NADH
e–
NADH
e–
e–
e–
Cytoplasm
e–
NADH and
FADH 2
e–
Glycolysis
glucose
Mitochondrion
e–
Citric acid
cycle
Preparatory reaction
pyruvate
Electron transport
chain and
chemiosmosis
2 ADP
2 ADP
4 ATP total
4 ADP
2
ATP
net gain
2 ADP
2
ATP
32 ADP
or 34
32
or 34
ATP
CELLULAR RESPIRATION
Chapter 1
Outline

Cellular Respiration

Phases of Cellular Respiration

Glycolysis

Preparatory Reaction

Citric Acid Cycle

Electron Transport System

Fermentation
Overview


Living cells require energy from outside sources
Some animals, such as the giant panda, obtain
energy by eating plants, and some animals feed on
other organisms that eat plants
How do these leaves power the work of life for the giant panda?
Light
energy
ECOSYSTEM
Photosynthesis
in chloroplasts
CO2 + H2O
Cellular respiration
in mitochondria
ATP
ATP powers most cellular work
Heat
energy
Organic
+
molecules
O2
Cellular Respiration


A cellular process that breaks down
carbohydrates and other metabolites with the
connected buildup of ATP
Breakdown of organic molecules is exergonic
Other metabolites? i.e.
H2O
O2 and glucose enter cells,
which release H2O and CO2.
CO2
intermembrane
space
cristae
Mitochondria use
energy from
glucose to form ATP
from ADP + P .
ADP +
P
ATP
Cellular Respiration: Processes

Several processes are central to cellular
respiration and related pathways
 Aerobic
respiration consumes organic molecules
and O2 and yields ATP
 Anaerobic
respiration is similar to aerobic
respiration but consumes compounds other than O2
 Fermentation
is a partial degradation of sugars
that occurs without necessary usage of O2
Cellular Respiration: Processes

Most prevalent and efficient is aerobic process.
C6H12O6 + 6 O2  6 CO2 + 6 H2O + Energy (ATP + heat)

Energy extracted from glucose molecule:



Released step-wise
Allows ATP to be produced efficiently
Oxidation-reduction enzymes include NAD+ and FAD as
coenzymes
Redox Reactions and Aerobic Cellular
Respiration

Electrons are removed from substrates and received
by oxygen, which combines with H+ to become water.

Glucose is oxidized and O2 is reduced
becomes oxidized
becomes reduced
Step-wise Energy Harvest:




+
NAD
Step-wise reaction for energy harvest
Electrons from organic compounds are usually first
transferred to NAD+, a coenzyme
As an electron acceptor, NAD+ functions as an
oxidizing agent during cellular respiration
Each NADH (the reduced form of NAD+) represents
stored energy that is tapped to synthesize ATP
Step-wise Energy Harvest:




+
NAD
NADH passes the electrons to the electron transport
chain
Unlike an uncontrolled reaction, the electron transport
chain passes electrons in a series of steps instead of
one explosive reaction
O2 pulls electrons down the chain in an energy-yielding
tumble
The energy yielded is used to regenerate ATP
H2 + 1/2 O2
1/
2H
(from food via NADH)
2 H+ + 2 e–
2 O2
Controlled
release of
energy for
synthesis of
ATP
Explosive
release of
heat and light
energy
1/
(a) Uncontrolled reaction
(b) Cellular respiration
2 O2
Stages of Cellular Respiration

Cellular respiration has four stages:

Glycolysis (breaks down glucose into two molecules of
pyruvate)

Transition (preparatory) (pyruvates are oxidized and enter
mitochondria)

The citric acid cycle (completes the breakdown of glucose)

Oxidative phosphorylation: Electron Transport Chain and
chemiosis (accounts for most of the ATP synthesis)
Electrons carried
via NADH and
FADH2
Electrons
carried
via NADH
Citric
acid
cycle
Glycolysis
Pyruvate
Glucose
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
Mitochondrion
Cytosol
ATP
ATP
ATP
Substrate-level
phosphorylation
Substrate-level
phosphorylation
Oxidative
phosphorylation
STAGE 1:
Glycolysis Pathway: Splitting of Sugars


