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CELLULAR RESPIRATION:
AEROBIC HARVESTING
OF CELLULAR ENERGY
© 2012 Pearson Education, Inc.
Introduction
In chemo heterotrophs, eukaryotes
perform cellular respiration
That harvests energy from food
which
yields large amounts of ATP, that
allows for cellular work.
© 2012 Pearson Education, Inc.
Photosynthesis and cellular respiration-the
circle of life’s energy!
To reduce entropy and perform work, life requires
energy.
In almost all ecosystems, energy ultimately comes
from the sun, which is why we studied
photosynthesis first!
Key to remember……
glucose and oxygen are produced, so that’s
what we have to work with!
© 2012 Pearson Education, Inc.
Ultimately, Cells tap energy from electrons
“falling” from organic fuels to oxygen
The energy necessary for life is contained in the arrangement of
electrons in chemical bonds in organic molecules.
An important question is how do cells extract this energy?
© 2012 Pearson Education, Inc.
Where
Have we
Seen something
Like this
Before??!!
Final metabolic pathway is the Electron Transport Chain
We can harvest electrons from atoms to control the proton
energy that follows them around.
Have to be VERY careful to control these ions or acids can
build up!
We can do this with a semi-permeable membrane, enzymes
to control (transport) the electrons and resulting protons
Final, stable electron and proton acceptors.
Figure 6.5C
Controlledrelease ofenergy forsynthesisof ATP
NADH
NAD
H
H O2
H2O
2
2
2
ATP
21
Semi-permeable membrane-crista
Enzymes-to control (transport) the electrons and
resulting protons –mobile enzymes: Cytochrome Q
and Cytochrome C
Non-mobile enzymes; NADH Reductase,
Ubiquinone, (Collectively called “complexes”) and
then ATP Synthase used to place electrons on their
final acceptor in a process called “chemiosmosis”.
Ultimately, Cells tap energy from electrons “falling” from organic fuels to oxygen
When the carbon-hydrogen bonds of organic compounds are broken,
electrons are created and then transferred to a “final electron/proton”
acceptor.
An electron loses potential energy when it “falls” to oxygen.
What will use all this harvested electron/proton energy as it “falls” to
create?
Think about what you know and come up with a substance who can
donate Hydrogen?
Think about what you know and come up with a substance who can
accept Hydrogen?
How is this done? By shuttling the electrons
and protons found in hydrogen!
Cellular respiration is the changes in hydrogen atom distribution.
Glucose
loses its hydrogen atoms and
becomes oxidized to CO2.
Oxygen
gains hydrogen atoms and
becomes reduced to H2O.
© 2012 Pearson Education, Inc.
STAGES OF CELLULAR
RESPIRATION
© 2012 Pearson Education, Inc.
Overview: Cellular respiration occurs in
four main stages
Cellular respiration consists of a sequence of steps that can
be divided into three stages.
Stage 1 – Glycolysis-Cytosol
Stage 2 – Pyruvate processing-Bridge between
cytosol and mitochondrion
Stage 3- Citric acid cycle-Mitochondrion
Stage 4 – Oxidative phosphorylation with
chemiosmosis- Cristae
© 2012 Pearson Education, Inc.
Cellular respiration
Stage 1: Glycolysis
occurs in the cytoplasm and is anaerobic, it
begins cellular respiration, and
breaks down glucose into two molecules of a three-
carbon compound called pyruvate/pyruvic acid
Goal, break sugar to collect hydrogens
Net versus Gross ATP gains
C6H12O6+ 4 ADP +4 Pi + 2 ATP + 2 NAD
2 C3H5O3+ 4ATP+ 2 NADH+ 2 ADP + 2 Pi
Pyruvate/Pyruvic Acid has lots more bond energy that can
be extracted!
We need to stabilize the citric acid and make it permeable to the outer
mitochondrial membrane.
This second stage of cell respiration is a “bridge reaction” because
Nothing is produced, but we get the task done!
The first substance encountered in the mitochondria by
The acetyl-Coa is oxaloacetate.
Together they form a stable 6 carbon compound called
“citrate/citric acid”
Hence the next main stage of cell respiration is called
The “Citric acid cycle”.
