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CHAPTER 9
CELLULAR RESPIRATION
Breathing In
Mitochondria
Oxygen,
Glucose
Digestion of food
Carbondioxide,
Water
Breathing
Out/ Urine
C6H12O6
+
O2
CO2
+
H2O WHY?????
+ 36 ATP
Cell resp is so….. engaging even to
canines….if Buddy gets it - oh … so
will you!
Cellular respiration and photosynthesis
are opposite pathways (so .. ATP is
made during cell resp and used during
photosynthesi
Fig. 9.1
Gasoline Combustion
Cell Respiration
Organic compounds + O2 -> CO2 + H2O + Energy
Carbs, Protein, Lipids
C6H12O6 + 6O2 -> 6CO2 + 6H2O + Energy (ATP + heat)
ATP: Adenosine Triphosphate
• Couples cell resp. to Anabolic reactions
• Bonds between PO4 groups can be
broken to release energy (ADP/AMP is
made).
ATP: Adenosine Triphosphate
ATP: How it works…. review
• PO 4 released from
ATP is tagged to a
substrate that will
not normally react
• Substrate is
phosphorylated
and now able to
undergo the
chemical reaction
• *ATP can be
regenerated *
ATP Banks the Energy Released in Multiple Steps
From Glucose
CATABOLIC
PATHWAY
C6H12O6 + 6O2 -> 6CO2 + 6H2O
Chemistry basics for cell respiration
(NOT AGAIN!!)
Food has electrons
Electrons can be removed and moved
This releases ENERGY!
The loss of electrons is called oxidation
(also addition of O)
The addition of electrons is called reduction
(also addition of H)
 Redox reaction – involves oxidation + reduction
 Na + Cl -> Na+ + Cl• Na the electron donor, is the reducing agent and reduces
Cl.
• Cl the electron acceptor, is the oxidizing agent and
oxidizes Na.
 Redox reactions require both a donor and acceptor
 An electron looses energy as it shifts from a less
electronegative atom to a more electronegative one
 In the cell, electron moves from macromolecules (via
a H reservoir) to oxygen
Oxidized
C6H12O6 + 6O2 -> 6CO2 + 6H2O + Energy (ATP + heat)
Reduced
A redox reaction that relocates electrons closer to oxygen
releases chemical energy (ATP)
Electrons from glucose/food are carried by
NAD+ (high energy electron carrier)
1P
+2e-
2H (food) + NAD+ -> NADH + H+
Released in solution
+2H+
+2H+
+2e- Nicotinamide Adenine Dinucleotide
(NADH) – is the cells’ H reservoir
- Dehydrogenase - enzyme
Electrons “fall” from organic molecules to oxygen during
cellular respiration in a stepwise manner
Hydrogen atoms in Glucose give up these Electrons.
Energy is released at each step ….. as ATP
C6H12O6
Electron Transport Chain
G = -53Kcal/mole of NADH
Electrons are passed by increasingly electronegative
molecules in the chain until they are caught by oxygen.
