Download Cellular Respiration - Labs - Department of Plant Biology, Cornell

Clicker Question
Monosaccharide sugars and amino acids
first enter the blood stream at the:
A. capillaries in the small intestine
B. capillaries in the stomach
C. left atrium
D. right atrium
E. capillaries in the salivary glands
Where are we?
• Last time I discussed:
–
–
–
The circulatory system and the
transport of oxygen, glucose and other
nutrients throughout the body.
Heart attacks, strokes and pulmonary
embolisms.
The heart and lungs.
• Speaking of hearts and lungs,
–
We sang together (with Chloe): “How
do you measure, a year in the life?”
• Today we will cover:
–
Cellular respiration and the
biosynthesis of molecules.
With a Little Help from My Friends
• Take a couple minutes to meet
or get to know a little better
the people sitting around you.
• Make sure that nobody is left
out.
• Study through living. Study
nutrition, digestion, etc.
together over lunch or dinner!
Joe Cocker With a Little Help from My Friends Woodstock 1969
With a Little Help from My Friends with Clapton, Page and Beck
Town of Bethel, New York
Bethel Woods Center for the Arts
Cells Differ Because the Specifics of a Cell
Depend on Its Functional Specialization
• Each cell has the basic organelles
•
•
of a eukaryotic cell. However, the
proportion and position of each
organelle depends on the cell type.
Each cell has the basic chemicals
required for life, however, the
precursors required by each cell,
the rate of turnover of the
chemicals, and the chemicals
produced by each cell differ
depending on cell type.
The structure and chemical
composition of a cell depends on
the function of the cell in an
organ.
However Almost All Cells Require
Glucose and Oxygen to Make ATP
• Every cell “burns” glucose as an energy
•
•
source to synthesize ATP from ADP and
Pi.
Each cell also uses the carbon skeleton of
glucose to synthesize chemicals that are
necessary for that cell.
The majority of cells burn glucose
completely during cellular respiration.
– The complete combustion of glucose requires
oxygen. Aerobic respiration results in about
38 ATP/glucose.
– Some fast twitch muscle cells burn glucose
quickly but incompletely in the absence of
oxygen. This anaerobic respiration results
in only 2 ATP/glucose.
Figure 5.2B Aerobic Energy transformations in a
cell
Heat
Chemical reactions
From
the
aorta
Carbon dioxide
+
Glucose
+
ATP
ATP
water
Oxygen
Energy for cellular work
Burning: The combination of oxygen with a reduced carbon
source which yields carbon dioxide, water and heat.
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
Figure 6.2 We must breathe so that the cells of our
body get oxygen and eliminate carbon dioxide
O2
Breathing
CO2
Lungs
CO2
Bloodstream
O2
Muscle cells carrying out
Cellular Respiration
Glucose + O2
CO2 + H2O + ATP
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
First Law of Thermodynamics
• Energy cannot be
created or
destroyed.
• That is, our bodies
require energy for
the organs to do
their work and we
get that energy by
eating food.
We Need to Eat Approximately 1600
Calories/Day Just to Maintain the Body
Various activities
use up additional
Calories (=kcal).
McDonalds
Burger King
Wendy's
Putting the Number and Distribution
of Calories in Perspective
clintonbushhaitifund.org
www.redcross.org
www.unicef.org/
• If you eat a Quarter Pounder
with Cheese, a medium French
Fries and drink a medium
Classic Coke, you take in
1110 Calories.
• These are enough Calories to
allow you to run 7 minute
miles for about 1.4 hours.
• If you don’t run for 1.4 hours
(or do an equivalent amount
of work), you will store the
Calories as 123 g of fat (about
¼ of a pound) since fat has a
fuel value of 9 Calories/gram.
There Are Other Ways to Burn Calories
Fat is Good
• Fat is a very efficient
•
form of energy storage
since 1 gram of fat can
store 9 Calories, whereas
1 gram of carbohydrate
or 1 gram of protein can
only store 4 Calories.
If we stored energy as
carbohydrate or as
protein, we would weigh
more than we do.