Glycolysis (“splitting of sugar”) breaks down
glucose into two molecules of pyruvate
Occurs in the cytoplasm and has two major phases:
 Energy
investment phase
 Energy payoff phase
Fig. 9-9-1
Glucose
ATP
1
Hexokinase
ADP
Glucose
Glucose-6-phosphate
ATP
1
Hexokinase
ADP
Glucose-6-phosphate
Fig. 9-9-2
Glucose
ATP
1
Hexokinase
ADP
Glucose-6-phosphate
2
Phosphoglucoisomerase
Fructose-6-phosphate
Glucose-6-phosphate
2
Phosphoglucoisomerase
Fructose-6-phosphate
Fig. 9-9-3
Glucose
ATP
1
Hexokinase
ADP
Fructose-6-phosphate
Glucose-6-phosphate
2
Phosphoglucoisomerase
ATP
3
Phosphofructokinase
Fructose-6-phosphate
ATP
3
Phosphofructokinase
ADP
ADP
Fructose1, 6-bisphosphate
Fructose1, 6-bisphosphate
Fig. 9-9-4
Glucose
ATP
1
Hexokinase
ADP
Glucose-6-phosphate
2
Phosphoglucoisomerase
Fructose-6-phosphate
ATP
Fructose1, 6-bisphosphate
4
Aldolase
3
Phosphofructokinase
ADP
5
Isomerase
Fructose1, 6-bisphosphate
4
Aldolase
5
Isomerase
Dihydroxyacetone
phosphate
Glyceraldehyde3-phosphate
Dihydroxyacetone
phosphate
Glyceraldehyde3-phosphate
Fig. 9-9-5
2 NAD+
2 NADH
+ 2 H+
6
Triose phosphate
dehydrogenase
2 Pi
2 1, 3-Bisphosphoglycerate
Glyceraldehyde3-phosphate
2 NAD+
2 NADH
6
Phosphoglyceraldehyde
dehydrogenase
2Pi
+ 2 H+
2 1, 3-Bisphosphoglycerate
Fig. 9-9-6
2 NAD+
2 NADH
+ 2 H+
6
Triose phosphate
dehydrogenase
2 Pi
2 1, 3-Bisphosphoglycerate
2 ADP
7
Phosphoglycerokinase
2 ATP
2 1, 3-Bisphosphoglycerate
2 ADP
2
3-Phosphoglycerate
2 ATP
2
7
Phosphoglycerokinase
3-Phosphoglycerate
Fig. 9-9-7
2 NAD+
2 NADH
+ 2 H+
6
Triose phosphate
dehydrogenase
2Pi
2 1, 3-Bisphosphoglycerate
2 ADP
7 Phosphoglycerokinase
2 ATP
2
3-Phosphoglycerate
8
2
3-Phosphoglycerate
Phosphoglyceromutase
2
8
Phosphoglyceromutase
2-Phosphoglycerate
2
2-Phosphoglycerate
Fig. 9-9-8
2 NAD+
2 NADH
+ 2 H+
6
Triose phosphate
dehydrogenase
2 Pi
2 1, 3-Bisphosphoglycerate
2 ADP
7 Phosphoglycerokinase
2 ATP
2
3-Phosphoglycerate
2
2-Phosphoglycerate
8
Phosphoglyceromutase
2
9
2 H2O
2-Phosphoglycerate
Enolase
9
2 H2 O
2
Enolase
Phosphoenolpyruvate
2
Phosphoenolpyruvate
Fig. 9-9-9
2 NAD+
6
Triose phosphate
dehydrogenase
2 Pi
2 NADH
+ 2 H+
2 1, 3-Bisphosphoglycerate
2 ADP
7 Phosphoglycerokinase
2 ATP
2
Phosphoenolpyruvate
2 ADP
2
3-Phosphoglycerate
8
10
Pyruvate kinase
Phosphoglyceromutase
2 ATP
2
2-Phosphoglycerate
9
2 H2 O
Enolase
2 Phosphoenolpyruvate
2 ADP
10
Pyruvate kinase
2 ATP
2
2
Pyruvate
Pyruvate
Glycolysis Pathway: Summary
Energy investment phase
Glucose
2 ADP + 2 P
2 ATP
used
4 ATP
formed
Energy payoff phase
4 ADP + 4 P
2 NAD+ + 4 e– + 4 H+
2 NADH + 2 H+
2 Pyruvate + 2 H2O
Net
Glucose
4 ATP formed – 2 ATP used
2 NAD+ + 4 e– + 4 H+
2 Pyruvate + 2 H2O
2 ATP
2 NADH + 2 H+
Glycolysis: Inputs and Outputs
Glycolysis
inputs
outputs
glucose
2 pyruvate
2 NADH
2 NAD+
2
ATP
2 ADP
4 ADP + 4 P
4 ATP total
2
ATP
net gain
27
Pyruvate


