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ENERGETICS
Laws of Thermodynamics
 #1 – Energy can be transferred
and transformed, but not created
or destroyed. (Conservation of
energy)
 #2 – Every energy transfer
/transformation increases the
entropy (disorder) of the
universe.
Coupled Reactions
Living organisms appear to “cheat”
the thermodynamic laws because
they develop “order”, however, they
are essentially “open systems” and
receive and release energy by
coupling reactions of metabolism.
Metabolism
 All the chemical processes in the
body can be categorized as
either anabolic (energy-requiring
in order to build up) or catabolic
(energy-releasing for
breakdown).
 They work in concert with each
other to meet the needs of the
organism.
Respiration
The process of extracting stored
energy from glucose to form ATP
C6H12O6 + 6O2 6CO2 + 6H20
+ ATP(energy)
Aerobic Respiration
 Consists of 3 phases
 Glycolysis
 Krebs Cycle
 Oxidative Phosphorylation aka
Electron Transport Chain
Glycolysis
 Literally means “sugar-breaking”
 Glucose is broken down in a
series of reactions, each by an
enzyme. Magnesium ions (Mg2+)
are cofactors that aid enzyme
action.
 Takes place in the cytoplasm.
The final product from the
breakdown of glucose is
pyruvic acid.
In order to start the reactions
some activation energy is
supplied in the form of 2 ATP
molecules.
Glycolysis Summary
 2 ATP supply energy.
 2 NADH (coenzyme) are
produced as electrons are
released during the breakdown.
 4 ATP are produced.
 2 pyruvic acid molecules (3 C)
result.
 Net gain of 2 ATP.
Crossroads
 Depending on the presence of
oxygen, determines what
happens to the pyruvic acid next.
 Without oxygen, the process of
fermentation will occur. We will
explore that process later.
 But we can extract more energy,
if O2 is present, let’s take a look!
 Pyruvic acid (pyruvate) binds to
coenzyme A to form acetyl CoA,
releasing CO2 and electrons
(picked up by NADH) just prior to
entering the cycle. (2 C)
Kreb’s Cycle
 This cycle of reaction occurs in
the matrix of the mitochondrion.
 Although the Kreb’s cycle does
not use oxygen directly, the
molecules required to keep it
running, do require it in order to
be recycled.
Kreb’s Cycle
 In the course of the cycle, the
initial molecule (Acetyl CoA) is,
first combined with a 4C
compound (Oxaloacetate) to
form a 6C compound (Citric
Acid*) and then subsequently
broken apart, piece by piece w/
more energy and CO2 released.
*Kreb’s cycle aka Citric Acid Cycle.
Watch the cycle in motion.
Please note that this animation is oversimplified,
but you should see the basic breakdown of the
molecule and the subsequent results.
Kreb’s Cycle* Intermediate Reactions
The breakdown reactions can generally be
categorized as one of the three:
 Phosphorylation
 Redox
 Isomerization
*also Glycolysis intermediate
reactions
A Closer Look
 Phosphorylation –
changes the shape of
the molecule, thus
allowing work to be
performed.
A Closer Look
 Redox reactions release energy when
electrons move closer to electronegative
atoms.




The loss of electrons is called oxidation.
The addition of electrons is called reduction.
More generally: Xe- + Y -> X + YeX, the electron donor, is the reducing agent and
reduces Y.
 Y, the electron recipient, is the oxidizing agent and
oxidizes X.
 If the degree of electron sharing changes it is
also considered a redox reaction.
A Closer Look
 An example of redox is when hydrogen
atoms are stripped from glucose and
passed to a coenzyme, like NAD+
(nicotinamide adenine dinucleotide).
 Enzymes strip two hydrogen atoms from
glucose, pass two electrons and one
proton to NAD+ and release H+.
 This changes the oxidized form, NAD+,
to the reduced form NADH.
A Closer Look
 Isomerization – molecule changes shape but
retains the same molecular formula.
Kreb’s Cycle Summary
 The released energy is picked up by
1 ATP, 3 NADH and 1 FADH2.
 1 molecule of CO2 is released. The
CO2 is considered waste and we
exhale it.
 Since two molecules of pyruvate,
from the 1 glucose molecule, go
through this cycle, the amounts
above are actually doubled.
