Download Cellular Respiration

Cellular Respiration

How organisms convert food into usable
energy
The Overall Process

Organic molecule + Oxygen →
Carbon dioxide + Water + Energy
+ O2


C6H12O6 + 6O2 → 6CO2 + 6H20 + Energy
(ATP and heat)
Glucose is a very high energy molecule,
carbon dioxide and water are not.
Cellular Respiration
• Cellular respiration occurs in ALL
eukaryotes (Plants, animals, fungi,
protists) and some bacteria
• Glycolysis (the first step) occurs in ALL
organisms
ATP

Energy from food is not used directly

Energy is transferred in the form of ATP

Food is broken down and the energy
released forms ATP, storing energy in
the bonds between phosphate groups
ATP is Recycled
ATP is formed by combining ADP and Pi.
Energy is released when ATP is split.
Glucose is Oxidized
During Cellular
Respiration


Glucose loses electrons to Oxygen,
which can then bind with H ions and
form water
Molecules with lots of C-H bonds are
good sources of fuel, as they have lots
of energy and electrons

i.e. fat
Remember Activation
Energy, Ea?



Glucose releases a
lot of energy when it
is combusted
However, this
doesn’t happen
spontaneously due
to Ea
Enzymes lower this
energy of activation
and allow the
reaction to occur in
many steps
Electrons Do Not Pass
Directly to O2


Electrons are stripped from glucose
one by one
They are passed to NAD+ to form
NADH
NADH delivers
electrons to the ETC

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

Electrons travel down the Electron
Transport Chain
Each step of the ETC is more
electronegative (wants the electrons
more!)
Small amounts of energy are released in
each step
Electrons eventually reach Oxygen
(remember Oxygen is one of the most
electronegative elements!)
Why So Many Steps?
•Glucose contains a
lot of energy!
•If all of the energy is
released at once,
you would get an
explosion
•Lots of energy is
lost as light and
heat
Cellular Respiration
3 Parts of Cellular
Respiration



Glycolysis

Glucose is oxidized into Pyruvate

Some ATP is made, along with some
NADH
Krebs Cycle

Decomposes Pyruvate to Carbon
Dioxide, making some ATP

Produces NADH and FADH2
ETC/Oxidative Phosphorylation

Produces lots of ATP from NADH and
FADH2
Glycolysis

Literally means “sugar splitting”

Takes place in cytosol

Does not require mitochondria
Net Effects of
Glycolysis

Glucose → 2 Pyruvate + 2 ATP + 2NADH
ATP Synthesized via
Substrate-level
Phosphorylation

Phosphate group is transferred from the
sugar to ADP by an enzyme, forming
ATP
Pyruvate → Acetyl CoA



Before entering the Krebs cycle,
Pyruvate releases a Carbon Dioxide
molecule
The remaining 2 carbons are oxidized to
form acetate, producing NADH
They then combine with a molecule
called Coenzyme A to form Acetyl CoA
The Krebs Cycle

Acetyl CoA enters the Krebs Cycle (aka
Citric Acid cycle)
For every glucose...

2 Acetyl CoAs enter the Krebs cycle

4 CO2 molecules are released


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6 NAD+ molecules are reduced to
NADH
2 FADH2 molecules are formed from
FADH+
2 ATP molecules are formed from ADP
and Pi via Substrate-Level
phosphorylation
Krebs Cycle
In even more detail...
Glycolysis + Krebs
From 1 Molecule of Glucose we have created: 2ATP + 2NADH (glycolysis)
+ 2NADH (Pyruvate → Acetyl CoA) + 6NADH + 2 FADH2 + 2ATP (Krebs
cycle) = 10NADH + 4ATP + 2FADH2
Most ATP is Produced
via the Electron
Transport Chain



A series of proteins, each is more
electronegative than the protein before it
So electrons give off a little energy each
time as they are passed down the chain
Electrons eventually end up at O2
The Mitochondrial ETC

Found in the inner membrane (cristae)
NADH and FADH2 Hand
off Electrons to the ETC

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NADH and FADH2 drop off their
electrons at different points in the
ETC
NADH drops off electrons to FMN at
the top of the chain
FADH2 drops off electrons a little
ways into the chain