is a pivotal metabolite in cellular respiration
If O2 is not available to the cell, fermentation, an
anaerobic process, occurs in the cytoplasm.
 During
fermentation, glucose is incompletely
metabolized to lactate, or to CO2 and alcohol
(depending on the organism).

If O2 is available to the cell, pyruvate enters
mitochondria by aerobic process.
STAGE 2:
Transition (Preparatory) Stage



Connects glycolysis to the citric acid cycle
End product of glycolysis, pyruvate, enters the
mitochondrial matrix
Pyruvate converted to 2-carbon acetyl CoA

Attached to Coenzyme A to form acetyl-CoA

Electron picked up (as hydrogen atom) by NAD+

CO2 released, and transported out of mitochondria into the
cytoplasm
CYTOSOL
MITOCHONDRION
NAD+
NADH
+ H+
2
1
Pyruvate
Transport protein
3
CO2
Coenzyme A
Acetyl CoA
STAGE 3: Citric Acid Cycle/ Krebs Cycle
Pyruvate
CO2
NAD+
CoA
NADH
+ H+
Acetyl CoA
CoA
CoA
Citric
acid
cycle
2 CO2
FADH2
3 NAD+
3 NADH
FAD
+ 3 H+
ADP + P
ATP
i

Occurs in the mitochondria
Fig. 9-12-2
Acetyl CoA
CoA—SH
H2O
1
Oxaloacetate
2
Citrate
Isocitrate
Citric
acid
cycle
Fig. 9-12-3
Acetyl CoA
CoA—SH
1
H2O
Oxaloacetate
2
Citrate
Isocitrate
NAD+
Citric
acid
cycle
3
NADH
+ H+
CO2
-Ketoglutarate
Fig. 9-12-4
Acetyl CoA
CoA—SH
1
H2O
Oxaloacetate
2
Citrate
Isocitrate
NAD+
Citric
acid
cycle
NADH
+ H+
3
CO2
CoA—SH
-Ketoglutarate
4
NAD+
Succinyl
CoA
NADH
+ H+
CO2
Fig. 9-12-5
Acetyl CoA
CoA—SH
1
H2O
Oxaloacetate
2
Citrate
Isocitrate
NAD+
Citric
acid
cycle
NADH
+ H+
3
CO2
CoA—SH
-Ketoglutarate
4
CoA—SH
5
NAD+
Succinate
Pi
GTP GDP
ADP
ATP
Succinyl
CoA
NADH
+ H+
CO2
Fig. 9-12-6
Acetyl CoA
CoA—SH
H2O
1
Oxaloacetate
2
Citrate
Isocitrate
NAD+
Citric
acid
cycle
Fumarate
NADH
+ H+
3
CO2
CoA—SH
6
-Ketoglutarate
4
CoA—SH
5
FADH2
NAD+
FAD
Succinate
Pi
GTP GDP
ADP
ATP
Succinyl
CoA
NADH
+ H+
CO2
Fig. 9-12-7
Acetyl CoA
CoA—SH
H2O
1
Oxaloacetate
2
Malate
Citrate
Isocitrate
NAD+
H2O
Citric
acid
cycle
7
Fumarate
NADH
+ H+
3
CO2
CoA—SH
6
-Ketoglutarate
4
CoA—SH
5
FADH2
NAD+
FAD
Succinate
Pi
GTP GDP
ADP
ATP
Succinyl
CoA
NADH
+ H+
CO2
Fig. 9-12-8
Acetyl CoA
CoA—SH
NADH
+H+
H2O
1
NAD+
8
Oxaloacetate
2
Malate
Citrate
Isocitrate
NAD+
H2O
Citric
acid
cycle
7
Fumarate
NADH
+ H+
3
CO2
CoA—SH
6
-Ketoglutarate
4
CoA—SH
5
FADH2
NAD+
FAD
Succinate
Pi
GTP GDP
ADP
ATP
Succinyl
