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7-2: Aerobic Respiration
 In
most cells, glycolysis does not result in
fermentation.
 Instead, if O2 is available, pyruvic acid
undergoes aerobic respiration, or
cellular respiration that requires O2

Also known as oxidative respiration
Overview of Aerobic Respiration
Aerobic Respiration has 2 major stages:

1.
2.
Krebs Cycle – oxidation of glucose is
completed; makes molecules of NADH;
produces a small amount of ATP
Electron Transport Chain +
Chemiosmosis – uses NADH to make ATP;
produces most of the ATP
Prokaryotes vs. Eukaryotes
 In
Prokaryotes, the reactions of the Krebs
Cycle and ETC takes place in the cytosol
of the cell
 In Eukaryotes, the reactions of the Krebs
Cycle and ETC takes place in the
mitochondria


Pyruvic acid diffuses across the membrane of
mitochondria into the mitochondrial matrix
The matrix contains enzymes needed to
catalyze the rxns of the Krebs cycle
Overview (cont.)
 Pyruvic
acid reacts with a molecule called
Coenzyme A to form acetyl CoA

CO2 is given off and NAD+ is reduced to
NADH
Stage I - Krebs Cycle
 Biochemical
pathway that
breaks down acetyl CoA
producing CO2, H atoms, + ATP

AKA – TCA Cycle or Citric Acid
Cycle
 Identified
+ named after
German scientist Hans Kreb
 Reactions take place in the
mitochondrial matrix
Krebs Cycle (5 Steps)
Acetyl CoA combines w/ a 4-C
compound, oxaloacetic acid to produce
a 6-C compound, citric acid.
1.

Reaction regenerates coenzyme A
Krebs Cycle
2.
Citric acid releases a CO2 and H to form
a 5-C compound


Citric acid gets oxidized
H atom transfers to NAD+ - - NAD+ reduced
to NADH
Krebs Cycle
3.
The 5-C compound releases a CO2
molecule and H to form a 4-C compound


NAD+ is reduced to NADH
ATP created from ADP
Krebs Cycle
4.
The 4-C compound releases a H atom to
form another 4-C compound
H transferred to FAD (accepts e- during
redox)

•
FAD gets reduced to FADH2
Krebs Cycle
5.
The 4-C compound releases a H atom to
regenerate oxaloacetic acid, which
keeps the Krebs cycle going

NAD+ reduced to NADH
Krebs Cycle
 Video
clip
What’s been accomplished thus far…
 One
glucose molecule = 2 pyruvic acid
molecules = 2 acetyl CoA molecules = 2
turns of Krebs Cycle
 These turns produce:




6 NADH
2 FADH2
2 ATP
4 CO2
 NOT
ENOUGH ENERGY TO LIVE OFF
OF…
So what now?
 Use
our energy-carrying molecules
• NADH + FADH2
• Total # of Molecules:
 10 NADH (2 – Gly; 2 – PA to Acetyl
CoA; 6 – Krebs)
 2 FADH2 (2 – Krebs)
 Take
them and go to next stage of AR……
• THE ELECTRON TRANSPORT CHAIN
Stage II – ETC + Chemiosmosis
 Series
of molecules that transfer electrons
from one molecule to another
 In Eukaryotes, the ETC takes place in the
inner membrane of mitochondria
 In Prokaryotes, the ETC takes place in the
cell membrane

ATP is produced by ETC when NADH +
FADH2 release H atoms
THE ELECTRON TRANSPORT CHAIN
(5 Steps)
1.
NADH + FADH2 donate electrons to the
ETC. They also donate protons (H+)


NADH – 3 eFADH2 – 2 e-
• NADH = 10 * 3 = 30 total e• FADH2 = 2 * 2 = 4 total e-
ETC (cont.)
2.
The e- are passed along a chain from
molecule to molecule in a series of redox
reactions. As they are passed, they lose
energy.
ETC (cont.)
3.
The energy lost by electrons are used to
pump protons from the matrix outside the
inner mitochondrial membrane (cristae).
A concentration gradient and electrical
gradient are created.
ETC (cont.)
4.
The concentration + electrical gradients
drive the synthesis of ATP by
Chemiosmosis. As protons move through
molecules of ATP synthase, ATP is made
from ADP + phosphate
ETC (cont.)
5.
The final acceptor of electrons is oxygen.
It also accepts protons and combines to
make molecules of water
ETC (cont.)

Note: If electrons weren’t
able to be picked up by
oxygen at the end of the
ETC chain, the entire
process of chemiosmosis
would stop!

NO ATP MADE
FOR CELLS TO
DO WORK
Efficiency of Cellular Respiration
 ATPs

produced ~ 38
Actually get only 36 ATPs due to active
transport of NADH molecules across cristae of
mitochondria
 Cellular



Respiration Efficiency ~ 39%
20x more efficient that glycolysis alone
More efficient than most machines (25%)
Some energy lost as heat
Energy Yield of
Cellular Respiration
What is the equation for the complete
oxidation of glucose?
C6H12O6
+ 6O2 -----> 6CO2
+ 6H20 + energy (heat and
ATP)
 In
addition to glucose, other compounds
can be broken down by cells as a source
of fuel. They can also enter Glycolysis
and/or the Krebs Cycle at any time to yield
more energy to an organism.
 What are these other compounds?



FATS
PROTEINS
CARBOHYDRATES
Why isn’t CR the reverse of
Photosynthesis?
 Involve


P – Light Rxns (ETC/Chemiosmosis) +
Calvin Cycle
CR – Glycolysis, Krebs Cycle,+
ETC/Chemiosmosis
 Occur


different biochemical reactions
at different sites in cells
P – Chloroplasts
CR - Mitochondria
Functions of CR
 Major:

CR provides the ATP that all cells need to
support the activities of life
• Body uses 100,000,000,000,000,000,000 (1x1020)
ATP each second
 Minor:

Building of macromolecules
• Can’t get them from food – so must be
made from compounds in Glycolysis +
Krebs Cycle
C.R. video
Video Recap