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INTRODUCTION TO CELLULAR RESPIRATION
Chapter 6
Photosynthesis and cellular respiration provide
energy for life
How Cells Harvest Chemical
Energy
•  Cellular respiration makes ATP and consumes O2
–  During the oxidation of glucose to CO2 and
H 2O
Birgit Woelker, PhD
Photosynthesis uses
solar energy to
produce glucose and
O2 from CO2 and H2O
Sunlight energy
Breathing supplies oxygen to our cells and removes
carbon dioxide
ECOSYSTEM
•  Breathing provides for the exchange of O2 and CO2
Photosynthesis in
chloroplasts
Glucose
CO2
+!
+!
H 2O
O2
–  Between an organism and its environment
O2
CO2
Breathing
Cellular respiration in
mitochondria
Cellular respiration
makes ATP and
consumes O2 during the
oxidation of glucose to
CO2 and H2O
Lungs
CO2
ATP
Bloodstream
O2
Muscle cells carrying out
(for cellular work)
Heat energy
Cellular Respiratin
Glucose + O2
CO2 + H2O + ATP
The human body uses energy from ATP for all its
activities
Cellular respiration banks energy in ATP
molecules
•  ATP powers almost all cellular and body activities
•  Cellular respiration breaks down glucose
molecules
–  And banks their energy in ATP
C6H12O6
Glucose
+
6
O2
Oxygen gas
6
CO2
+
Carbon
dioxide
6
H 2O
ATPs
+
Water
Energy
Figure 6.3
Cells tap energy from electrons “falling” from
organic fuels to oxygen
•  Electrons lose potential energy
–  During their transfer from organic
compounds to oxygen
Table 6.4
•  NADH passes electrons to an electron transport chain
•  As electrons “fall” from carrier to carrier and finally to O2
•  Energy is released in small quantities
NAD+
NADH
2
Energy released
and available
for making
2
1
!
2
O2
2 H+
ATP
H 2O
•  When glucose is converted to carbon dioxide
–  It loses hydrogen atoms, which are
added to oxygen, producing water
•  Dehydrogenase removes electrons (in
hydrogen atoms) from fuel molecules
(oxidation)
–  And transfers them to NAD+ (reduction)
H
Loss of hydrogen atoms
(oxidation)
C6H12O6 + 6 O2
6 CO2
Oxidation
H
O
O + 2H
Dehydrogenase
6 H2O + Energy
+
Glucose
(ATP)
Gain of hydrogen atoms
(reduction)
NAD+
+
2H+! +
Figure 6.5A
Reduction
2H
2e-!
NADH
+
H+!
(carries
2 electrons)
Figure 6.5B
Cellular respiration occurs in three main stages
•  Stage 1: Glycolysis
NADH
–  Occurs in the cytoplasm
High-energy electrons
carried by NADH
NADH
FADH2
and
OXIDATIVE
PHOSPHORYLATION
(Electron Transport
and Chemiosmosis)
GLYCOLYSIS
Glucose
CITRIC ACID
CYCLE
Pyruvate
Mitochondrion
Cytoplasm
ATP
Substrate-level
phosphorylation
CO2
ATP
CO2
Substrate-level
phosphorylation
ATP
Oxidative
phosphorylation
–  Breaks down glucose into pyruvate,
producing a small amount of ATP
•  Stage 2: The citric acid cycle
•  Stage 3: Oxidative phosphorylation
–  Takes place in the mitochondria
–  Occurs in the mitochondria
–  Completes the breakdown of glucose,
producing a small amount of ATP
–  Uses the energy released by “falling”
electrons to pump H+ across a
membrane
–  Supplies the third stage of cellular
respiration with electrons
–  Harnesses the energy of the H+ gradient
through chemiosmosis, producing ATP
Glycolysis harvests chemical energy by oxidizing
glucose to pyruvate
•  In glycolysis, ATP is used to prime a glucose
molecule
•  Glycolysis produces ATP by substrate-level
phosphorylation
–  In which a phosphate group is transferred
from an organic molecule to ADP
–  Which is split into two molecules of pyruvate
Enzyme
2
2
NAD+
NADH
+ 2
H+
P
P
P
Adenosine
ADP
Glucose
ATP
2 Pyruvate
2 ADP + 2
Figure 6.7A
P
2
P
Organic molecule
(substrate)
ATP
Figure 6.7B
P
•  In the first phase of glycolysis
•  In the second phase of glycolysis
–  ATP is used to energize a glucose
molecule, which is then split in two
–  ATP, NADH, and pyruvate are formed
P
Step 5 A redox reaction generates
6
9
NADH.
