Chapter 9 (Pages 220-232)
The Powerhouse
Overview of Cellular Respiration
Electrons carried in NADH
Pyruvic
acid
Glucose
Electrons carried
in NADH and
FADH2
Glycolysis
Cytoplasm
Mitochondrion
Copyright Pearson
Prentice Hall
The equation…
OMG!
It’s
flipped!
Literally means “
”
in cellular respiration
 Occurs in the cytosol/cytoplasm
 Process in which 1 molecule of glucose is
broken in half, producing two molecules of
pyruvic acid

2
ATP
2
ADP
P
C
C
C
P
4
ADP
4
ATP
C
C
C
PYRUVATE
(pyruvic acid)
glucose
P
C
C
C
P
2
NAD+
2
NADH
C
C
C
 Requires
2 ATP, but produces 4
ATP  net gain of 2 ATP for the cell
 NAD+
given electrons 

 Super fast! Produces thousands of
ATP molecules in just a few
milliseconds
 You only have so many NAD+
available, can’t keep happening
Two options – all depends on presence O2!
Glycolysis
With O2
Without
O2

Krebs Cycle
 (Citric Acid Cycle)
Fermentation
ETC
(Where most ATP is made)
Anaerobic – follows Glycolysis when oxygen
is not present
 Not how the normal process of CR is
supposed to go! Back-up plan!
 Fermentation releases energy from food
molecules by producing ATP in absence
of O2
 The electrons stored in NADH are
returned to Pyruvic Acid, letting the NAD+
go back to glycolysis and keep making ATP
 Alcoholic fermentation
 Lactic acid fermentation

 Used
by yeasts,
bacteria  why bread
rises
 Converts
sugar into
ethyl alcohol and
CO2
In many cells, the pyruvic
acid that accumulates from
glycolysis can be converted
into lactic acid
 Produced in your body
during rapid exercise
 Causes muscle soreness


The equation for lactic acid fermentation
after glycolysis is:
 Pyruvic acid + NADH → lactic acid + NAD+
In the presence of
oxygen, cellular
respiration proceeds
from glycolysis to the
Krebs Cycle
 Breaks down pyruvic
acid into carbon
dioxide
 Occurs in
mitochondrial matrix

 Discovered
in 1937 by
Hans Krebs - biochemist
 The basic definition of
Krebs Cycle:
 The breaking down of
pyruvic acid into CO2
in a series of energyextracting reactions
Before the cycle starts “turning”
 Step 1  pyruvic acid enters the mitochondria
 Step 2  one carbon molecule from pyruvic
acid breaks off to form CO2
 Step 3  other two carbon atoms tack onto
coenzyme A – this molecule becomes acetyl
coenzyme A
 Step 4  Acetyl CoA adds the two carbon
acetyl group to a 4 carbon molecule…
THIS 6 CARBON MOLECULE IS
CITRIC ACID!
 Step
1  citric
acid loses a
carbon
 That carbon becomes a
CO2 molecule
 NAD+ picks up 2
electrons and H+
 Step
2  the 5carbon molecule
loses a carbon
 That carbon becomes a
CO2 molecule
 NAD+ picks up 2
electrons and a H+
 ATP formed (only 1)
 Step
3  the 4carbon molecule
is ready to start
the cycle again!
 FAD picks up 4
electrons and 2 H+
 NAD picks up one last
set of electrons and
H+
One turn of the Krebs Cycle gives you these
products:
The ETC uses high-energy electrons from the
Krebs cycle to convert ADP into ATP
 In eukaryotes, the ETC is a series of carrier
proteins located in the inner membrane of the
mitochondria
 In prokaryotes, the ETC is in the cell
membrane

2 high energy electrons are transported
through the ETC
 Their energy helps transport H+ through the
membrane

At the end of the ETC
an enzyme (named
Complex IV) is waiting
patiently to snatch up
the electrons and a
couple H+
 The enzyme combines
the electrons, H+, and
O2 
 H+ escape to
intermembrane space

 THEY BUILDIN UP
OVER THERE!!!!!
H+ builds up in the
intermembrane
space, making it
positively
charged
 The H+ rush back to
the negative
membrane side
 As they pass, they
cause ATP
synthase to spin
and make ATP


In the presence of oxygen – 36
total
ATP molecules produced
 38% of the total energy of glucose
 What happened to the remaining 62%?

What can stop this process?
 Carbon monoxide disables Complex IV
 Electron carriers are not recycled
 Cellular respiration cannot continue
 ATP Synthase not as efficient
 Your body turns to fermentation
 When
you need quick energy, how does your
body produce it?
 Lactic Acid Fermentation
 Quick and easy
 When
you need long term energy (longer
than 90 seconds), where do you retrieve
the ATP?
 Cellular Respiration
 Slowwwwwww, but higher amounts
○ Not really, it happens a ton of times every second.
 Muscle stores (carbohydrates), fats