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Chapter 9
Cellular Respiration:
Harvesting Chemical Energy
PowerPoint Lectures for
Biology, Seventh Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Overview: Life Is Work
• Living cells
– Require transfusions of energy from outside
sources to perform their many tasks
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1. Why do animals eat and breath?
–
Cells require ______________ and
_______________ for growth, development,
maintenance and repair
2. From what kind of food molecules does the energy
come from?
3. What in these compounds provides the energy for
cellular work?
4. Can this energy be used directly by cells?
5. From what kind of molecules can this energy be
used directly?
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6. How is ATP produced from the breakdown of
sugars?
•
What is this process called?
7. What’s needed for this process to occur?
8. What is the net equation for this process
under aerobic conditions?
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• The giant panda
– Obtains energy for its cells by eating plants
Figure 9.1
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• Energy
– Flows into an ecosystem as sunlight and
leaves as heat
Light energy
ECOSYSTEM
Photosynthesis
in chloroplasts
Organic
CO2 + H2O
+ O2
Cellular
molecules
respiration
in mitochondria
ATP
powers most cellular work
Figure 9.2
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Heat
energy
• Concept 9.1: Catabolic pathways yield energy
by oxidizing organic fuels
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Catabolic Pathways and Production of ATP
• The breakdown of organic molecules is
exergonic
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• One catabolic process, fermentation
– Is a partial degradation of sugars that occurs
without oxygen
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• Cellular respiration
– Is the most prevalent and efficient catabolic
pathway
– Consumes oxygen and organic molecules
such as glucose
– Yields ATP
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• To keep working
– Cells must regenerate ATP
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Redox Reactions: Oxidation and Reduction
• Catabolic pathways yield energy
– Due to the transfer of electrons
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The Principle of Redox
• Redox reactions
– Transfer electrons from one reactant to
another by oxidation and reduction
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• In oxidation
– A substance loses electrons, or is oxidized
• In reduction
– A substance gains electrons, or is reduced
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• Examples of redox reactions
becomes oxidized
(loses electron)
Na
+
Cl
Na+
+
becomes reduced
(gains electron)
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Cl–
• Some redox reactions
– Do not completely exchange electrons
– Change the degree of electron sharing in
covalent bonds
Products
Reactants
becomes oxidized
+
CH4
CO
2O2
+
Energy
2 H2O
becomes reduced
O
O
C
O
H
O
O
H
H
H
C
+
2
H
H
Methane
(reducing
agent)
Oxygen
(oxidizing
agent)
Figure 9.3
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Carbon dioxide
Water
Oxidation of Organic Fuel Molecules During
Cellular Respiration
• During cellular respiration
– Glucose is oxidized and oxygen is reduced
becomes oxidized
C6H12O6 + 6O2
6CO2 + 6H2O + Energy
becomes reduced
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Stepwise Energy Harvest via NAD+ and the Electron
Transport Chain
• Cellular respiration
– Oxidizes glucose in a series of steps
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• Electrons from organic compounds
– Are usually first transferred to NAD+, a
coenzyme
2 e– + 2 H+
NAD+
Dehydrogenase
O
NH2
H
C
CH2
O
O–
O
O P
O
H
–
O P O HO
O
N+ Nicotinamide
(oxidized form)
H
OH
HO
CH2
N
H
O
H
HO
N
H
OH
Reduction of NAD+
+ 2[H]
(from food) Oxidation of NADH
NH2
N
N
2 e– + H+
H
Figure 9.4
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NADH
H O
C
H
N
NH2
Nicotinamide
(reduced form)
+
• NADH, the reduced form of NAD+
– Passes the electrons to the electron transport
chain
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• If electron transfer is not stepwise
– A large release of energy occurs
– As in the reaction of hydrogen and oxygen to
form water
Free energy, G
H2 + 1/2 O2
Figure 9.5 A
Explosive
release of
heat and light
energy
H2O
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(a) Uncontrolled reaction
• The electron transport chain
– Passes electrons in a series of steps instead of
in one explosive reaction
– Uses the energy from the electron transfer to
form ATP
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2H
1/
+
2
O2
1/
O2
(from food via NADH)
Free energy, G
2 H+ + 2 e–
Controlled
release of
energy for
synthesis of
ATP
ATP
ATP
ATP
2 e–
2
H+
H2O
Figure 9.5 B
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(b) Cellular respiration
2
The Stages of Cellular Respiration: A Preview