Stage 2: The citric acid cycle
takes place in mitochondria,
breaks pyruvate to carbon dioxide, and
supply the next stage with electrons (NAD/FAD)
recycle pyruvic acid/pyruvate stabilizer (Co-A)
regenerate Acetyl –CoA acceptor-oxaloacetate
Goal is to collect hydrogens, make some ATP
(substrate) and release waste
Fourth and final stage of Cellular
respiration
Stage 3: Oxidative phosphorylation
involves electrons carried by NADH and
FADH2,
They shuttle H e- to the electron transport chain
embedded in the inner mitochondrial
membrane, (cristae)
involves chemiosmosis which is passing H e-
and H+ through ATP synthase (chemiosmosis)
together, they generate ATP through oxidative
phosphorylation.
Figure 6.10_1
H
H
H
H
H
H
H
H
H
H
H
Oxidative Phosphorylation
Electron Transport Chain Chemiosmosis
I
II
IIIIV
NADH NAD 2 H
FADH2 FAD
O2 H2O
ADP P ATP
21
Electronflow
Proteincomplexof electroncarriers
Mobileelectroncarriers
ATPsynthase
Most ATP production occurs by oxidative
phosphorylation
Oxidative phosphorylation
involves electron transport and chemiosmosis and
requires an adequate supply of oxygen.
Electrons from NADH and FADH2 travel down the electron transport
chain to from one enzyme to another using mobile enzymes to assist in
the electron moving properly.
Finally, in chemiosmosis, ATP synthase channels the H e- and following
H+ to O2 waiting in the matrix.
© 2012 Pearson Education, Inc.
Figure 6.12
NADH
FADH2
NADH FADH2NADH
orNADH
Mitochondrion
CYTOPLASM
Electron shuttlesacross membrane
Glycolysis
Glucose2
Pyruvate
PyruvateOxidation2 Acetyl
CoA
Citric AcidCycle
OxidativePhosphorylation
(electron transportand chemiosmosis)
Maximumper glucose:
by substrate-levelphosphorylation
by substrate-levelphosphorylation
by oxidativephosphorylation
2
2
2
2
6 2
ATP 2 about
28 ATP AboutATP32
ATP 2
ALL ROADS!
CONNECTION: Interrupting cellular respiration
can have both harmful and beneficial
effects
Three categories of cellular poisons obstruct the process of oxidative
phosphorylation. These poisons
1. block the electron transport chain (for example, rotenone, cyanide, and
carbon monoxide),
2. inhibit ATP synthase (for example, the antibiotic oligomycin), or
3. make the membrane leaky to hydrogen ions (called uncouplers, examples
include dinitrophenol).
Figure 6.11
ATPsynthase
NADNADH
FADH2 FAD
H
H
H
H
H
H H H
2 H
H2O ADP ATPP
O221
Rotenone Cyanide,carbon monoxide
Oligomycin
DNP
But once we are past glycolysis, what is the major
reactant needed to complete the remaining steps of
cellular respiration?
HINT:
FERMENTATION: ANAEROBIC
HARVESTING OF ENERGY
© 2012 Pearson Education, Inc.
Fermentation enables cells to produce
ATP without oxygen
Fermentation is a way of harvesting chemical energy that does not require
oxygen. Fermentation
takes advantage of glycolysis,
produces two ATP molecules per glucose, and
reduces NAD+ to NADH.
The trick of fermentation is to provide an anaerobic path for recycling
NADH back to NAD+.
Then, since we can’t effectively catabolize pyruvates, the animal cell does
what it can and produces Lactic acid and CO2.
Fully anaerobic creatures like fungi, convert glucose to ethanol and CO2
Fermentation enables cells to produce
ATP without oxygen
Lactate is carried by the blood to the liver, where it is converted back to
pyruvate and oxidized in the mitochondria of liver cells.
The dairy industry uses lactic acid fermentation by bacteria to make
cheese and yogurt.
Other types of microbial fermentation turn
soybeans into soy sauce and
cabbage into sauerkraut.
Figure 6.13B
2 NAD
2 NADH
2 NAD
2 NADH
2 Ethanol
2 Pyruvate
Glucose
2 ADP
2 ATP
2 P
Gly
co
lys
is
2 CO2
Fermentation enables cells to produce
ATP without oxygen
Obligate anaerobes-archae bacteria
are poisoned by oxygen, requiring anaerobic conditions, and
live in stagnant ponds and deep soils.
Facultative anaerobes
include yeasts and many bacteria, and
can make ATP by fermentation
6.14 EVOLUTION CONNECTION: Glycolysis
evolved early in the history of life on
Earth Glycolysis is the universal energy-harvesting process of life.
The role of glycolysis in fermentation and respiration dates back to
life long before oxygen was present,
when only prokaryotes inhabited the Earth,
about 3.5 billion years ago.
© 2012 Pearson Education, Inc.
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