CHAPTER 9 – CELLULAR RESPIRATION
Cellular Respiration →
breaking down food to
get ATP
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MITOCHONDRIA
POWERHOUSE OF THE CELL!!
The mitochondria is the organelle
responsible for cellular respiration. The
Krebs cycle and also the ETC take place
here to produce ATP. It is a double
membrane with the inner membrane highly
folded (to increase surface area and make
the mitochondria more efficient.
Intermembrane
Space
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Organic compounds possess
potential energy as a result of
the arrangement of electrons
in the bonds between their
atoms.
Enzymes catalyze the
systematic degradation of
organic molecules that are rich
in energy. Some of the
released energy is used to do
work; the rest is dissipated as
heat.
Fermentation, leads to the
breakdown of sugars without
the use of oxygen (anaerobic.)
A more efficient catabolic
process, aerobic respiration,
consumes oxygen as a
reactant.
Although cellular respiration
technically includes both
aerobic and anaerobic
processes, the term is
commonly used to refer only to
the aerobic process.
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CELLULAR RESPIRATION – BACKGROUND INFO
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Carbohydrates, fats, and proteins can all be used as the fuel, but
it is most useful to consider glucose:
Equation C6H12O6 + 6O2  6CO2 + 6H2O + energy (ATP + heat)
The catabolism of glucose is exergonic, with G = −686 kcal per
mole of glucose.
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OXIDATION AND REDUCTION
In Cellular
Respiration,
is
and
is
Note: Look at the proximity of the electrons; they lose
potential energy as they get closer to the electronegative
atoms.
.
Reducing agent =
the thing that gets
oxidized (glucose!)
Oxidizing agent = the
thing that gets
reduced (oxygen!)
Reduction – Gaining an electron; becomes more negative (hint: usually it gains a
H+ too to keep it neutral – so look for the one that got a hydrogen added to it)
Oxidation – Loses an electron; becomes more positive
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ELECTRONS “FALL” CLOSER TO OXYGEN USING
THE ETC AND NADH
NADH = nicotinamide adenine
dinucleotide (nicotinamide is
a nitrogen base that is NOT
found in DNA or RNA)
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NADH shuttles electrons from the
food to the ETC
Glucose → NADH → ETC → Oxygen
NAD+ = oxidized form
NADH = reduced form (note the H
on the end!)
Controlled release
of energy in steps
via the ELECTRON
TRANSPORT CHAIN
(ETC)!
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GENERAL OVERVIEW – CELLULAR RESPIRATION
Glycolysis → in cytosol;
turns glucose to 2
pyruvate, net gain of 2
ATP and 2 NADH;
anaerobic
Krebs (Citric Acid Cycle)
→ in mitochondrial
matrix; 1 glucose powers
2 turns of Krebs, makes
little ATP, NADH, and
FADH2 (electron taxis);
passes e- to ETC
Intermediate Step  Pyruvate gets transported into the
mitochondria and gets converted into Acetyl-CoA, thereby losing
a Carbon and releasing CO2 during this step; Acetyl CoA enters
the Krebs
ETC → uses oxidative
phosphorylation
(concentration gradients
and chemiosmosis) to
make lots of ATP
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OXIDATIVE PHOSPHORYLATION VS. SUBSTRATE
LEVEL PHOSPHORYLATION
Substrate Level Phosphorylation
→ when the P from one
molecule gets attached to ADP to
make ATP; it gets directly added
on; ATP is made this way in
glycolysis and the Krebs
Oxidative Phosphorylation → uses a concentration
gradient to power chemiosmosis; 90% of the ATP is
made this way; very efficient; used in the ETC
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GLYCOLYSIS
Main Goal of Glycolysis is to turn
glucose into two pyruvate:
- Series of 10 steps  Two phases:
Energy Investment and Energy
Payoff
- Produces a net gain of 2 ATP and
2 NADH (e- carriers)
- From here it can go to the
Krebs cycle (aerobic respiration)
or to Fermentation (anaerobic)
- Does NOT release any 02
- Occurs in the cytosol
Overall: Glucose → 2 Pyruvate; net
gain 2 ATP and 2 NADH
Glycolysis is ANAEROBIC….does NOT require oxygen!!
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GLYCOLYSIS – ENERGY INVESTMENT PHASE
In the energy investment phase, 2
ATP are put into the process.