Fat is a Light Way to Store Calories
• ~ 2000 Calories can be stored by ~½ pound of fat in our body.
– (2000 Calories) (1 g fat/9 Calories)(2.2 pounds/1000 g) = 0.49 pounds
of fat
• ~ 2000 Calories would be stored as ~ 1 pound of protein or ~
1 pound of carbohydrate in our body.
– (2000 Calories) (1 g protein or carbohydrate/4 Calories)(2.2
pounds/1000 g) = 1.1 pounds of protein or carbohydrate
Although Storing too Many Calories as Fat
(BMI >30) is Unhealthy
Skeletal Muscle Cells Burn (Oxidize) Calories
When We Do Work
• The food (glucose) is oxidized (loss of electrons and
•
•
their accompanying protons) by oxygen to form
carbon dioxide, water and available energy (ATP).
The oxygen is reduced (gain of electrons and their
accompanying protons) to form water.
The ATP formed is used for muscle contraction.
Food is Oxidized by a Class of
Enzymes Called Dehydrogenases
The dehydrogenases work by transferring the
electrons and their accompanying protons to NAD to
make NADH.
ATP is then Formed By a Controlled Oxidation of
NADH by an Electron Transport Chain
• The burning of wood
•
is an uncontrolled
release of energy in
the form of heat.
By passing electrons
stepwise though the
electron transport
chain, the energy of
NADH can be
conserved in ATP
molecules with a
minimal loss as heat.
The Controlled Burning of Food For Energy
Occurs in the Cytoplasm (Glycolysis) and
the Mitochondrion (Krebs Cycle and
Electron Transport Chain)
As the Electrons Travel from NADH to
Oxygen through Various Acceptors of the
Electron Transport Chain, They Pull Protons
Across a Membrane and Form an Electrical
Battery that can Make ATP
Respiratory Poisons, Including Cyanide and
Carbon Monoxide, Inhibit Electron Transport
and Prevent ATP Formation
The Carbohydrates, Fats and Proteins
Enter the Respiratory Pathway in
Various Places to Make ATP
This is a
miracle.
Imagine
a car
engine
that
could run
on gas,
butter,
peanuts
and hay.
Perhaps One Day a Car will be able to
Run on All Wastes
Many Molecules in Cells are Synthesized
from Intermediates Formed During
Respiration
• Some of the food
•
molecules are
incompletely oxidized
and are transformed
into other molecules.
The ATP is used to do
muscular work and
to put together carbon
skeletons in the
biosynthesis of
macromolecules.
The Discovery of Cellular
Respiration
• That is cellular
•
•
respiration and
biosynthesis in a
nutshell.
How were these
miraculous processes
discovered?
It all started with
Robert Boyle (1662)
and his vacuum
pump.
Robert Boyle Accidentally Discovered that Air Is
Necessary for Life
• Robert Boyle was conducting
•
•
experiments to see whether
butterflies could fly in air
made thin by his newly
invented vacuum pump.
When he pulled a vacuum in
the bell jar, in which they
were flying, the butterflies fell
down and died.
Did they die as a consequence
of the fall or did they become
weak because they needed
air?
Robert Boyle Accidentally Discovered
that Air Is Necessary for Life
• Boyle realized that the air
•
was necessary for life after
he repeated his experiments
using a lark with a broken
wing. Since the lark could
not fly, any adverse effects
of the lack of air on the lark
in the bell jar would not be
caused by falling but would
indicate the necessity of air
for life.
The lark died in the vacuum,
showing that air is
necessary for life.
Mice also Need Air to Live
• By putting a mouse in a
•
bell jar and removing
the air with a vacuum,
Boyle showed that air
was also a necessity for
mice.
But his critics
suggested that the
animals might have
died from being in an
uncomfortable place,
claustrophobia or the
lack of food.
Robert Boyle Performed Controls to
Convince Critics
In response to his critics, Boyle put a mouse in the
bell jar overnight, gave it a paper bed and plenty of
cheese and then placed the bell jar by the fireside to
keep the mouse warm during the night.