Steps 1 – 3 A fuel molecule is energized,
using ATP.
Glucose
ATP
PREPARATORY PHASE
(energy investment)
Step
1
ADP
NAD
P
+
5
NAD
+H+
P
P
ADP
P 1,3 -Diphosphoglycerate
7
6
ATP
7
P
2
P 3 -Phosphoglycerate
7
P
Fructose-6-phosphate
7
P
P
8
8
2-Phosphoglycerate
ATP
3
P
P
Step 4 A six-carbon intermediate splits
into two three-carbon intermediates.
8
H 2O
ADP
Fructose-1,6-diphosphate
8
H 2O
P
4
P
9
ADP
Phosphoenolpyruvate
(PEP) 9
ADP
9
9
ATP
ATP
Figure 6.7C
Pyruvate
Figure 6.7C
Pyruvate is chemically groomed for the citric acid
cycle
–  Enzymes process pyruvate, releasing CO2
and producing NADH and acetyl CoA
NADH
NAD+
The citric acid cycle completes the oxidation of organic
fuel, generating many NADH and FADH2 molecules
•  In the citric acid cycle
– 
•  Prior to the citric acid cycle
6
P
ADP
6
ATP
Glucose-6-phosphate
ENERGY PAYOFF PHASE
5
P 6 NADH
+H+
P
P
NADH
Steps 6 – 9 ATP and pyruvate
are produced.
Glyceraldehyde-3-phosphate
(G3P)
+
The two-carbon acetyl part of acetyl CoA is
oxidized
Acetyl CoA
CoA
CoA
+ H+!
2
2 CO2
CITRIC ACID CYCLE
CoA
Pyruvate
1
3
CO2
Acetyl CoA
(acetyl coenzyme A)
3
FADH2
3
FAD
Coenzyme A
NAD+
NADH
+!
3 H+
Figure 6.8
Figure 6.9A
ATP
ADP +
P
•  For each turn of the cycle
Most ATP production occurs by oxidative
phosphorylation
–  Two CO2 molecules are released
–  The energy yield is one ATP, three NADH,
and one FADH2
•  Electrons from NADH and FADH2
–  Travel down the electron transport chain
to oxygen, which picks up H+ to form
water
CoA
Acetyl CoA
CoA
2 carbons enter cycle
Oxaloacetate
Citrate
NADH
+ H+!
NAD
CO2
+
CITRIC ACID CYCLE
leaves cycle
Malate
NADH
+!
ADP
FADH2
•  Energy released by the redox reactions
NAD+
+ H+!
–  Is used to pump H+ into the space
between the mitochondrial membranes
P
ATP
Alpha-ketoglutarate
FAD
CO2
leaves cycle
Succinate
1
NADH
Step
Steps
Acetyl CoA stokes the furnace.
NAD+
+ H+!
Steps
and
NADH, ATP, and CO2 are generated
during redox reactions.
Figure 6.9B
and
Redox reactions generate FADH2
and NADH.
H+
•  In chemiosmosis, the
diffuses back through the
inner membrane through ATP synthase complexes
–  Driving the synthesis of ATP
H+
.