A Closer
Look
Summary so far…
Glucose
Molecule
2 pyruvate
6 Carbon
dioxide
ATP
NADH
Net gain
of 4:
10 total:
4-2=2
8 Kreb’s
glycolysis
2 Kreb’s
2 glycolysis
FADH2
2 Kreb’s
Electron Transport Chain
aka Electron Transport System
 Occurs in the cristae of
mitochondrion.
 Electrons from NADH & FADH2
are passed (like a hot potato)
through a chain of cytochrome
molecules.
 This regenerates NAD+ and FAD
so that they can be reused in
glycolysis and Kreb’s cycle.
ETC or ETS
 Oxygen is needed to accept the
electrons, together with H+ ions,
at the end of the chain, forming
water.
 More importantly, a lot of ATP is
generated through this process
called oxidative phosphorylation.
A Closer Look
•Electrons carried by
NADH are transferred to
the first molecule in the
electron transport chain,
flavoprotein.
•The electrons carried by
FADH2 have lower free
energy and are added to
a later point in the chain.
Oxidative Phosphorylation
 The maximum output from
ox-phos is 3 ATP/NADH and 2
ATP/FADH2
Calculate how many ATP can be
produced during this process
from the 1 molecule of glucose.
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Chemiosmosis
 A major part of oxidative
phosphorylation, this basic
process also occurs in
chloroplasts.
 The energy lost from electrons
passing through the ETS, is
used to phosphorylate
ADP to ATP. (coupling reactions)
 Chemiosmosis involves coupled
reactions, where the products of
one reaction are used in another
reaction.
 In this case, the initial products
are H+ ions, which are released
from NADH and FADH2.
 These protons are pumped out
of the fluid matrix, across the
cristae, to the intermembrane
space of the mitochondrion.
 A pH and electrical gradient is
formed as the protons
accumulate, forming a reservoir
of potential energy.
 The protons flow back into the
matrix through channel proteins
called ATP synthases.
 This flow generates the energy
to produce ATP.
 At the end of the ETS, the
moving electrons, which first
served to provide the H+ ions
(protons) when the bonds of
NADH and FADH2 were broken,
are transferred to oxygen and
coupled with the pumped H+ ions
(back in the matrix), form water.
A Closer
Look
http://www.youtube.com/watch?v=3y1dO4nNaKY
How efficient is respiration in
generating ATP?
Complete oxidation of glucose releases 686 kcal
per mole.
Formation of each ATP requires at least 7.3
kcal/mole.
Efficiency of respiration is 7.3 kcal/mole x 38
ATP/glucose/686 kcal/mole glucose = 40%.
The other approximately 60% is lost as heat.
Cellular respiration is remarkably efficient in
energy conversion.
Whew!
 Now you can see why cell
respiration leads to some of the
top 40 ways you know you’ve
been traumatized by AP Biology.
 In the end, if you remember
nothing else, remember what
results after each phase or cycle.
It’s not quite over yet, remember we said that there is an
alternative path if no oxygen was present? Well…….
FERMENTATION
How Glycolysis keeps going if there
is no oxygen.
When there is no Oxygen
why is Fermentation
necessary?
W/O O2, glycolysis is the ONLY
chemical reaction to release energy
from glucose.
Cells need to continuously carry out
glycolysis, but eventually the NAD can
be used up.
If all the NAD is used up, then glycolysis
jams or stops.
 Why would it be disastrous for the
cell if glycolysis stops?
It would run out of energy.
What does Fermentation do in
order to help glycolysis
continue?
 In Fermentation, chemical reactions occur
that free up the NAD, thus regenerating it for
use in glycolysis.
 The electron energy released from NADH+
(What NAD is called when it carries the high
energy electrons)
is put back into pyruvic acid. This chemical
reaction results in a new product.
 Fermentation ONLY occurs if there is no
oxygen.
Products of Fermentation
 In animals, the new product formed is
lactic acid.
 This often forms in muscles when they
can’t get the oxygen they need fast
enough.
 Lactic acid accumulating in muscles is
painful, but this chemical can later be
broken down to extract energy when
enough oxygen is present.
Products of Fermentation
 In yeast, the new products formed are
alcohol and carbon dioxide.
 People put both these products to use
to make wines and cause bread dough
to rise.
Fermentation Review

In your notes write your answers in your own words.
How does fermentation help a cell release
energy from glucose?
Compare and contrast lactic acid
fermentation
and alcoholic fermentation.
What would happen to fermenting wine
if there was an air leak in the
fermentation tank?