Oxygen is the FINAL ELECTRON ACCEPTOR - why?
Oxygen isFig.the
9.5 most electronegative acceptor in the Electron Transport
Chain. It accepts the electrons (flowing from food) to make WATER
The Process of Aerobic Cellular Respiration
1. Respiration involves Glycolysis, the Krebs cycle and Electron Transport Chain
2. Glycolysis - breaks glucose (6Carbon) into two pyruvates (3Carbon). Packages
Hydrogen Electrons into NADH.
Glycolysis
Gain - 2 ATP + 2NADH
3. Shuttle - takes pyruvate from cytoplasm to mitochondria. Gain 2NADH.
4. Krebs cycle - takes the two 3 Carbon compounds from Glycolysis and extracts
all Carbons and Oxygens as CO2 and Hydrogen electrons are transported by
NADH/FADH2.
Gain - 2 ATP + 6NADH + 2FADH2
5. Electron Transport Chain and Oxidative Phosphorylation: Move electrons
through redox reactions, create a H+ (proton) gradient, and use the power of
proton gradient to make ATP
Gain - 10 NADH to 30 ATP and 2FADH2 to 4 ATP
Aerobic Cellular respiration generates 38 ATP molecules for each sugar molecule it
oxidizes. Shuttle may not be as efficient and produce less energy - so 36 ATP!
C6H12O6 + 6O2 -> 6CO2 + 6H2O + 38ATP
Energy flows from glucose -> NADH -> electron
transport chain -> proton-motive force -> ATP
Making ATP: Substrate level phosphorylation (ATP made from substrates) & Oxidative
Phosphorylation - (ATP made via Electon
transport Chain)
ATP
4 ATP in Substrate level
phosphorylation Vs 34 ATP
In Oxidative Phosphorylation
Shuttle
Fig. 9.6
2
2
34
1) Substrate-level
phosphorylation
(4/38 ATP)
• Here an enzyme
transfers a phosphate
group from an
organic molecule
(the substrate)
to ADP, forming
ATP.
Fig. 9.7
Remember that Electrons are REMOVED
from HYDROGEN and they are PASSED
DOWN the Electron Transport Chain along
Redox Reactions
What will be left if Electron is
Removed from a Hydrogen Atom
H+
(proton)
1P
Coupling of the redox reactions of the electron
transport chain to ATP synthesis is called chemiosmosis
Electron Transport Chain (ETC)
Does not make ATP!!
Chemiosmosis couples ETC to
Oxidative Phosphorylation
Electrons from NADH are removed
and H+ is released into
intermembrane space during ETC
+2e-
1P
2H (food) + NAD+ <- NADH + H+
+2H+
+2H+
+2e- Nicotinamide Adenine Dinucleotide
(NADH) – is the cells’ H reservoir
- Dehydrogenase - enzyme
2) Oxidative
Phosphorylation (90%
ATP – 34/38):
ATP synthase in the cristae
makes ATP from ADP and
Pi.
• ATPsynthase used the
energy of an existing proton
gradient to power ATP
synthesis. (H+ motive force)
• This proton gradient
develops between the
intermembrane space
and the matrix.
Fig. 9.14


