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Cellular Respiration
Pulling some things together…
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
What did the previous slide represent?
Notice that during each energy
transformation, heat is lost!
What is this called?
Combustion Reactions

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
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
A chemical reaction that involves a
hydrocarbon and oxygen. It produces
energy (heat) so rapidly that a flame
results.
The products of this reaction include
carbon dioxide and water.
C(x)H(x)+O2→H2O(g)+CO2(g)
Combustion is commonly called
burning.
It is an exothermic reaction.
Cells and Energy
Glycolysis and respiration as source of energy
for the cell
How do cells make ATP?
Chapter 6
Phosphorylation!
Cells need to generate ATP!

Substrate level
phosphorylation
 Uses enzymes
 Transfers phosphate
group from an organic
substrate to ADP.
 X-P + ADP + enzyme
X + ATP
Chemiosmotic Phosphorylation
a.k.a. Chemiosmosis



Needs a membrane.
Uses the potential
energy to create a
concentration
gradient of H+
(hydrogen ions) across
a membrane.
Uses special enzymes,
ATP synthases.
Things to keep in mind... (we are
going to go over this…)
Respiration = C6H12O6 + 6O2  6CO2 + 6H2O
• Exergonic or endergonic?
• What is oxidized?
• What is reduced?
• In what form is energy released?
• What is the importance of CO2 in the atmosphere?
• What is the source of oxygen in the atmosphere?
Reminder:


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Endergonic reactions:
have a net absorption
of E
Exergonic reactions:
have a net release of
E.
These reactions are
“coupled,” one does
not occur without the
other!


While cellular
respiration, in total,
is an exergonic
reaction, it is made
up of a series of
reactions which
involve both types!
C6H12O6 + 6O2 
6CO2 + 6H2O +
ENERGY RELEASED
(ATP)
Redox Reactions

The movement of electrons from one
molecule to another is an oxidationreduction reaction.


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
Loss of electrons is oxidation
Gain of electrons is reduction
LEO the lion goes GER
ex. C4H6O5 + NAD+  C4H4O5 + NADH + H+
oxidized
reduced
The “master” formula…
There are 2 types of cellular
respiration


With oxygen: aerobic
cellular respiration
(What are aerobic
exercises?)
Without oxygen:
anaerobic cellular
respiration a.k.a.
fermentation
Eukaryote vs Prokaryote
Glycolytic pathways
Overview of Cellular
Respiration
A. Glycolysis
(anaerobic)
Without oxygen
B. Fermentation
(anaerobic respiration)
With oxygen
B. Aerobic Respiration
1. Citric Acid Cycle
2. Electron Transport Chain
Would you like that with or
without oxygen?

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Aerobic - environments
with oxygen
Anaerobic - environments
without oxygen
Most organisms need O2
but there are some that
can live in either
environment and a few
that must live in the
absence of O2!
Saccharomyces cerevisiae
(yeast) images provided by Peter
Hollenhorst and Catherine Fox
Obligate Anaerobes


Clostridium botulinum - Grampositive, endospore-forming, rod
prokaryote. Vegetative and spore
stages. Note the flagella.
Causes botulism.
Magnification*: x2,000
Type: SEM


Clostridium tetani - Gram-positive,
rod prokaryote; vegetative and
spore stages. Note the flagella.
Causes tetanus. SEM
|Magnification*: x1,750
Type: SEM
Review of Mitochondria

Eukaryotic organisms
carry out cellular
respiration in the
mitochondria (power
house of the cell)
http://www.sci.sdsu.edu/TFr
ey/MitoMovies/CrisMitoMovi
e.htm
Reminder: Possible evolution of
mitochondria-endosymbiont
The Mitochondria


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Double membrane
Has it’s own DNA!!
Can reproduce in
cell…!
Endosymbiont??
Possible evolution?
http://hybridmedicalanimation.com/anim_mitosis_wmVideo.html
Introduction to Cellular Respiration

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The process by which food molecules
(glucose) are broken down to release
energy (ATP)
C6H12O6 + 6O2  6CO2 + 6H2O + Energy
In eukaryotic organisms, this process
takes place in the mitochondria. In
prokaryotic organisms, this process
takes place in the cell membrane.
Overview: Respiration occurs in
4 (5) main stages

Glycolysis
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Exergonic
Occurs in the cytoplasm
Splits glucose into 2 molecules of pyruvic acid
Pyruvic acid is modified into Acetyl CoA
as it diffuses into the mitochondria.