FADH2 will produce less ATP
Chemiosmosis


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Each time an electron moves, an
H+ ion is pumped across the
membrane
This creates an electrochemical
gradient as there is a much greater
concentration of H+ ions in the
intermembrane space
The only way H+ ions can diffuse
into the matrix is through ATP
synthase
Pumping Protons
ATP Synthase
Mechanism of ATP
Synthase


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Diffusing protons turn a cylinder
(like water pushing a mill)
This causes the cylinder to
essentially spin – changing the
shape of the enzymatic regions of
the protein
This activates the
enzyme, synthesizing
ATP
ATP Synthase
produces ATP as H+
ions diffuse through it
Oxygen reduced to
Water

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Electrons at the end of the chain are
donated to oxygen.
Oxygen, with these new electrons, can
combine with H+ ions to form water.
4H+ + 4e- + O2 → 2H2O
For each molecule of
Glucose...


34 ATPs are synthesized via oxidative
phosphorylation
Each NADH produces 3 ATP


10NADH*3ATP = 30 ATP
Each FADH2 produces 2 ATP

2FADH2*2ATP = 4 ATP

Total = 34 ATP (roughly)

(plus 6 molecules of Water)
Review of Respiration
Chemical Summary
C6H12O6 + 6O2 + 38ADP + 38Pi
→ 6CO2 + 6H20 + 38 ATP
Efficiency of Cellular
Respiration

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40% of the energy is converted to ATP
Although it may sound low, this is a
remarkably high amount
Cars at the most convert about 25% of
their fuel to usable energy
The rest of the energy is lost as heat per
the 2nd Law of Thermodynamics
(entropy!)
Cellular Respiration
• Occurs in all eukaryotes and some
bacteria
• Glycolysis occurs in cytosol of
ALL cells
• The rest of respiration occurs in
mitochondria
• Krebs cycle in the
mitochondrial matrix
• ETC is in the inner membrane
Review
• Glyolysis – Sugar split, forming
ATP and NADH
• Krebs cycle – sugar fully broken
down to CO2 forming NADH and
FADH2
• Oxidative phosphorylation –
lots of ATP made via
chemiosmosis
Aerobic Respiration

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The process we
have learned is
aerobic respiration
Oxygen is
necessary
Glycolysis →
Krebs Cycle →
Oxidative
Phosphorylation

Lots of ATP
produced
Anaerobic Respiration



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ATP can be made
without oxygen (just
not as much)
Glycolysis makes 2
ATP
NAD+ can oxidize
glucose to pyruvate,
generating ATP
But we must
regenerate NAD+ as it
is converted to NADH
in glycolysis
This is solved by
fermentation
Alcohol Fermentation
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In alcohol
fermentation
pyruvate is
converted to
ethanol,
regenerating NAD+
Yeast are used to
make alcoholic
beverages
Generates CO2
Lactic Acid Formation


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Muscle cells can
generate some ATP
without oxygen
Glycolysis occurs
Fermentation
converts pyruvate
to lactate,
regenerating NAD+
Lactic Acid Build-Up


When muscle cells
cannot get oxygen
fast enough (i.e.
when you're
sprinting) Lactic
Acid Fermentation
occurs
Build up of lactic
acid is what makes
muscles feel heavy
and tired


Lactic acid is
carried to liver
where pyruvate can
be regenerated
Lactic acid is also
important in the
making of cheese
and yogurt
Glycolysis Evolved
Early

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Glycolysis evolved
long before oxygen
was present in the
atmosphere

All cells undergo
glycolysis
Aerobic respiration
provides much more
ATP, but some
organisms can
survive only by
fermentation
Some organisms
(and cells) can
switch switch
between
fermentation and
aerobic respiration


i.e. muscle
cells
If oxygen is present,
pyruvate enters
Krebs cycle, if not it
heads to
fermentation
Other Sources of Fuel


Starch and
glycogen can be
broken down to
glucose
Proteins can be
converted to
intermediates of
respiration

Fatty Acids can be
broken down to 2carbon fragments
that enter the Krebs
cycle via Beta
Oxidation

Provides lots of
ATP
Feedback Inhibition

When excess ATP is present, it shuts off
glycolysis, preventing accumulation of
ATP and preserving energy stores