
Coal, oil, gas
respiration
combustion Carbon dioxide
Carbon compound in air
photosynthesis respiration
respiration
Carbon compounds in plants Carbon compounds in animals
Glucose eating Glucose
Starch cellulose Glycogen
Oils proteins Oils proteins
Death, decomposition
Death and decomposition and excretion
Carbon compounds in decomposers
Death & fossilisation
Death & fossilisation Glucose, proteins, oils, urea
Carbon compounds in fossil fuels
Coal, oil, gas
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