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Each pyruvic acid loses a carbon to CO2
This is a high energy fuel molecule for the
next stage

Krebs Cycle
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Exergonic
Occurs in the matrix of the mitochondria
Produces CO2 as a waste product
** Main function of first 2 stages: supply
3rd stage with electrons!
Electron Transport Chain and
Chemiosmotic Phosphorylation

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Occurs on the cristae of the mitochondria
Uses oxygen
Produces the most ATP
Overview of Aerobic Cellular
Respiration
Define the four stages of respiration and their location in
the cell
1
Glycolysis
Glucose
Pyruvate
2 ATP
2
Formation
of acetyl
coenzyme A
3
4
Citric
acid
cycle
Electron
transport
and
chemiosm
osis
Stage 1: Glycolysis
glyco- : sugar (glucose)
-lysis: to split
A. Glycolysis (Overview)


A molecule of glucose
(6 carbon compound)
is broken apart
making 2 pyruvic acid
compounds (3 carbons
each)
2 ATP and 2 NADH
molecules produced
Glycolysis

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STEP 1 - 2 phosphates are attached to glucose,
forming a new 6-C compound. The phosphate
groups come from 2 ATP, which are converted to
ADP. (Glucose is phosphorylated!)
STEP 2 - The 6-C compound formed in Step 1 is
split into 2 3-C molecules of PGAL.
STEP 3 - The 2 PGAL molecules are oxidized
(LEO), and each receives a phosphate group
forming 2 new 3-C compounds. The phosphate
groups are provided by 2 molecules of NAD+
forming NADH.
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STEP 4 - The phosphate
groups added in Step 1 and
Step 3 are removed from
the 3-C compounds.
This reaction produces 2
molecules of Pyruvic Acid.
Each phosphate group
combines with a molecule
of ADP to make a molecule
of ATP.
Because a total of 4
phosphate groups were
added, FOUR MOLECULES
OF ATP ARE PRODUCED.
Substrate-level phosphorylation

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Enzymes in the cytoplasm pass a high
energy phosphate to ADP to make ATP.
Not very efficient…
FYI: The high energy phosphates came
from the oxidation of BPG, in the
presence of an enzyme, forming PGAL
(a.k.a. G3P) and ATP.
Keep up with totals:
Summary
of
glycolysis:
Don’t panic… you do
not need to memorize
this, but it will give
you a greater
appreciation for what
really is happening to
get from glucose to
pyruvate!
How many different
enzymes are involved?
Question 1
How much ATP is needed to activate glycolysis?
Glucose
Energy investment phase and
splitting of glucose
2 ATP
3
steps
2 ADP
Fructose-1,6-bisphosphate
P
P
2 X Glyceraldehyde
phosphate (G3P)
P
P
(see next slide)
Question 2
How much ATP/net & ATP is produced in glycolysis?
2 X Glyceraldehyde
phosphate (G3P)
P
P
(G3P)
(G3P)
NAD+
NAD+
NADH
2 ADP
2 ATP
5 steps
Energy capture phase
NADH
2 ADP
2 ATP
Net yield per glucose:
Pyruvate Pyruvate
? ATPs and ? NADH
Question 3
Identify the exergonic and endergonic reactions in
the following exergonic coupled enzyme steps in
glycolysis:
Energy investment phase:
• Glucose + ATP  Glucose-6-phosphate + ADP
Energy capture phase:
• Phosphoenolpyruvate + ADP  Pyruvate + ATP
In summary….