Robert Boyle Performs Controls to
Convince Critics
• In the morning, Boyle
observed that the mouse
was very much alive.
• However, as soon as Boyle
evacuated the air, the
mouse started to die,
showing that lack of air,
and not the lack of
“creature comforts” was
necessary for life.
Air is Taken Up By The Lungs
Robert Hooke (1726), an
assistant of Boyle’s and all
around genius, showed that
the air was taken up by the
lungs by demonstrating that a
dog whose diaphragm was
not working could be kept alive
if air was continuously blown
with a bellows through the
lungs, but not through other
parts of the body.
Oxygen is the Vital Part of the Air
• Joseph Priestley (1774) furthered the work of
•
Boyle and Hooke when he showed that animals
took up the part of the air that was necessary
for a candle to burn.
Thus oxygen was the vital part of the air
that was taken up by the respiration of animals.
Carl Djerassi and Roald Hoffmann
Antoine Lavoisier Showed that the Combustion of
Food during Respiration is Chemically Like the
Burning of Wood
• Also in the 1770s, Antoine
•
•
Lavoisier, the founder of
modern chemistry,
determined that
combustion results from
the combination of oxygen
with carbon and
hydrogen.
Lavoisier believed that
respiration and combustion
were analogous reactions.
Lavoisier used analogy to
discover new phenomena.
“In respiration, as in
combustion, it is the
atmospheric air which
furnished oxygen…; but since
in respiration it is…the blood,
which furnishes the combustion
matter, if animals did not
regularly replace by means of
food…that which they lose by
respiration, the lamp would
soon lack oil, and the animal
would perish as a lamp is
extinguished when it lacks
nourishment.”
“The proofs of this identity of effects in respiration
and combustion are immediately deducible from
experiment. Indeed, upon leaving the lung, the air
that has been used for respiration no longer contains
the same amount of oxygen; it contains not only
carbonic acid gas but also much more water than it
contained before it had been inspired.”
Formula for Combustion and Respiration
C(H2O) + O2  CO2 + H2O + heat
• Respiration was defined as a combustion
•
•
process and measured by the uptake of O2
and the expulsion of CO2 and H2O.
Using a melting ice calorimeter, Lavoisier
and Pierre Simon de Laplace found that for
equal outputs of CO2, approximately the
same amount of ice was melted by the
respiration of a guinea pig and the burning
of charcoal.
Lavoisier believed that the heat provided
the energy necessary for the processes we
associate with life.
Political Correctness and Science
• Like Priestley, Lavoisier
never finished his
experiments on
respiration because he
was “politically
incorrect”.
• Lavoisier, who was a
tax collector, lost his
head in a guillotine
during the French
Revolution.
Lectures on Respiration for Children
faraday
(Almost) All Cells Respire
• Scientists disagreed as to where the
conversion of O2 to CO2 took place.
Was it the lungs or was it the
blood?
• This was a false dichotomy. The
conversion occurred in both places,
as well as in (almost) every other
part of the organism, as Lazzaro
Measure oxygen uptake (↑)
Spallanzani (1803) showed when he or carbon dioxide evolution (↓).
isolated various tissues and
demonstrated that all tissues were
capable of consuming O2 and
giving off CO2.
The Crucial Secret…Respiration is a Cellular Process
Common to All Cells
Many biologists still did not believe
that respiration occurred outside the
blood. Eduard Pflüger (1872) removed
the blood of a frog and replaced it
with saline and found that this frog
respired just like a normal frog. He
also mentioned that insects and
plants that have no blood respire
too. Pflüger concluded, "Here lies,
and I want to state this once and for
all, the crucial secret of the regulation
of the total oxygen consumption by
the organism, a gravity which is
entirely determined by the cell
itself....“
The Scientific Method: A Critical
Attitude is Clearly Required…
According to Thomas Gold (1989),
“New ideas in science are not
always right just because they
are new. Nor are the old ideas
always wrong just because they
are old. A critical attitude is
clearly required of every
scientist….. Whenever the
established ideas are accepted
uncritically, but conflicting new
evidence is brushed aside and not
reported because it does not fit,
then that particular science is in
deep trouble—and it has
happened quite often in the
historical past.”