Glucose → Glucose – 6 – phosphate → Fructose-6phosphate → Fructose- 1, 6 – biphosphate → G3P
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GLYCOLYSIS – ENERGY PAYOFF PHASE
In the energy payoff
phase, 4 ATP are
produced (net gain of
2) and 2 NADH are
made (to be shipped to
the ETC).
G3P → 1, 3 – biphosphoglycerate → 3-phosphogylcerate → 2phosphoglycerate → Phosphoenolpyruvate → Pyruvate
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INTERMEDIATE STEP
Specific Steps of the Intermediate Step:
1. A carboxyl group is removed from the pyruvate as CO2.
2. The remaining two-carbon fragment is oxidized to form
acetate. An enzyme transfers the pair of electrons to
NAD+ to form NADH.
3. Acetate combines with coenzyme A to form acetyl CoA.
This is what enters the krebs cycle.
Pyruvate (made in the
cytosol via glycolysis) gets
transferred into the
mitochondria (active
transport!). As it comes
in, it loses a carbon (goes
from 3C to 2C) when it
produces one molecule of
CO2. This new 2C
molecule is acetyl CoA.
Acetyl CoA is what goes
into the Krebs cycle. Also,
1 molecule of NADH is
made per pyruvate (so….2
per glucose).
So…summary of
intermediate is 
- 1 glucose  2 acetyl CoA
- 2 CO2 made for each
glucose (b/c 2 pyruvate)
- 2 NADH made for each
glucose
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KREBS/ CITRIC ACID CYCLE
Main Function of the Krebs → to make
electron carriers (NADH and FADH2) to
send to the ETC
Series of 8 steps; Occurs in the
mitochondrial matrix
So…1 glucose produces:
2 ATP
6 NADH
2 FADH2
(remember: 1 glucose = 2 pyruvates)
**Also 2 CO2 released per turn (so 4 for
one glucose)
Acetyl CoA becomes acetate and that
enters the Krebs and combines with
oxaloacetate for form citrate (hence citric
acid cycle)
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Krebs →
Makes 1 ATP, 3
NADH, and 1
FADH2 per turn
The acetyl group of
acetyl CoA joins
the cycle by
combining with the
compound
oxaloacetate,
forming citrate.
The next seven
steps decompose
the citrate back to
oxaloacetate.
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ELECTRON
TRANSPORT
CHAIN (ETC)
Occurs on the inner membrane of the
mitochondria (highly folded to increase SA);
Energy from NADH and FADH2 power ATP
synthesis
The ETC is a series of proteins throughout the
membrane; the electrons lose energy every time
they get passed down the chain
Electron carriers in the chain:
Flavoprotein
Iron-Sulfur Protein
Lipids (Ubiquinone Q)
Cytochromes (iron prosthetic group)
Electron carriers flip between reduced and
oxidized versions as they accept and donate
electrons.
OXYGEN IS THE FINAL ELECTRON ACCEPTOR!!! →
oxygen combines with the electrons and H+ to
make WATER
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Main Goal of the ETC → it’s a
stepwise free energy drop from
food to oxygen; it creates a proton
gradient that powers
chemiosmosis to create ATP via
oxidative phosphorylation (the ETC
makes no ATP directly)
Note: NADH drops off its electrons at a
higher level than FADH2 because their
electrons carry more energy.
The ETC uses energy from the electrons
and pumps the protons OUT of the matrix
into the intermembrane space; it then
diffuses back in via ATP synthase.
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CHEMIOSMOSIS
As electrons flow
down the ETC, H+ are
pumped FROM THE
MATRIX into the
INTERMEMBRANE
SPACE, and the H+
diffuse BACK INTO the
matrix via the ATP
SYNTHASE
Definition → energy coupling mechanism that uses energy stored in the form of a H+
gradient across a membrane to drive work
How it works → as the electrons move down the ETC, the proteins pump H+ OUT of the
matrix and then they use ATP Synthase to allow the H+ to diffuse back in. As the H+
diffuse back in, the ATP Synthase proteins make ATP
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ATP SYNTHASE
ATP Synthase is a
protein that is
powered by the H+
gradient and
converts ADP to
ATP. It works like a
water wheel and
forces a
conformational
change which
activates the
catalytic sites on
ADP to bond with P
to form ATP.
This is how ATP is produced = CHEMIOSMOSIS
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Final e- acceptor
after they go down
the ETC is OXYGEN
(from the
atmosphere) …it
combines with eand H+ to make
WATER
-NADH and FADH2 drop off e- to the ETC
-As the e- get passed down the chain, they lose energy; that energy is used to pump H+
OUT of the matrix into the intermembrane space
-This creates a concentration gradient
-The protons then diffuse back INTO the matrix via the ATP synthase (chemiosmosis);
this creates ATP (oxidative phosphorylation)
-Makes a TON of ATP!!!
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CELLULAR RESPIRATION OVERVIEW
ATP Summary → Substrate
Level Phosphorylation – 4
ATP (2 from Glycolysis and 2
from Krebs); Oxidative
Phosphorylation – 34 ATP
(from ETC)
Efficiency of Respiration →
34% efficient (66% of energy
is lost as heat)
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CELLULAR RESPIRATION VS. FERMENTATION
Oxygen Present → Aerobic
Respiration (efficient!)
Oxygen NOT Present →
Fermentation (not efficient)
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FERMENTATION
If there is no oxygen present (anaerobic) the
pyruvate (from glycolysis) goes to fermentation
 The main goal of fermentation is to make NAD+
to put back into glycolysis; it makes NO ATP on
its own (it just keeps glycolysis going so that it
can make 2 ATP at a time)
 Occurs in cytosol
 2 types of fermentation: alcohol and lactic acid
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ALCOHOLIC FERMENTATION
- Pyruvate is turned into
ethanol
- CO2 is released (bubbles!)
- Done by yeast for brewing,
baking, wine-making
3C Pyruvate → 2C Ethanol
Remember: Goal is to
produce NAD+ to send back
to glycolysis so it can keep
going and produce more
ATP
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LACTIC ACID FERMENTATION
- Pyruvate is turned into Lactate (or lactic
acid)
- Lactate is eventually carried away by the
blood to the liver where it gets converted
back into pyruvate
- The waste product, lactate, was
previously thought to cause muscle
fatigue and pain, but recent research
suggests instead that it may be
increased levels of potassium ions (K+)
- No CO2 is released
3C Pyruvate → 3C Lactate
Remember: Goal is to produce
NAD+ to send back to glycolysis
so it can keep going and
produce more ATP
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LACTIC ACID VS. ALCOHOL FERMENTATION
Both start with pyruvate from
glycolysis
Alcohol makes ethanol and gives
off CO2
Lactic acid makes Lactic acid and
does NOT give off CO2
Both create NAD+ to be sent back
to glycolysis
Neither make any ATP on their own
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FERMENTATION - OVERVIEW
Obligate Aerobes → needs
oxygen; can do respiration
only
Obligate Anaerobes → will
not survive in the presence
of oxygen; fermentation
only
Respiration is 19 times more efficient than fermentation
(38 ATP vs. 2 ATP)
Facultative Anaerobes →
can live with or without
oxygen (if given the choice
they will use the oxygen to
do respiration because it is
so much more efficient);
can do cellular respiration
or fermentation; ex. Human
muscle cells
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The role of glycolysis in both fermentation and
respiration has an evolutionary basis
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Ancient prokaryotes likely used glycolysis to make ATP long
before oxygen was present in Earth’s atmosphere.
The evidence suggests that this pathway evolved very early in
the history of life on Earth.
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WHAT KINDS OF FOOD CAN GO INTO
GLYCOLYSIS? A VARIETY OF MOLECULES CAN BE
USED TO MAKE ATP
Carbohydrates → get broken down into their
monomers and then those monomers get converted
to glucose; glucose is then turned into pyruvate
during glycolysis
Proteins → are broken down to their individual
amino acids and then the amino groups are
removed (called deamination – this nitrogen waste
is then excreted as urea or ammonia); the remaining
carbon skeletons are then put into glycolysis and the
krebs cycle
Fats → glycerol is converted into glyceraldehyde
phosphate (G3P) which is an intermediate of
glycolysis; the FA chains are broken down into 2C
components that enter the Krebs as acetyl CoA
(called beta oxidation)
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FEEDBACK
MECHANISMS OF
RESPIRATION
Phosphofructokinase (PFK) sets the
pace for respiration
- It is STIMULATED by AMP and ADP
- It is INHIBITED by ATP and by
citrate (first product of Krebs)
This ensures that we are only making
as much ATP as we need and not extra
that is just getting wasted.
PFK is regulated allosterically by the
above molecules.
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CELLULAR RESPIRATION ANIMATION
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6 minutes 
https://www.youtube.com/watch?v=Gb2EzF_XqA
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