Ch 9: Respiration
The Big Picture
 Cellular
respiration has the sole
purpose to produce ATP.
 Its an exergonic reaction.
 Can be summarized as a whole as:
Glucose + Oxygen CO2 + Water+ ATP
Reminder on ATP
 ATP
(adenosine triphosphate) is a
nucleotide with unstable phosphate
bonds that the cell hydrolyzes for
energy.
 Cells use ATP to continue cellular
work. But they must replenish the
ATP supply to continue cellular work.
Respiration does this.
Redox reactions
 These
are the energy-shuttling
mechansisms of metabolism
 Gain a Proton or Electron=reduction
 Loss of an Electron=oxidation
 LEO GER
 They are always coupled…so in order
for a material to lose an electron,
another molecule must accept it
The NAD+, NADH, FAD+, FADH
 NAD+
and FAD+ are coenzymes that
functions in the redox reactions and
is found in all cells.
 It traps energy-rich electrons from
glucose or food.
 NAD+= oxidized coenzyme (lost an
electron)
 NADH= reduced coenzyme (gained a
proton)
Why glucose? C6H12O6
 It’s
the energy source used most
often by living organisms.
 Keep in mind that fats and proteins
could also be considered but glucose
is the “hallmark” molecule to use in
cellular respiration
Respiration is divided into three
parts: Glycolysis, Krebs Cycle, and
Oxidative Phosphorylation
1. Glycolysis is the decomposition of
glucose to pyruvate (or pyruvic acid).
 2. Krebs Cycle (oxidative
phosphorylation) takes pyruvate (1
pyruvate) and yields electron acceptors
and ATP.
 3. ETC (Oxidative phosphorylation)
extracts ATP from NADH and FADH2.

Glyclolysis (per glucose molecule)
Takes place in cytosol.
 There are 9 intermediate steps is the
process of decomposing glucose into
pyruvate. Mg2+ ions are cofactors to help.
 One molecule of glucose goes IN
 2 ATP go IN
 4 ATP PRODUCED (so what is NET?)
 2 NAD+ go IN
 2 NADH PRODUCED
 2 Pyruvate (Pyrivic acid) PRODUCED

KREBS Cycle (per pyruvate)
Takes place in mitochondrial matrix.
 Pyruvate combines with CoA (coenzyme
A) to make acetyl CoA. This makes 2
NADH and CO2.
 Acetyl CoA combines with OAA to form
citric acid…which is why Krebs can also be
the Citric Acid Cycle. (7 intermediate
products). 6 NADH and 2 FADH2 are
made and CO2 released. 2 ATP is
made.
 How much total ATP then for Krebs?

ETC (Oxidative Phosphorylation)
Takes place in inner mitochondrial
membrane
 Involves a passing of electrons through a
series of membrane associated electron
carriers in the mitochondria to ultimately
produce ATP
 You shuffle electrons to pump protons
across the mitochondiral membrane
against a concentration gradient to help
establish a proton gradient

The ETC transports electrons from NADH
and FADH2 along a transport chain
 The respiratory chain is composed of 4
enzyme complexes and carriers called
cytochrome c and ubiquinone (Q). The 1st
two complexes shuttle the electrons of
NADH + H+ and FADH2 to Q.
 The third complex moves electrons from Q
to chytochrome c.
 The final complex passes electrons to O2,
an ultimate acceptor, which results in
H20 as a by-product

 That
chain is an energy converter
that pumped H+ across the
membrane. How? Certain members
along the electron transport chain
accept and release protons along
with electrons. A gradient is created
that is referred to as the protonmotive force
 Now this H+ has the capacity to do
work
http://www.sci.uidaho.edu/bionet/biol115/t4_energy/etc.htm
 This
electron transport chain made
no ATP directly, but it did ease the
fall of electrons from food to oxygen
 So now, by chemiosmosis, it will
couple this electron transport and
energy release to ATP synthase
 ATP synthase is an enzyme that
actually MAKES ATP from ADP and
inorganic phosphate
 Each NADH produces 3 ATP
 Each FADH produces 2 ATP
To summarize…
Glycolysis makes 2 NET ATP and 2 NADH
 2 pyruvate 2 acetyl CoA= 2 NADH
 Krebs Cycle: 6 NADH, 2 FADH2, 2 ATP


Since each NADH produces 3 ATP during
oxidative phosphorylation and each FADH2
produces 2 ATP…how many ATP total?
In Reality…
It would appear we get 38 ATP. But we
don’t in reality. This is because glycolysis
only occurs in the cytoplasm and each
NADH produced there must be transported
into the mitochondria for oxidative
phosphorylation. The transport of NADH
across the mitochondrial matrix reduces
the yield of these NADH in glycolysis to
only 2 ATP.
 That means in reality 36 ATP only.

Wait…but what if there is no
oxygen
What will be affected? Well now there is
no electron acceptor to accept electrons at
the end of the ETC. NADH will
accumulate. Once all NAD+ has been
made to NADH, Krebs and glycolysis will
eventually stop.
 We have to free NAD+ to allow glycolysis
to continue! We must release some NAD+
for use by glycolysis

Alcoholic Fermentation
 Commonly done by yeast in an anaerobic
environment.
 1) Glycolysis is done as normal. And
then, to regenerate the NAD+…
 2) Pyruvate  acetaldehyde
 3) Acetaldehyde ethanol…the energy in
NADH is used to drive this reaction and
this will release NAD+. For each
acetaldehyde, 1 ethanol is made and 1
NAD+ is produced.
 Now we have made 2 ATP from glyocolysis
for each 2 converted pyruvate
Or…we can do Lactic Acid
Fermentation
 Commonly
done by: Muscle cells in
an oxygen debt.
 Same thing as before:
-do glycolysis
-but then to regenerate NAD+, a
byproduct called lactate is made
instead of acetylaldehydeethanol.