Be Aware of Cow Dung
Conventional
Wisdom
of
the
Dominant
Group
Always Be Skeptical: Even Babe Ruth Only
Got it Right at Bat 34% of the Time
Babe Ruth’s Lifetime Batting Average: 0.342
The Mitochondrion is the Organelle
Involved in Respiration
• By the end of the nineteenth
century, it became clear that
respiration was a cellular
process that took place in almost
•
•
each and every cell.
Soon after, centrifugation showed
that the uptake of oxygen was
associated with particles and
subsequent structural studies
showed that the mitochondrion
was the respiratory organelle.
Mitos is Greek for thread, and
chondrin is Greek for small grain.
The German Dye Industry
Mitochondria Can Be Stained With
Fabric Dyes
• At the suggestion of Paul Ehrlich,
•
Leonor Michaelis (1900) tested
the ability of the various newlyinvented fabric dyes to stain
living tissue.
Michaelis showed that the
mitochondria in pancreatic
exocrine cells could be selectively
and vitally stained with a dilute
solution of one of these dyes,
Janus green.
Staining is only transient because the mitochondria
reduce the dye and render it colorless. The ability of
mitochondria to oxidize and reduce various dyes was
what led Kingbury (1912) to propose that the
mitochondria may be involved in cellular respiration.
Glucose: A Condensation
of Six Formaldehydes (CH20)
The Discovery of Glycolysis
Glyco-lysis: the Breakdown of Sugar
Fermentation has been used as a Food Processing
Technique throughout the World to Preserve and Flavor
Food for Thousands of Years
•
•
•
•
•
•
•
•
•
•
Alcohol
Wine
Vinegar
Olives
Corned Beef
Bread
Sourdough
Sauerkraut
Natto
Soy Sauce
•Tea
•Sake
•Beer
•Cheese
•Pickles
•Kimchi
•Kefir
•Salami
•Prosciutto
•Yogurt
Louis Pasteur Guessed that Fermentation is
Respiration without Air, and it Required
Living Organisms
"I am of the opinion
that alcoholic
fermentation never
occurs without
simultaneous
organization,
development and
multiplication of cells....
If asked, in what
consists the chemical
act whereby the sugar is
decomposed ... I am
completely ignorant of
it."
Pasteur Had Trouble Convincing People that
Fermentation was a Complex Process
“Ah, you insist on thinking of alcoholic
fermentation as a simple breaking up of
sugar into alcohol and carbonic acid!
Undeceive yourselves…. Ah! So you are
bound to ignore the yeast in this
phenomenon, or at the most will
concede to it only the role of initiator!
Very well! Learn that this yeast always
borrows something from the sugar, and
makes a part of its own tissues out of
this food. Learn also that it is only on
the condition of keeping a little of the
sugar for itself, that it consents to give
you the rest in the form of alcohol.”
Louis Pasteur Did Not Get Everything
Right
• Whole yeast could
•
•
ferment a sugar
solution.
Louis Pasteur (1879)
tried but was unable
to get ground up yeast
to ferment a sugar
solution.
He declared that
fermentation was a
vital action that
required living cells.
Fermentation Can Occur in vitro
• Eduard Buchner (1897) using a
German beer yeast instead of a
French wine yeast was able to
obtain fermentation in vitro when
•
he added sugar to a yeast extract.
Actually this was a lucky find,
since Buchner had no interest in
glycolysis. He was making a
health tonic, and only added the
sugar as a preservative, when the
other antiseptics failed to keep
the extract sterile.
Origin of the Word: Enzyme
• Buchner named the
•
extract zymase, from
zyme, the Greek word
for yeast, and
diastasis, the Greek
word for break apart.
Willy Kühne named all
biocatalysts,
enzymes, from the
Greek words, en
zyme, which mean
“in yeast”.
Fermentation in Yeast Involves
Many Steps
• Unlike the burning of wood,
the cellular oxidation of
glucose that occurs at
ambient temperatures
•
depends on the intervention
of enzymes and takes
place in about a dozen
sequential steps.
