Chapter 4
Cells and Energy
Cellular Respiration
Cellular respiration
 Process by which food molecules are
broken down to release energy
 Glucose and other 6-carbon sugars are
major sources of energy
 Aerobic processes require oxygen
 Anaerobic processes don’t need oxygen
Releasing energy with O2
 process involves 4 steps




Glycolysis
Converting pyruvic acid to acetic acid
Citric acid cycle (Kreb’s cycle)
Electron transport chain
Glycolysis
 6-carbon glucose breaks down to 2
molecules of pyruvic acid (each with 3carbons)
 No oxygen required
 Also produces 2H+ ions and 2electrons
that are picked up by 2NAD+
 Uses 2ATP and produces 4ATP (net
production of 2ATP)
 Occurs in cytoplasm
Glycolysis
4ATP
2ATP
Glucose
2ADP
4ADP + 4P
2PGAL
2 Pyruvic
acid
2NAD+
2NADH + 2H+
Fermentation
 Lactic Acid


Pyruvic acid from glycolysis is converted to
lactic acid
NADH + H+ is recycled to NAD+
 Alcoholic


Pyruvic acid from glycolysis is converted to
ethyl alcohol and carbon dioxide
NADH + H+ is recycled to NAD+
Fermentation
 Lactic acid fermentation occurs in
cytoplasm of muscle cells (causes
muscle soreness)
 Alcoholic fermentation occurs in bacteria
and yeast
 Both forms occur in the cytoplasm
WITHOUT oxygen
Pyruvic acid to acetic acid
 2 Pyruvic acids moves from the
cytoplasm into the mitochondria
 Each pyruvic acid loses a C to CO2 to
make acetic acid
 2 Acetic acids are combined with
coenzyme A to make 2 acetyl-CoA
 2H+ and 2 electrons are picked up by
NAD+
Pyruvic Acid
Mitochondrial
membrane
Outside the
mitochondrion
Pyruvic
acid
CO2
Inside the
mitochondrion
Pyruvic
acid
Coenzyme A
Intermediate
by-product NAD+
- CoA
Acetyl-CoA
NADH + H+
Citric acid cycle (Kreb’s cycle)
 Each acetyl-CoA enters the cycle and
combines with the 4-carbon oxaloacetic
acid to make citric acid
 Citric acid loses a C to CO2 and releases
H+ to NAD+ to become ketoglutaric acid
 Ketoglutaric acid loses a C to CO2,
stores energy in an ATP and releases
H+ and electrons to NAD+ to make
succinic acid
Kreb’s continued
 Succinic acid releases H+ and electrons
to NAD+ and FAD and converted back to
oxaloacetic acid
 Products of Kreb’s cycle




4 CO2
2 ATP
6 NADH + H+
2 FADH
The Citric
Acid Cycle
(Acetyl-CoA)
NADH +
H+
NAD+
The
mitochondria
host the citric
acid cycle.
Oxaloacetic acid
Citric acid
NAD+
NADH + H+
O=
=O
(CO2)
Citric
Acid
Cycle
NAD+
NADH + H+
O=
=O
ADP +
ATP
FADH2 FAD
(CO2)
Electron Transport Chain
 All NADH + H+ and FADH produced go
to the electron transport chain
 Each NADH + H+ produces 3 ATP (30
ATP)
 Each FADH produces 2 ATP (4 ATP)
 Electron transport chain produces a total
of 34 ATP
The electron transport chain
Electron carrier
proteins
Space between
inner and outer
membranes
Enzyme
Inner membrane
e-
Electron
pathway
NADH
NAD+
FADH2
FAD
4H+ + O2
+ 4 electrons
H2O
ADP +
H2O
ATP
Center of
mitochondrion
Total ATP production
 Net ATP in glycolysis is 2
 ATP production in Kreb’s is 2
 ATP production in ETC is 34
 Total = 38 ATP