Ch 9: Cellular
Respiration
The Big Picture
 Cellular
respiration sole purpose is to
produce ATP.
 Its
an exergonic (catabolic)reaction.
Can be summarized as a whole as:
Organic Compound+OxygenCO2+Water
+ATP + heat

Glycolysis, Krebs Cycle, and
Oxidative Phosphorylation
 1.
Glycolysis is the decomposition
of glucose to pyruvate (or pyruvic
acid)
 2.
Krebs Cycle takes pyruvate (2
pyruvate per glucose molecule)
and yields electron acceptors and
ATP.
 3.
Oxidative phosphorylation
extracts ATP from NADH and
FADH2.
Reminder on ATP




ATP (adenosine triphosphate) is a nucleotide
with unstable phosphate bonds that the cell
hydrolyzes for energy.
The cell taps energy stored in ATP by enzymatically transferring terminal phosphate
groups from ATP to other compounds.
The compound receiving the phosphate group
is said to be phosphoralated and is more
reactive as a result.
Cells use ATP to continue cellular work. But
they must replenish the ATP supply to continue
Simply put – cellular respiration is
a redox process that transfers
hydrogen from sugar to oxygen.
• Valence electrons of carbon and
hydrogen lose potential energy as
they shift toward electronegative O.
• Released energy is used by cells
to produce ATP.
Redox reactions




These are the energy-shuttling
mechansisms of metabolism
Partial or complete gain of
electrons=reduction
Partial or complete loss of
electron=oxidation
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
function in the redox reactions and
are found in all cells.
Traps energy-rich electrons from the
organic compound.

NAD+= oxidized coenzyme

NADH= reduced coenzyme
Why isn’t glucose oxidized in one
explosive step?

During oxydation of glucose, NAD+
functions as an oxidizing agent by
trapping energy-rich electrons from
glucose. These reactions are catalized by
enzymes called dehydrogenases which:
- Remove a pair of hydrogen atoms (2 e,2p)
from substrate.
-
Deliver the two electrons and one proton
to NAD+
-
Release the remaining proton into the
surrounding solution.
Cellular Respiration
Glyclolysis (per glucose molecule)
 Takes
place in cytosol.
 Mutiple steps (9 or 10 depending on
source) in the process of
decomposing glucose into pyruvate.
Mg2+ ions are cofactors to help.
 2 ATP go IN
 4 ATP PRODUCED (so what is NET
gain?)
 2 NAD+ go IN
 2 NADH PRODUCED
 2 Pyruvate (Pyruvic acid) PRODUCED
Glycolysis……….
- occurs whether O is present or not
- no CO2 is released as glucose is
oxidized to pyruvate; all C in glu –
cose can be accounted for in the 2
molecules of pyruvate.
- occurs in 2 phases
Glycolysis: Energy Investment Phase
- includes 5 preparatory steps in which
glucose is split in two.
- consumes ATP….why? The cell uses
ATP to phosphorylate the
intermediates of glycolysis.
- End result of this phase is 2 molecules
of glyceraldehyde phosphate (3 C
each) for each glucose molecule.
Glycolysis: Energy – Yielding Phase
- two 3 carbon intermediaries (PGAL)
are oxidized becoming pyruvate.
- there’s a net gain of 2 ATPs by
substrate phosphorylation
- 2 molecules of NAD+ are reduced to
NADH
Glycolysis
• Breaks down “Glucose” (6-carbon sugar) into 2
molecules of “Pyruvic Acid” (3-carbon
compound)
•
• The products are:
–2 Pyruvic Acid molecules
–2 ATP molecules
–2 NADH molecules
Glycolysis has 2 pathways…
If Oxygen is present (Aerobic) ...“Krebs
Cycle”… then to Electron Transport Chain
If Oxygen is absent (Anaerobic) ……..
“Fermentation”occurs
KREBS Cycle (per pyruvate)
 Takes
place in mitochondrial
matrix.
 Pyruvate combines with CoA
(coenzyme A) to make acetyl
CoA. This makes 1 NADH and 1
CO2.
 Acetyl CoA combines with OAA to
form citric acid. (8 steps yielding
intermediate products). 3 NADH
and 1 FADH2 are made and CO2
released. 1 ATP is made.
 How much total ATP then for the
Krebs cycle?
Junction between glycolysis and Krebs Cycle
Is the oxidation of Pyruvate to acetyl CoA.
- CO2 is removed from
the carboxyl group of
pyruvate changing it
from a 3 carbon to a
2 carbon compound.
CO2 is released.
- 2 NADH molecules
are produced
- Coenzyme A attaches
to the acetyl group – very unstable-reactive
KREBS CYCLE
(Aerobic Pathway)
Krebs Cycle oxidizes
the remaining acetyl
fragments of Acetyl –
CoA to CO2.
- Energy released from
this exergonic process
is used to reduce co –
enzymes, NAD and
FAD, and phosphory –
late ATP.
How many ATPs are
produced here?
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
 The
chain is an energy converter
that pumps 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
 The
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
catalyses ATP from ADP and an
inorganic phosphate
 Each NADH produces 3 ATP
 Each FADH produces 2 ATP
To summarize, for each glucose molecule…
 Glycolysis
NADH and
2
makes 2 NET ATP and 2
pyruvate 2 acetyl CoA = 2 NADH
 Krebs
 Since
Cycle: 6 NADH, 2 FADH2, 2 ATP
each NADH produces 3 ATP
during oxidative phosphorylation and
each FADH2 produces 2 ATP…how
many ATP total?
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
FERMENTATION
(Aanerobic Pathway)
1.Alcoholic :
2 TYPES: Alcoholic & Lactic Acid
• Yeast & other microorganisms use
this to produce alcohol & CO2 as
wastes.
• Beer is a beverage made by alcoholic
fermentation
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
(Aanerobic Pathway)
2.Lactic Acid:
– Exercise causes the body needs more
oxygen for respiration to make more
ATP
– Body resorts to lactic acid
fermentation to make ATP
– Lactic Acid is also produced causing
Lactic Acid Fermentation
 Commonly
done by: Muscle cells
during oxygen debt.
 Same
thing as before:
- do glycolysis
- but then to regenerate NAD+, a
byproduct called lactate is made
instead of
acetylaldehydeethanol.
Diagram Assignment



You will diagram the major pathways
to respiration in color in a way that is
understandable to you. Use websites
and the book to help you form
diagrams for each section of
respiration.
It must be in color, complete, and
have words on it to describe what is
happening in the process for full
credit.
Also must have an input/output chart
by each stage: glycolysis, krebs, +
ETC