CoA
NADH
+ H+
CO2
Citric Acid Cycle: Balance Sheet
Citric acid cycle
inputs
outputs
2 acetyl groups
6 NAD+
2 FAD
4 CO2
6 NADH
2 ADP + 2
P
2 FADH2
2
ATP
39
STAGE 4: The Electron Transport Chain




Occurs in the cristae of mitrochondrion
Most of the chain’s components are proteins, which
exist in multiprotein complexes
The carriers alternate reduced and oxidized states
as they accept and donate electrons
Electrons drop in free energy as they go down the
chain and are finally passed to O2, forming H2O
STAGE 4: The Electron Transport Chain

Series of carrier molecules:
Pass energy rich electrons successively from one to another
 Complex arrays of protein and cytochromes






Cytochromes are respiratory molecules
Complex carbon rings with metal atoms in center
Receives electrons from NADH & FADH2
Produce ATP by chemiosis (proton pumps and ATP
Synthase)
Oxygen serves as a final electron acceptor

Oxygen ion combines with hydrogen ions to form water
H+
H+
H+
Protein complex
of electron
carriers
H+
Cyt c
V
Q



FADH2
NADH
ATP
synthase
FAD
2 H+ + 1/2O2
NAD+
H2O
ADP + P i
(carrying electrons
from food)
ATP
H+
1 Electron transport chain
Oxidative phosphorylation
2 Chemiosmosis
Cellular Respiration: Summary
Cellular Respiration Energy Summary:
Aerobic

In general the flow would be as such for ATP
production:
 NADH  electron transport chain 
proton-motive force  ATP
 glucose

About 40% of the energy in a glucose molecule is
transferred to ATP during cellular respiration,
making about 38 ATP
 HIGH!
Cellular Respiration:
Anaerobic and Fermentative
•



Glycolysis can produce ATP with or without O2 (in aerobic
or anaerobic conditions)
In the absence of O2, glycolysis couples with fermentation
or anaerobic respiration to produce ATP
Anaerobic respiration uses an electron transport chain with
an electron acceptor other than O2, for example sulfate
Fermentation uses phosphorylation instead of an electron
transport chain to generate ATP
Fig. 9-18a
2 ADP + 2 P
Glucose
i
2 ATP
Glycolysis
2 Pyruvate
2 NAD+
2 Ethanol
(a) Alcohol fermentation
2 NADH
+ 2 H+
2 CO2
2 Acetaldehyde
Fig. 9-18b
2 ADP + 2 P
Glucose
i
2 ATP
Glycolysis
2 NAD+
2 Lactate
(b) Lactic acid fermentation
2 NADH
+ 2 H+
2 Pyruvate
Fermentation and Aerobic Respiration
Compared



Both processes use glycolysis to oxidize glucose and
other organic fuels to pyruvate
The processes have different final electron acceptors:
an organic molecule (such as pyruvate or
acetaldehyde) in fermentation and O2 in cellular
respiration
Cellular respiration produces 38 ATP per glucose
molecule; fermentation produces 2 ATP per glucose
molecule
Efficiency of Fermentation
Fermentation
inputs
outputs
glucose
2 ADP + 2
2 lactate or
2 alcohol and 2 CO2
P
2
ATP
net gain
49
Fermentation and Aerobic Respiration
Compared



Obligate anaerobes carry out fermentation or
anaerobic respiration and cannot survive in the
presence of O2
Yeast and many bacteria are facultative anaerobes,
meaning that they can survive using either
fermentation or cellular respiration
In a facultative anaerobe, pyruvate is a fork in the
metabolic road that leads to two alternative catabolic
routes
Fig. 9-19
Glucose
CYTOSOL
Glycolysis
Pyruvate
No O2 present:
Fermentation
O2 present:
Aerobic cellular
respiration
MITOCHONDRION
Ethanol
or
lactate
Acetyl CoA
Citric
acid
cycle
Fermentation: Pros and Cons

Advantages
 Provides
a quick burst of ATP energy for
muscular activity.

Disadvantages
 Lactate
is toxic to cells.
 Lactate changes pH and causes muscles to
fatigue.
 Oxygen debt and cramping
Products of Fermentation
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
© The McGraw Hill Companies, Inc./Bruce M. Johnson, photographer
53
Products of Fermentation
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
© The McGraw Hill Companies, Inc./Bruce M. Johnson, photographer
54
Products of Fermentation
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
© The McGraw Hill Companies, Inc./Bruce M. Johnson, photographer
55
Review
1.
2.
4.
5.
6.
Name the four stages of cellular respiration; for
each, state the region of the eukaryotic cell where it
occurs and the products that result
In general terms, explain the role of the electron
transport chain in cellular respiration
Explain where and how the respiratory electron
transport chain creates a proton gradient for 3 ATP
production
Distinguish between fermentation and anaerobic
respiration
Distinguish between obligate and facultative
anaerobes
Mitochondria and Alternative Energy
Sources
Petite mutants of yeast have defective
mitochondria incapable of oxidative
phosphorylation. What carbon sources
can these mutants use to grow?
a.
b.
c.
d.
e.
Glucose
fatty acids
Pyruvate
all of the above
none of the above
Glycolysis
To sustain high rates of glycolysis under
anaerobic conditions, cells require
a.
b.
c.
d.
e.
functioning mitochondria.
Oxygen.
oxidative phosphorylation of ATP.
NAD+.
All of the above are correct.
Electron Transport Chain and
Respiration 1
Rotenone inhibits complex I (NADH dehydrogenase). When
complex I is completely inhibited, cells will
a.
b.
c.
d.
neither consume oxygen nor
make ATP.
not consume oxygen and will
make ATP through glycolysis
and fermentation.
not consume oxygen and will
make ATP only through
substrate-level phosphorylation.
consume less oxygen but still
make some ATP through both
glycolysis and respiration.
Catabolism and
Anaerobiosis
During intense exercise,
as muscles go into
anaerobiosis,
the body will increase
its consumption of
a.
b.
c.
d.
fats.
proteins.
carbohydrates.
all of the above
Evolution of Metabolic Pathways
Glycolysis is found in all domains of life and is therefore
believed to be ancient in origin. What can be said about the
origin of the citric acid cycle, the electron transport chain, and
the F1 ATPase?
a.
b.
c.
d.
They evolved after photosynthesis generated free
oxygen.
They evolved before photosynthesis and used electron
acceptors other than oxygen.
Individual enzymes were present before photosynthesis
but served other functions, such as amino acid
metabolism.
They evolved when the ancestral eukaryotes acquired
mitochondria.