This leads to the production
of many intermediates
and thus cellular respiration
is also known as
intermediary metabolism.
Fermentation and Glycolysis in Muscle
are Almost Identical Processes
It was astonishing for the
biochemists studying
fermentation in yeast
and bacteria or
glycolysis in muscle that
the chemistry of these
seemingly diverse
processes, which take
place in different
kingdoms, were almost
identical.
Discovering Biochemical Pathways
• The studies of glycolysis and
fermentation opened up an entirely
new way of doing chemistry. Prior
to these studies, chemicals were
isolated from cells but attempts to
define their relationship in the
cell were rebuked with the words,
“More matter with less art.”
• Feeling that it was time to say,
“Enough matter, more art”,
biochemists, including Arthur
Harden, Gustav Embden, Otto
Myerhof (1924) and Jacob Parnas
(1910) began to piece together the
biochemical pathways that
occur in living cells.
Elucidating a Biochemical Pathway
• How could they determine the
•
•
•
components and sequence of the
pathway in the days before
radioactive isotopes?
They found poisons that were
inhibitors of CO2 evolution.
Then they determined which
intermediates accumulated after
treatment with the inhibitor.
The chemical whose
concentration increased, after
treatment with an inhibitor, was
presumably the intermediate
produced just prior to the step
blocked by the inhibitor.
Elucidating a Biochemical Pathway
A→B→C→D→E→F→G
Which intermediate would build up first if I
added a chemical that inhibited the
enzyme that converts E to F?
Figure 6.7C Details of glycolysis
Steps 1– 3 A fuel molecule is
energized, using ATP.
PREPARATORY PHASE
Glucose
ATP
(energy investment)
Step
1
ADP
P
Glucose-6-phosphate
P
Fructose-6-phosphate
P
Fructose-1,6-diphosphate
2
ATP
3
ADP
P
Step 4 A six-carbon
intermediate splits into two threecarbon intermediates.
4
P
Step 5 A redox reaction
generates NADH.
+
P
5
NAD
P
NADH
Steps 6– 9 ATP and pyruvate
are produced.
+
5
NAD
+H+
Glyceraldehyde-3-phosphate
(G3P)
P
NADH
+H
P
ADP
ENERGY PAYOFF PHASE
P
+
P
P
1,3-Diphosphoglycerate
P
3-Phosphoglycerate
ADP
6
6
ATP
ATP
P
7
7
P
P
2-Phosphoglycerate
8
H2
O
8
H2
O
P
P
ADP
Phosphoenolpyruvate
(PEP)
ADP
9
ATP
9
ATP
Pyruvate
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
In the Absence of Oxygen, the NADH Must
Be Recycled or ATP Formation will not be
Sustainable
• In muscle, NADH is recycled to
•
NAD+ in the process of converting
pyruvic acid to lactic acid. The
net yield from the oxidation of
each glucose is 2 ATP.
In yeast, NADH is recycled to
NAD+ in the process of converting
pyruvic acid to ethanol. The net
yield from the oxidation of each
glucose is 2 ATP.
Anaerobic Respiration in Muscle and
Yeast
The Discovery of the Citric Acid
(Krebs) Cycle
Aerobic Glycolysis
In the presence of oxygen, glucose is eventually split
(lysed) into two pyruvic acids, which means that
only 2 out of 6 of the formaldehydes (HCOH) that
make up the glucose were oxidized during glycolysis.
Additional energy can be obtained by the
oxidation of pyruvic acid. But how?
How are the Pyruvic Acids Produced in Glycolysis
Burned to Produce Additional Energy?
After courageously escaping the Nazis with the help of
Albert Szent-Gyorgyi in 1933, Hans Krebs tackled the
problem of how pyruvate is oxidized to carbon dioxide
and water and was prepared to look for a cycle.
Cycles (in Life and Biology) Facilitate
Regulation and Integration
• While he was in
•
Germany, Hans Krebs
had determined that in
the liver, urea is
synthesized from
carbon dioxide and
ammonia in a cyclic,
not a linear reaction.