Cytoplasm is Pyruvate)
What’s happening in different locations of the
Glycolysis
(End product
cell?
Shuttle - Cytoplasm into Mitochondria

Kreb’s Cycle - Matrix of Mitochondria
(fluid inside mitochondria)

Electron Transport Chain - Enzymes
located all along the inner
mitochondrial membrane; Electrons
ferried from NADH to Oxygen


ATP
H+ ions moved from Matrix to
Space between Inner and Outer
Membrane
Oxidative phosphorylation:

H+ ions move back into Matrix

ATP Synthase is in the Inner
Mitochondial Membrane (Cristae folds)

ATP is made in the Matrix
Fluid with Enzymes
For Glycolysis
Inter
Membrane
Space
Glycolysis
Krebs cycle
Cytoplasm
Mitochondrial
Matrix
No Oxygen
Needed
Needs Oxygen
Glycolysis
Krebs cycle
S- COA
C = O
2CO2
CH3
Input = Glucose, 2ATP
Input = Acetyl Co A
Output = 2 Pyruvate, 4ATP,
2NADH
Output = 4CO2, 6NADH,
2FADH2, 2ATP
Glycolysis
Fig. 9.8
Glycolysis
Fig. 9.9a
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Glycolysis
Fig. 9.9b
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Glycolysis
Shuttle
CO2
Krebs cycle
◊ The Krebs
cycle
consists of
eight steps
Fig. 9.11
◊ The Krebs
cycle
Fig. 9.12
◊ Electrons carried by
NADH are transferred to
the first molecule in the
electron transport chain,
flavoprotein (multiprotein
complex I).
• The electrons continue
along the chain which
includes several
cytochrome proteins
and one lipid carrier Ubiquinone
• The final electron
acceptor is: OXYGEN
because it is MOST
electronegative
• The product is WATER
and ……. (its not over)
ELECTRON TRANSPORT CHAIN
I
II
III
IV
Fig. 9.13
◊ Read this for Understanding:
◊ Electrons from NADH or FADH2
ultimately pass to oxygen.
• one O2 molecule is reduced to two molecules
of water.
◊ The electron transport chain generates
no ATP directly.
◊ Its function is to break the large free
energy drop from food to oxygen into a
series of smaller steps that release
energy in manageable amounts.
◊ The movement of electrons along the
electron transport chain does contribute
to chemiosmosis and ATP synthesis.
◊ A protein complex,
ATP synthase, in
the cristae actually
makes ATP from
ADP and Pi.
◊ ATP used the energy
of an existing proton
gradient to power
ATP synthesis.
• This proton gradient
develops between
the intermembrane
space and the
matrix.
Fig. 9.14
Fig. 9.15
◊ Chemiosmosis is an energy-coupling
mechanism that uses energy stored in the
form of an H+ gradient across a
membrane to drive cellular work.
• In the mitochondrion, chemiosmosis
generates ATP.
• Chemiosmosis in chloroplasts also generates
ATP, but light drives the electron flow down
an electron transport chain and H+ gradient
formation.
• Prokaryotes generate H+ gradients across
their plasma membrane.
◊ They can use this proton-motive force not only to
generate ATP but also to pump nutrients and waste
products across the membrane and to rotate their
flagella.
Fig. 9.16
◊ Fermentation: partial degradation of
sugars in the absence of oxygen
(Anaerobic)
◊ Cellular respiration: complete breakdwn
of sugars in the presence of oxygen
(Aerobic Respiration)
Fermentation
Cellular Respiration
Anaerobic (No O)
Aerobic (+ O)
Input: Glucose, Output: ATP
1st Process: Glycolysis
Electron Carrier: NAD+
Electron Acceptor:
Pyruvate/Acetaldehyde
Electron Acceptor:Oxygen
(Complete oxidation of food)
(incomplete oxidation of food)
Cytoplasm
Cytoplasm + Mitochondria
End products: ATP = 2, Lactic Acid
CH3CH2OHCOOH/Ethanol (C2H5OH)
ATP =36, CO2
and H20
Fermentation enables some cells to
produce ATP without the help of oxygen
 Anaerobic catabolism of sugars can occur by
fermentation.
 In alcohol fermentation, pyruvate is converted
to ethanol in two steps
◊ During lactic acid fermentation (muscle cells,
bacteria) pyruvate is reduced directly by NADH
to form lactate (ionized form of lactic acid).
◊ Some organisms (facultative anaerobes), including
yeast and many bacteria, muscle cells can survive
using either fermentation or respiration.
◊ Obligate anerobes = sorry, no choice have to be
anerobic!
◊ Pure aerobes = neuron/brain cell!
.
Feedback mechanisms control cellular respiration
◊ Supply and demand regulates it
◊ Allosteric regulation of phosphofructokinase
sets the pace of respiration.
• This enzyme is inhibited by ATP and stimulated
by AMP (derived from ADP).
◊ It responds to shifts in balance between production
and degradation of ATP: ATP <-> ADP + Pi <->
AMP + Pi.
• Thus, when ATP levels are high, inhibition of
this enzyme slows glycolysis.
• When ATP levels drop and ADP and AMP levels
rise, the enzyme is active again and glycolysis
speeds up.
◊ Citrate, the first product of the Krebs cycle,
is also an inhibitor of phosphofructokinase.
• This synchronizes the rate of glycolysis and the
Krebs cycle.
• Also, if intermediaries from the Krebs cycle are
diverted to other uses (e.g., amino acid
synthesis), glycolysis speeds up to replace
these molecules.
◊ Metabolic balance is augmented by the
control of other enzymes at other key
locations in glycolysis and the Krebs cycle.
◊ Cells are thrifty, expedient, and responsive
in their metabolism.