Cellular Respiration:
Electron Transport
Chain
Ch. 9
Ms. Springstroh
AP Biology
Adapted from Ms. GaynorDay and Mr. Grant
What’s the
point?
The point
is to make
ATP!
ATP
AP Biology
2006-2007
ATP accounting so far…
 Glycolysis  2 ATP
 Kreb’s cycle  2 ATP
 Life takes a lot of energy to run, need to
extract more energy than 4 ATP!
There’s got to be a better way!
I need a lot
more ATP!
AP Biology
A working muscle recycles over
10 million ATPs per second
Stage #3: Oxidative
Phosphorylation
(Electron Transport Chain (ETC) + Chemiosmosis)

Chemiosmosis is a process which
connects the processes of electron transport
and ATP synthesis

NADH and FADH2
Drop off e-’s at ETC, which powers
ATP synthesis using oxidative
phosphorylation
**OCUURS IN CRISTAE
(folds of inner membrane)
Mitochondria

Double membrane
 outer
membrane
 inner membrane
highly folded cristae
 enzymes & transport
proteins

 intermembrane

space
fluid-filled space between
membranes
Oooooh!
Form fits
function!
What is “oxidative
phosphorylation”?
Recall…
H+/e-’s away, molecule = “oxidized”
 Give H+/e-’s, molecule = “reduced”
 Give phosphate  molecule = “phosphorylated”
 Take

So…oxidative phosphorylation =
process that couples removal of H+’s/ e-’s
from one molecule (NADH or FADH2) &
giving phosphate molecules to another
molecule (ADP)
Difference between oxidative
phosphorylation & substrate-level
phosphorylation


Oxidative phosphorylation: generates ATP when
electrons are taken from NADH or FADH2 (which
become oxidized) and go down the electron
transport chain. This causes Pi (inorganic
phosphate) to join with ADP to form ATP.
Substrate-level phosphorylation: generates ATP
when an enzyme takes a phosphate from a
substrate molecule and gives it directly to ADP.
The Pathway of
Electron Transport
 In
the ETC…
fall from glucose to oxygen not
directly, rather in a series of steps. As
the e-’s fall from step to step, energy
e-’s
is released in manageable
amounts.
**NEEDS O2 TO PROCEED
(unlike glycolysis)
ETC Characteristics



Occurs in cristae, which increase surface area of
inner mitochondrial membrane  allows more
ATP to be produced
ETC takes e-’s from NADH/FADH2 and gives them
to O2
O2 “pulls” e-’s “down” ETC due to
electronegativity (high affinity for e-’s)
What happens at the end of
the ETC chain?
 Electrons
are passed to oxygen,
forming water
O 2
= final e- acceptor
How ETC generates ATP

ETC does NOT make ATP directly but
provides the stage for chemiosmosis to
occur
energy from “falling” e-’s (exergonic) in the
ETC is used to pump H+’s from mitochondrial
matrix to intermembrane space
 Results in a H+ (proton) gradient inside
mitochondria
 The
Inside (matrix) = low [H+]
 Outside (intermembrane space)
= high [H+]

http://highered.mcgrawhill.com/olcweb/cgi/pluginpop.cgi?it=swf::53
5::535::/sites/dl/free/0072437316/120071/bi
o11.swf::Electron%20Transport%20System
%20and%20ATP%20Synthesis
Oxidative
phosphorylation.
electron transport
and chemiosmosis
Glycolysis
ATP
ATP
Inner
Mitochondrial
membrane
ATP
H+
H+

Chemiosmosis and the electron transport
Protein complex
chain
of electron
H+
H+
Cyt c
Intermembrane
space
carriers
Q
I
IV
III
ATP
synthase
II
Inner
mitochondrial
membrane
FADH2
NADH+
FAD+
2 H+ + 1/2 O2
NAD+
ADP +
(Carrying electrons
from, food)
Mitochondrial
matrix
ATP
Pi
H+
Electron transport chain
(H+),
Electron transport and pumping of protons
which create an H+ gradient across the membrane
Figure 9.15
H2O
Chemiosmosis
ATP synthesis powered by the flow
Of H+ back across the membrane
Oxidative phosphorylation
Chemiosmosis

A mechanism which uses energy stored in
the H+ gradient across any membrane to
drive cellular work
 Cellular

work in this case = synthesis of ATP
Utilizes ATP synthase
 the enzyme that actually makes ATP from ADP
and Pi
Chemiosmosis: The EnergyCoupling Mechanism
INTERMEMBRANE SPACE
H+
H+
H+
H+
H+
H+
H+
H+
ATP Synthase
Figure 9.14
ADP
+
Pi
MITOCHONDRIAL MATRIX
ATP
Electron shuttles
span membrane
CYTOSOL
MITOCHONDRION
2 NADH
or
2 FADH2
2 NADH
2 NADH

6 NADH
2 FADH2
There are three main processes inOxidative
this
phosphorylation:
metabolic enterprise
electron transport
Glycolysis
Glucose
2
Pyruvate
+ 2 ATP
by substrate-level
phosphorylation
Maximum per
glucose:
2
Acetyl
CoA
Citric
acid
cycle
+ 2 ATP
by substrate-level
phosphorylation
About
36 or 38 ATP
and
chemiosmosis
+ about 32 or 34 ATP
by oxidative
phosphorylation

We will cover the following two slides
when we learn about photosynthesis, but
you can preview them now if you want.
You’ll probably understand most of them!
A Comparison of Chemiosmosis
in Chloroplasts and
Mitochondria
 Chloroplasts
and mitochondria
ATP by the SAME
basic mechanism:
chemiosmosis
But use different sources of
energy to accomplish this
Generate

http://student.ccbcmd.edu/~gkaiser/biotutorials/cellresp/atp
ase_flash.html

The spatial
organization of
chemiosmosis
differs in
chloroplasts and
mitochondria

In both organelles
 electron
transport
chains generate a
H+ gradient across a
membrane

ATP synthase
 Uses
this protonmotive force to
make ATP