Compared with a linear
pathway, a cycle
allows better
regulation and
integration with the
whole cell.
Krebs Showed Pyruvic Acid Was “Burned” in
a Cycle Too
• Krebs found that a
•
number of organic acids,
including citric acid
stimulated O2 uptake in
muscle and liver.
He also found that in the
presence of NAD tiny
(catalytic) amounts of
these organic acids
stimulated the oxidation
of large quantities of
pyruvic acid.
Pyruvic acid
Krebs Showed Pyruvic Acid Was “Burned” in
a Cycle
• The presence of
•
malonate, an inhibitor
of succinic acid
oxidation, results in the
build up of succinic acid
no matter which
intermediate is added.
These data indicated
that the intermediates
are arranged in a
cycle.
Krebs Showed Pyruvic Acid Was “Burned” in
a Cycle
• The presence of
•
malonate, an inhibitor
of succinic acid
oxidation, results in the
build up of succinic acid
no matter which
intermediate is added.
These data indicated
that the intermediates
are arranged in a
cycle.
The Establishment Usually Takes Time to
Recognize the Work of a Prepared Mind
• When Krebs first submitted his paper to the “premier journal”
Nature, he got the following rejection letter:
"The editor of NATURE presents his compliments to Dr.
H. A. Krebs and regrets that as he has already sufficient
letters to fill the correspondence column of NATURE for
seven or eight weeks, it is undesirable to accept further
letters at the present time…."
• Krebs then submitted his paper to the “second class journal”
Enzymologia where it was accepted in 1937 and in 1953 Krebs
won the Nobel Prize in Physiology of Medicine for his work.
nobelprize.org
Hans Krebs on His Cycle
Vitamins B1- and B3-dependent
conversion of pyruvic acid to acetyl
CoA
A biochemical lesion results because the above step does not
occur when Vitamins B1 or B3 are missing.
Nutrition: The B vitamins are
Necessary for Energy Metabolism
• Every cell requires Niacin (vitamin B3),
•
•
which is an essential component of NAD,
a cofactor in anaerobic and aerobic
energy metabolism.
Cells that use aerobic energy metabolism
also require Thiamine (vitamin B1),
which is an essential part of a coenzyme
required for aerobic energy metabolism.
Some cells are more sensitive to a
deficiency in a given nutrient than
others, which is why diseases caused by
nutrient deficiencies show up in a
particular organ, tissue or cell type.
Beriberi (Paralysis Due to Damaged
Nerves) and Pellagra (4Ds: Dermatitis,
Diarrhea, Dementia, and Early Death)
Biochemical Lesion: Nature and Nurture
• Pyruvic acid must be activated before it
•
•
can enter the Krebs cycle.
The enzyme that catalyzes this activation
step requires thiamin pyrophosphate
(TPP), a coenzyme derived from vitamin
B1.
A deficiency in vitamin B1 results in an
“environmentally-induced” “biochemical
lesion”, a term coined by Rudolph
Peters ().
• The inability to perform a certain step in a
pathway may also be due to a deficiency in
an enzyme involved in catalyzing that step.
According to Archibald Garrod (), this
may be due to an inborn error in
metabolism, i.e. a genetic lesion.
The Discovery of the Electron
Transport Chain and Oxidative
Phosphorylation
The NADH Produced By the Krebs Cycle
Must Be Oxidized
• The Krebs cycle itself does not require
•
•
•
oxygen nor generate much energy in the
form of ATP since the NADH contains
much of the original energy of the glucose
molecule.
The NADH must be oxidized by the
electron transport chain.
At body temperature, oxygen does not
directly attack NADH so how does the
oxygen act?
It seemed likely that the catalyst would
contain iron, which has a high affinity for
oxygen, and is able to bind it reversibly.
Think of rust, which is iron oxide.
Discovery of the Electron Transport Chain
• In the mid 1800’s it was widely held
•
that the blood was involved in
respiration and indeed an ironcontaining compound was present in
the blood and is called hemoglobin.