H+
H+
Protein
complex
H+
H+
H+
H+
Electron
carrier
Intermembrane space
H+
H+
ATP
synthase
Certain poisons interrupt critical events in cellular
respiration
•  Various poisons
– 
Block the movement of electrons
– 
Block the flow of H+ through ATP synthase
– 
Allow H+ to leak through the membrane
Cyanide,
carbon monoxide
Rotenone
Q+
Cyt c
H+
H+
Inner mitochondrial
membrane
H+
FADH2
H+
H+
H+
ATP
Synthase
FAD
DNP
NAD+
NADH
H
Mitochondrial matrix
H+
H+
H+
Electron
flow
Oligomycin
+
1
2
O2 + 2 H+
H+
FAD
FADH2
H+
H 2O
ADP
+
P
ATP
1 O2
NAD+
NADH
H+
+! 2 H+
2
H+
Electron Transport Chain
H+
Chemiosmosis
H 2O
ADP
+! P
H+
Figure 6.11
Electron Transport Chain
OXIDATIVE PHOSPHORYLATION
Figure 6.10
Chemiosmosis
ATP
Each molecule of glucose yields ~38 molecules of ATP
Fermentation is an anaerobic alternative to
cellular respiration
Electron shuttle
across membrane
Cytoplasm
2 NADH
GLYCOLYSIS
Glucose
•  Under anaerobic conditions, many kinds of cells
Mitochondrion
2 NADH
2 NADH
2
Pyruvate
–  Can use glycolysis alone to produce
small amounts of ATP
(or 2 FADH2)
2 Acetyl
CoA
+ 2 ATP
6 NADH
2 FADH2
OXIDATIVE
PHOSPHORYLATION
(Electron Transport
and Chemiosmosis)
CITRIC ACID
CYCLE
+ about 34 ATP
+ 2 ATP
by substrate-level
phosphorylation
by oxidative phosphorylation
by substrate-level
phosphorylation
Maximum per glucose:
About
38 ATP
•  In alcohol fermentation NADH is oxidized to NAD+
while converting pyruvate to CO2 and ethanol
•  In lactic acid fermentation NADH is
oxidized to NAD+ as pyruvate is
reduced to lactate
2
2
NAD+
2
NADH
NADH
2
NAD+
2 NAD+
2 NADH
2 NADH
2 NAD+
GLYCOLYSIS
2 ADP + 2
Glucose
P
2
ATP
GLYCOLYSIS
2 Pyruvate
2 Lactate
2 ADP + 2 P
Glucose
2 ATP
2 CO2
2 Pyruvate
released
2 Ethanol
INTERCONNECTIONS BETWEEN MOLECULAR
BREAKDOWN AND SYNTHESIS
Cells use many kinds of organic molecules as fuel for
cellular respiration
Food, such as
peanuts
•  Cells use many kinds of organic molecules as
fuel for cellular respiration
•  Carbohydrates,
fats, and
proteins can be
converted to
molecules that
enter glycolysis
or the citric acid
cycle
Carbohydrates
Fats
Sugars
Proteins
Glycerol Fatty acids
Amino acids
Amino
groups
Glucose
G3P
Pyruvate
GLYCOLYSIS
Acetyl
CoA
CITRIC
ACID
CYCLE
OXIDATIVE
PHOSPHORYLATION
(Electron Transport
and Chemiosmosis)
ATP
Food molecules provide raw materials for
biosynthesis
The fuel for respiration ultimately comes from
photosynthesis
ATP needed to drive biosynthesis
ATP
• Cells use some
food molecules
and intermediates
from glycolysis
and the citric acid
cycle as raw
materials
• This process of
biosynthesis
consumes ATP
CITRIC
ACID
CYCLE
•  All organisms
GLUCOSE SYNTHESIS
Acetyl
CoA
Pyruvate
G3P
Glucose
– 
•  Plants, but not animals
– 
Amino
groups
Amino acids
Proteins
Fatty Glycerol
acids
Fats
Cells, tissues, organisms
Sugars
Carbohydrates
Can harvest energy from organic molecules
Can also make these molecules from inorganic
sources by the process of photosynthesis