2 ATP molecules were
used in Step 1, but 4
are produced in Step 4.
Therefore, glycolysis
has a NET YIELD of 2
ATP molecules for
every molecule of
glucose that is
converted into Pyruvic
Acid
http://biology.clc.uc.edu/course
s/bio104/atp.htm
Glucose
2 pyruvic
acid
molecules
+ 4 H+ + energy
stored in 2 ATP
molecules
Glycolysis Facts:
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Glycolysis is the universal E-harvesting
process of life.
Because glycolysis occurs universally, it
is thought to be an ancient metabolic
system.
The net gain of two ATP molecules
represents only 5% of the E that a cell
can harvest from a glucose molecule.
Pyruvic Acid’s 2 Possible Pathways

If O2 is not
available
 Fermentation
 alcoholic
 lactic acid
 many types of
fermentation!

If O2 is available
 Kreb cycle
2 Possible Paths if no O2 present
Why must pyruvate be converted to either ethyl alcohol or
lactate in the absence of oxygen?
Glycolysis
Glycolysis
Glucose (C6)
2
NAD+
Glucose
2 NADH
2 NAD+
2 NADH
2 ATP
2 ATP
2 Pyruvate (C3)
CO2
2 Ethyl alcohol (C2)
2 Pyruvate
2 Lactate (C3)
Stage 2: The Preparatory Reaction
Acetyl CoA Production
B.O.P. (Breakdown of Pyruvate)

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1. The 2 pyruvic acid compounds
(3C) are changed into 2 2-carbon
compounds and 2 molecules of CO2
2. Occurs in the space between the
membranes of the mitochondria
Takes place as pyruvate moves into
the matrix of the mitochondria
Production of Acetyl CoA


When pyruvic acid enters
the mitochondrial matrix,
it reacts with a molecule
called coenzyme A to form
Acetyl Coenzyme A,
abbreviated acetyl CoA.
CO2, NADH, and H+ are
produced in this reaction.
Remember: There are 2
pyruvic acids formed from
1 glucose!
Question 1
How many of the six carbons of glucose are lost in
this way?
Pyruvate (C3) + CoA + NAD+ 
Acetyl(C2)CoA + CO2 +NADH
Question 2
Considering the transition reaction and the first reaction
of the Krebs cycle below, how would you describe the role
of Coenzyme A?
Transition reaction:
Pyruvate (C3) + CoA  Acetyl(C2)CoA + CO2
Krebs cycle first reaction:
Oxaloacetate (C4)+ AcetylCoA  Citrate (C6) + CoA
Stage 3
Krebs Cycle a.k.a. Critic Acid Cycle
Krebs Cycle



Named for German-British
researcher Hans Krebs
(1900-1980).
Also called the Citric Acid
Cycle
The Krebs cycle is a
biochemical pathway that
breaks down Acetyl CoA,
producing CO2, H+, NADH,
FADH2, and ATP.
Step 1

A 2-Carbon
molecule of Acetyl
CoA combines with
a 4-Carbon
compound,
OXALOACETIC
ACID, to produce a
6-Carbon Compound
CITRIC ACID.
Step 2

Citric Acid releases a
CO2 molecule and a H
atom to form a 5Carbon compound. By
losing a H atom with its
electron , Citric Acid is
OXIDIZED. The H
atom is transferred to
NAD+, REDUCING it to
NADH.
Step 3

The 5-Carbon
compound releases a
CO2 molecule and a H
atom, forming a 4Carbon compound.
NAD+ is reduced to
NADH. A Molecule of
ATP is also synthesized
from ADP.
Step 4

The 4-Carbon compound
releases a H atom to form
another 4-Carbon
compound. The H atom is
used to reduce FAD (Flavin
Adenine Dinucleotide) to
FADH2, a molecule similar
to NAD+ that accepts
electrons during Redox
Reactions.
Step 5

The 4-Carbon
compound releases a
H atom to
regenerate
oxaloacetic acid,
which keeps the
Krebs cycle
operating. The H
atom reduces NAD+
to NADH.
Summary
Keeping up with totals:
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In Glycolysis 1 glucose molecule
produces 2 Pyruvic Acid molecules,
which can then form 2 molecules of
Acetyl CoA.
1 Glucose molecule causes 2 turns of the
Krebs cycle.
The 2 turns produce 6 NADH, 2 FADH2,
2 ATP, and 4 CO2 molecules.
The CO2 is a waste product that
diffuses out of the cells and is given off
by the organism.