The concentration of iron in the blood is
so high that the French nobility wore
rings made from the iron extracted from
the blood of their friends as a keepsake
much like people wear a lock of a loved
one’s hair in a ring around their finger
or in a locket around their neck.
Discovery of the Electron Transport
Chain
• In the 1850's Claude Bernard
•
•
realized that the color of the
blood depended on its state
of oxygenation.
George Gabriel Stokes (1864)
concluded that hemoglobin
exists in oxidized (bright
reddish) and reduced states
(muddy dark red), and these
can be distinguished by their
absorption spectra.
A blood oxygen meter
measures the color of blood.
Oxygenated Blood Reflects Bright Red.
Deoxygenated and Carbonmonoxide-containing Blood
Reflects Blue and Red and Looks Dark Purplish.
• Deoxygenated- and
•
•
carbonmonoxy-hemoglobin absorb
less and reflect more blue (400500 nm) and thus appears bluer
than oxygenated hemoglobin.
Deoxygenated- and
carbonmonoxy- hemoglobin
absorb more red (600-650 nm)
and reflect less red which makes
it appear less red than oxygenated
hemoglobin.
The bright blue color of the veins
depends on the optical
properties of the skin as well as
the purplish color of the blood
within them.
Blue
Green
Red
Discovery of Cytochromes
• After the general acceptance that
respiration was a cellular phenomenon
and not one that occurred only in the
blood, Charles MacMumm (1886)
searched for respiratory pigments in
many animal tissues.
• He found a pigment whose
absorption spectrum varied with its
oxidation state—just like hemoglobin.
• David Keilin (1925) showed that this
pigment was really a mixture of 3
pigments which he named cytochromes
a, b and c. Cytochrome means “cell
color”.
• But none of these cytochromes
interacted directly with O2.
The Discovery of the Iron-Containing
Enzyme (Cytochrome Oxidase) that
Binds Oxygen
• Otto Warburg, Hans Krebs’
•
teacher and a Jew who
accepted Hitler’s invitation
to stay in Germany as an
honorary Aryan, discovered
another cytochrome, called
cytochrome oxidase that
directly binds O2.
Carbon monoxide and
cyanide cause death by
inhibiting the action of this
protein.
Discovery that the Mitochondrial
Electron Transport Chain Converts the
Energy in NADH into the Energy in ATP
• Albert Lehninger showed
•
that ATP is formed when
NADH is given to isolated
mitochondria.
The complete combustion of
glucose in the presence of
O2 yields approximately 38
ATPs (compared to 2 ATPs
obtained by glycolysis in the
absence of oxygen).
Figure 6.10 Oxidative phosphorylation, using electron
transport and chemiosmosis in the mitochondrion
H+
Intermembrane
space
.
H+
H+
H
H+
Protein
complex
H+
+
H+
H+
H+
Electron
carrier
ATP
synthase
Inner
mitochondrial
membrane
FADH2
Electron
flow
NAD+
NADH
Mitochondrial
matrix
FAD
H+
1
O 2 + 2 H+
2
H+
H+
H2O
Electron Transport Chain
OXIDATIVE PHOSPHORYLATION
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
ADP +
ATP
P
H
+
Chemiosmosis
A Summary of Cellular Respiration
ATP is Used as an Energy Source
for:
•
•
•
•
•
•
Synthesizing carbohydrates (dehydrations)
Synthesizing DNA and RNA (dehydrations)
Synthesizing proteins (dehydrations)
Synthesizing lipids (dehydrations)
Synthesizing coenzymes (e.g. NAD)
Transporting substances across
membranes
• Secretion
• Cell motility: muscle movement
• Nearly everything…
Figure 6.3 Summary equation for cellular respiration
C6H12O6
Glucose
+
6
O2
Oxygen gas
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
6
CO2
Carbon
dioxide
+
6
H2O
Water
+
ATPs
Energy
When you eat and breathe, you make cellular
respiration possible.
O2
Breathing
CO2
Lungs
CO2
Bloodstream
O2
Muscle cells carrying out
Cellular Respiration
Glucose + O2
CO2 + H2O + ATP
Science Songs
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings