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Cellular Respiration
Honors Biology
What is Cellular Respiration?
The process of converting food energy
into ATP energy
C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + 36 ATP
Why are both Photosynthesis and Cell
Respiration important to Ecosystems?
Light is the ultimate
source of energy for all
ecosystems
Chemicals cycle and
Energy flows
Photosynthesis and
cellular respiration are
complimentary
reactions
Why do plants need both
chloroplasts and mitochondria?
Chloroplasts use
energy from the
sun to make
glucose
Mitochondria
convert glucose to
ATP—the energy
currency of the cell
What is ATP?
Adenosine Triphosphate
– 5-Carbon sugar (Ribose)
– Nitrogenous base
(Adenine)
– 3 Phosphate groups
Energy currency of the
cell
The chemical bonds that
link the phosphate groups
together are high energy
bonds
When a phosphate group
is removed to form ADP
and P, small packets of
energy are released
How is ATP used?
As ATP is broken down, it
gives off usable energy to
power chemical work and
gives off some nonusable
energy as heat.
Synthesizing molecules for
growth and reproduction
Transport work – active
transport, endocytosis, and
exocytosis
Mechanical work – muscle
contraction, cilia and flagella
movement, organelle
movement
Why use ATP energy and not
energy from glucose?
Breaking down glucose yields too much energy
for cellular reactions and most of the energy
would be wasted as heat.
1 Glucose = 686 kcal
1 ATP = 7.3 kcal
1 Glucose → 36 ATP
How efficient are cells at converting glucose into
ATP?
– 38% of the energy from glucose yields ATP,
therefore 62% wasted as heat.
Cellular Respiration is a Redox Reaction
(Oxidation)
C6H12O6 + 6 O2 → 6 CO2 + 6 H2O
(Reduction)
Oxidation is the loss of electrons or H+
Reduction is the gain of electrons or H+
Glucose is oxidized when electrons and H+ are passed
to coenzymes NAD+ and FAD before reducing or
passing them to oxygen.
Glucose is oxidized by a series of smaller steps so
that smaller packets of energy are released to make
ATP, rather than one large explosion of energy.
Cell Respiration can be divided into 4 Parts:
1)
2)
3)
4)
Glycolysis
Oxidation of Pyruvate / Transition Reaction
The Krebs Cycle
The Electron Transport Chain and
Chemiosmotic Phosphorylation
Where do the 4 parts of Cellular
Respiration take place?
Glycolysis:
– Cytosol
Oxidation of
Pyruvate:
– Matrix
The Krebs Cycled:
– Matrix
Electron Transport
Chain and
Cheimiosmotic
Phosphorylation:
– Cristae
Parts of the Mitochondria
Anaerobic Respiration (no oxygen required, cytoplasm)
1. Glycolysis
(substrate level)
Glucose
2 ATP

4 ATP (Net 2 ATP)
2 NADH
2 Pyruvate
Aerobic Respiration (oxygen required, mitochondria)
2. Oxidation
of
Pyruvate
2 Pyruvate

2 CO2
2 NADH
2 Acetyl CoA
3. Krebs Cycle
(substrate level)
2 Acetyl CoA

4 CO2
2 ATP
6 NADH
2 FADH2
4. Electron
Transport
Chain
(chemiosmotic)
10 NADH
2 FADH2
6 O2

32 ATP
6 H 2O
Total: 36 ATP produced
ATP is made in two ways:
1) Substrate Level
Phosphorylation (glycolysis
& Krebs cycle)
2) Chemiosmotic
Phosphorylation (electron
transport chain)
Substrate-Level
Phosphorylation:
Energy and phosphate are
transferred to ADP using an
enzyme, to form ATP.
Phosphate comes from one
of the intermediate
molecules produced from
the breakdown of glucose.
Glycolysis
Glucose
2 ATP

2 Pyruvate
4 ATP (Net 2 ATP)
2 NADH
Glucose (C6) is split to make
2 Pyruvates (C3)
– 1st: ATP energy used to phosphorylate
glucose (stored energy)
– 2nd: phosphorylated glucose broken
down into two C3 sugar phosphates
– 3rd: the sugar phosphates are oxidized
to yield electrons and H+ ions which are
donated to 2 NAD+ → 2 NADH (stored
electron and hydrogen for the Electron
Transport Chain)
– 4th: The energy from oxidation is used
to make 4 ATP molecules (net 2 ATP)
This is substrate level phosphorylation
because an enzyme transfers
phosphate to ADP making ATP
Glycolysis produces very little ATP
energy, most energy is still stored in
Pyruvate molecules.
Oxidation of Pyruvate /Transition Reaction
2 Pyruvate

2 CO2
2 NADH
2 Acetyl CoA
When Oxygen is present,
2 Pyruvates go to the
matrix where they are
converted into 2 Acetyl
CoA (C2).
Multienzyme complex:
– 1st: each Pyruvate releases
CO2 to form Acetate.
– 2nd: Acetate is oxidized and
gives electrons and H+ ions
to 2 NAD+ → 2 NADH.
– 3rd Acetate is combined
with Coenzyme A to
produce 2 Acetyl CoA
molecules.
2 NADH’s carry electrons
and hydrogens to the
Electron Transport Chain.
The Krebs Cycle / Citric Acid Cycle
2 Acetyl CoA

4 CO2
2 ATP
6 NADH
2 FADH2
8 Enzymatic Steps in Matrix of
Mitochondria: Break down and Oxidize
each Acetyl CoA (2-C’s) to release 2 CO2
and yield electrons and H+ ions to
3 NAD+ + 1 FAD → 3 NADH + FADH2.
This yields energy to produce ATP by
substrate level phosphorylation.
The first step of the Krebs cycle combines
Oxaloacetate (4 C’s) with Acetyl CoA to
form Citric Acid, then the remaining 7
steps ultimately recycle oxalacetate.
Two Turns of the Krebs Cycle are required
to break down both Acetyl Coenzyme A
molecules.
The Krebs cycle produces some chemical
energy in the form of ATP but most of
the chemical energy is in the form of
NADH and FADH2 which then go on to
the Electron Transport Chain.
The Electron Transport Chain
10 NADH
2 FADH2
Oxygen

32 ATP
H2O
NADH and FADH2 produced
earlier, go to the Electron
Transport Chain.
NADH and FADH2 release
electrons to carriers/proteins
embedded in the membrane
of the cristae. As the
electrons are transferred, H+
ions are pumped from the
matrix to the intermembrane
space up the concentration
gradient. Electrons are
passed along a series of 9
carriers until they are
ultimately donated to an
Oxygen molecule.
½ O2 + 2 electrons + 2 H+
(from NADH and FADH2) →
H2O.
http://vcell.ndsu.nodak.edu/animations/etc/movie.htm
Chemiosmotic Phosphorylation
Hydrogen ions travel down their concentration gradient through a channel
protein coupled with an enzyme called ATP Synthase.
As H+ ions move into the matrix, energy is released and used to combine
ADP + P → ATP.
Hydrogens are recycled and pumped back across the cristae using the
Electron Transport Chain.
ATP diffuses out of the mitochondria through channel proteins to be used
by the cell.
http://vcell.ndsu.nodak.edu/animations/atpgradient/movie.htm
ATP Synthase
Multisubunit complex
with 4 parts:
– Rotor – spins as H+ ions flow
– Stator – holds the rotor and
knob complex together in the
cristae
– Internal Rod – extends
between rotor and knob, spins
when rotor spins which then
turns the knob
– Knob – contains 3 catalytic
sites that when turned change
shape and activate the enzyme
used to make ATP
Review ATP Production:
1)
2)
3)
4)
Glycolysis → 2 ATP
Oxidation of Pyruvate → No ATP
The Krebs Cycle → 2 ATP
The Electron Transport Chain and
Chemiosmotic Phosphorylation:
– Each NADH produces 2-3 ATP so
10 NADH → 28 ATP
– Each FADH2 produces 2 ATP so
2 FADH2 → 4 ATP
Total = 36 ATP
1 Glucose = 686 kcal
1 ATP = 7.3 kcal
1 Glucose → 36 ATP
How efficient are cells at converting
glucose into ATP?
– 38% of the energy from glucose
yields ATP, therefore 62% wasted as
heat (used to maintain body
temperature or is dissipated)
– Ex. Most efficient Cars: only 25% of
the energy from gasoline is used to
move the car, 75% heat.
All Types of Molecules can be used
to form ATP by Cell Respiration:
Proteins, Carbohydrates,
and Lipids must first be
broken down into their
monomers and absorbed
in the small intestine.
Monomers may be
further broken down into
intermediate molecules
before entering different
parts of Cell respiration
to ultimately form ATP.
Anaerobic Respiration: Fermentation
If there is NO oxygen, then cells can make ATP by Fermentation
Without oxygen, Oxidation of Pyruvate and the Electron Transport
Chain do not operate.
Glucose
→
NAD+ Glycolysis
Pyruvate
2 NADH
2 ATP
→
Reduction Rxn
Lactate
or
Alcohol + CO2
Fermentation yields a net gain of 2 ATP by substrate level phosphorylation
for every 1 Glucose. (Inefficient)
Two Forms of Fermentation:
Lactic Acid Fermentation (animals)
Alcohol Fermentation (yeast)