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The bulk of the E released by the
oxidation of Glucose still has NOT been
transferred to ATP. Only 4 molecules of
ATP have been generated - 2 from
Glycolysis and 2 From the Krebs cycle.
10 molecules of NADH and the 2 FADH2
molecules from the Krebs cycle DRIVE
the next stage of Aerobic Respiration The Electron Transport Chain.
That is where MOST of the E transfer
from Glucose to ATP actually occurs.
Stages 4 and 5
Electron Transport Chain (ETC)
and Chemiosmosis
Electron Transport Chain


The electron transport
chain is a system of
electron carrying proteins
embedded into the inner
membrane of a
mitochondrion, the cristae.
These proteins transfer efrom one to another, down
the chain, much in the way a
bucket brigade passes
buckets of water.
Electron Transport Chain (ETC)


NADH is oxidized to NAD+ at the first
protein/enzyme complex. 2 H+ are moved
across the membrane and the high E
electron moves through a series of
membrane proteins.
As the e- pass through a second
protein/enzyme complex, its E is used to
move another 2 H+ across the membrane.
ETC con’t.



At protein/enzyme complex 3 another 2 H+
are moved across the membrane.
Once the e- has spent all of its E, it joins
oxygen and other H+’s and e- ‘s to make a
water molecule.
This process creates a gradient by using
the high energy e- and H from NADH (and
FADH2).
ETC and FADH2


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FADH2 can not enter the ETC at the same point. It
must enter at the 2nd protein/enzyme complex. Here
it is oxidized to FAD+. Since it only passes through 2
protein/enzyme complexes, it can only move 4 H+
across the membrane.
http://vcell.ndsu.nodak.edu/animations/etc/index.htm
Oxygen: the “ultimate” electron
acceptor!
Still no ATP!


The ATP is actually produced by a proton
motive force. This force is a store of
potential energy created by the gradient
formed when hydrogens (protons) are
moved across a biological membrane.
Therefore, the electron transport chain
merely produces a gradient through which
ATP can be made (this is known as
chemiosmosis).
2H+
2H+
2H+
2H+
2H+
e-
2H+
→ NAD+
Cytosol
Outer mitochondrial
membrane
Intermembrane
space
Inner
mitochondrial
membrane
Complex I
Complex III
Complex II
Complex IV
Matrix of
mitochondrion
Complex V:
ATP synthase
Chemiosmosis



A special protein called ATP synthase provides
a channel for H+ ions to move across the
cristae. It also contains the enzyme that
catalyzes the phosphorylation of ADP to from
ATP.
As H+ ions move through the port, their flow
drives the synthesis of ATP.
http://vcell.ndsu.nodak.edu/animations/atpgra
dient/index.htm
Summary
Websites with animations



http://www.science.smith.edu/departmen
ts/Biology/Bio231/etc.html
http://www.sp.uconn.edu/~terry/images/
anim/ETS.html
http://www.sci.uidaho.edu/bionet/biol115
/t4_energy/etc.htm
Total ATP generated:
Glycolysis
Glucose
2 ATP
Substrate-level
phosphorylation
2 ATP
4–6
ATP
2 Pyruvate
Transition
reaction
Substrate-level
phosphorylation
2 NADH
Citric
acid
cycle
Electron
transport and
chemiosmosis
2 NADH
6
ATP
6 NADH
18
ATP
2 FADH2
4
ATP
32 - 34
ATP
From the
scheme, what is
the function of
the electron
transport stage
of respiration?
Oxidative
phosphorylation
Total Energy Yield
Are carbs. our only option?
Other food…

Glucose is not the only material
that can be metabolized to
generate energy. Many
carbohydrates can be broken down
in glycolysis and enter the Krebs
Cycle. Proteins can be broken down
into amino acids and those can be
deaminated and the carbon chains
feed into the Krebs Cycle. The
very long carbon chains of fatty
acids can be chopped into two
carbon pieces by a process known
as Beta Oxidation. Since the fatty
acid chains can be up to 20 carbons
long there is a very great deal of
energy stored in fats.
Fermentation (a.k.a. anaerobic
respiration)
No oxygen required!
Anaerobic Respiration
In some organisms, there are
times when cells are without O2
for short periods of time. When
this happens, an anaerobic process
called fermentation follows
glycolysis and provides a means to
continue producing ATP until O2 is
available again.
Anaerobic Respiration



In the absence of O2, some cells can convert
Pyruvic Acid into other compounds through
additional biochemical pathways that also
occur in the cytosol.
The combination of Glycolysis PLUS these
additional pathways are known as
FERMENTATION.
During the processes of fermentation NO
ADDITIONAL ATP IS SYNTHESIZED.
2 Types of Fermentation

Lactic Acid
Fermentation
 occurs in some
bacteria, in
plants, and most
animals
(including
humans)

Alcoholic
Fermentation
 occurs in some
yeast and
bacteria
Lactic Acid Fermentation


Pyruvic acid is converted into lactic acid.
Lactic acid involves the transfer of 2 H
atoms from NADH and H+ to Pyruvic Acid. In
the process, NADH is oxidized to form
NAD+ which is needed to keep Glycolysis
operating.
Lactic Acid Fermentation
Bacteria can do it!

Lactic acid
fermentation by
microorganisms plays
an essential role in
the manufacture of
food products such
as yogurt and cheese.
So can you!



Certain animal cells, including our muscle cells
convert pyruvic acid to lactic acid.
During exercise, breathing cannot provide
your body with all the oxygen it needs for
aerobic respiration. When muscles run out of
O2, the cell switch to lactic acid
fermentation.
This process provides your muscles with the
energy then need during exercise.
Lactic Acid Fermentation


In L.A.F., the 2 molecules of pyruvic acid
formed from glycolysis are used to make
2 molecules of lactic acid and NAD+
which is necessary for glycolysis.
L.A.F allows glycolysis to happen
repeatedly for quick energy. Each time
glycolysis occurs, 2 ATP are formed.
Alcoholic Fermentation

In alcoholic fermentation,
pyruvic acid from glycolysis is
changed into ethyl alcohol and
CO2. As a result, NAD+ is
formed which is needed for
glycolysis. Each time glycolsysis
occurs, 2 ATP are made.
Alcoholic Fermentation
Alcoholic Fermentation cont.
This process is used in making
beer, wine, and bread.
 A.F. by the yeast in a bread
recipe produces CO2 bubbles that
raise the bread dough.
 Also, many bacteria carry out A.F.
under anaerobic conditions.

Fermentation
Let’s Compare Lactic Acid
Fermentation and Alcoholic
Fermentation...




Lactic Acid
Fermentation:
glucose
glycolysis (pyruvic
acid)
lactic acid + NAD+
+2 ATP




Alcoholic
Fermentation:
glucose
glycolysis (pyruvic
acid)
CO2 + ethyl alcohol +
2 ATP + NAD+
Fermentation Totals:
Comparison of energy from one
glucose molecule…
Lactic Acid Fermentation: 2ATP
 Alcoholic Fermentation: 2 ATP
 Cellular Respiration: 36 ATP
 Aerobic Respiration is more
energy efficient than anaerobic
respiration!

Let’s Compare Photosynthesis and
Cellular Respiration...

Photosynthesis:
 food accumulated
 energy from sun
stored in glucose
 CO2 taken in
 O2 given off
 needs sunlight
 occurs only in
presence of
chlorophyll

Cellular Respiration:
 food broken down
 energy in glucose
is released
 CO2 given off
 O2 taken in
 does not need
sunlight
 occurs in all living
cells