• Respiration is a cumulative function of three
metabolic stages
– Glycolysis
– The citric acid cycle
– Oxidative phosphorylation
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• Glycolysis
– Breaks down glucose into two molecules of
pyruvate
• The citric acid cycle
– Completes the breakdown of glucose
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• Oxidative phosphorylation
– Is driven by the electron transport chain
– Generates ATP
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• An overview of cellular respiration
Electrons carried
via NADH and
FADH2
Electrons
carried
via NADH
Citric
acid
cycle
Glycolsis
Pyruvate
Glucose
Cytosol
Mitochondrion
ATP
Figure 9.6
Oxidative
phosphorylation:
electron
transport and
chemiosmosis
Substrate-level
phosphorylation
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ATP
Substrate-level
phosphorylation
ATP
Oxidative
phosphorylation
• Both glycolysis and the citric acid cycle
– Can generate ATP by substrate-level
phosphorylation
Enzyme
Enzyme
ADP
P
Substrate
+
Figure 9.7
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Product
ATP
• Concept 9.2: Glycolysis harvests energy by
oxidizing glucose to pyruvate
• Glycolysis
– Means “splitting of sugar”
– Breaks down glucose into pyruvate
– Occurs in the cytoplasm of the cell
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• Glycolysis consists of two major phases
– Energy investment phase
– Energy payoff phase
Citric
acid
cycle
Glycolysis
Oxidative
phosphorylation
ATP
ATP
ATP
Energy investment phase
Glucose
2 ATP + 2 P
2 ATP
used
Energy payoff phase
4 ADP + 4 P
2 NAD+ + 4 e- + 4 H
+
4 ATP formed
2 NADH + 2 H+
2 Pyruvate + 2 H2O
Glucose
4 ATP formed – 2 ATP used
Figure 9.8
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2 NAD+ + 4 e– + 4 H
+
2 Pyruvate + 2 H2O
2 ATP + 2 H+
2 NADH
• A closer look at the energy investment phase
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CH2OH
HH
H
HO H
HO
OH
H OH
Glycolysis
Glucose
ATP
1
Hexokinase
ADP
CH2OH P
HH OH
OH H
HO
H OH
Glucose-6-phosphate
2
Phosphoglucoisomerase
CH2O P
O CH2OH
H HO
HO
H
HO H
Fructose-6-phosphate
ATP
3
Phosphofructokinase
ADP
P O CH2 O CH2 O P
HO
H
OH
HO H
Fructose1, 6-bisphosphate
4
Aldolase
5
H
P O CH2 Isomerase
C O
C O
CHOH
CH2OH
CH2 O P
Figure 9.9 A
Dihydroxyacetone
phosphate
Glyceraldehyde3-phosphate
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Citric
Oxidative
acid
cycle phosphorylation
• A closer look at the energy payoff phase
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6
Triose phosphate
dehydrogenase
2 NAD+
2 Pi
2 NADH
+ 2 H+
2
P
O C O
CHOH
CH2 O P
1, 3-Bisphosphoglycerate
2 ADP
7
Phosphoglycerokinase
2 ATP
O–
2
C
CHOH
CH2 O P
3-Phosphoglycerate
8
Phosphoglyceromutase
2
O–
C
O
H C O
P
CH2OH
2-Phosphoglycerate
9
Enolase
2H O
2
2
O–
C O
C O
P
CH2
Phosphoenolpyruvate
2 ADP
10
Pyruvate kinase
2 ATP
2
O–
C O
C O
Figure 9.8 B
CH3
Pyruvate
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• Concept 9.3: The citric acid cycle completes
the energy-yielding oxidation of organic
molecules
• The citric acid cycle
– Takes place in the matrix of the mitochondrion
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• Before the citric acid cycle can begin
– Pyruvate must first be converted to acetyl CoA,
which links the cycle to glycolysis
CYTOSOL
MITOCHONDRION
NAD+
NADH
+ H+
O–
S
CoA
C
O
2
C
C
O
O
1
3
CH3
Pyruvate
Transport protein
Figure 9.10
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CH3
Acetyle CoA
CO2
Coenzyme A
• An overview of the citric acid cycle
Pyruvate
(from glycolysis,
2 molecules per glucose)
Glycolysis
Citric
acid
cycle
ATP
ATP
Oxidative
phosphorylatio
n
ATP
CO2
CoA
NADH
+ 3 H+ Acetyle CoA
CoA
CoA
Citric
acid
cycle
2 CO2
3 NAD+
FADH2
FAD
3 NADH
+ 3 H+
ADP + P i
ATP
Figure 9.11
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• A closer look at the citric acid cycle
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Glycolysis
Citric
Oxidative
acid phosphorylation
cycle
S
CoA
C
O
CH3
Acetyl CoA
CoA SH
O
NADH
+ H+
C COO–
COO–
1
CH2
COO–
NAD+
8 Oxaloacetate
HO C
COO–
COO–
CH2
COO–
HO CH
H2O
CH2
CH2
2
HC COO–
COO–
Malate
Figure
CH2
HO
Citrate
9.12
COO–
Isocitrate
COO–
H2O
COO–
CH
CO2
Citric
acid
cycle
7
3
NAD+
COO–
Fumarate
HC
CH
CH2
CoA SH
6
CoA SH
COO–
FAD
CH2
CH2
COO–
C O
Succinate
Pi
S
CoA
GTP GDP Succinyl
CoA
ADP
ATP
Figure 9.12
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4
C O
COO–
CH2
5
CH2
FADH2
COO–
NAD+
NADH
+ H+
+ H+
a-Ketoglutarate
CH2
COO–
NADH
CO2
• Concept 9.4: During oxidative phosphorylation,
chemiosmosis couples electron transport to
ATP synthesis
• NADH and FADH2
– Donate electrons to the electron transport
chain, which powers ATP synthesis via
oxidative phosphorylation
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The Pathway of Electron Transport
• In the electron transport chain
– Electrons from NADH and FADH2 lose energy
in several steps
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• At the end of the chain
– Electrons are passed to oxygen, forming water
NADH
50
Free energy (G) relative to O2 (kcl/mol)
FADH2
40
FMN
I
Fe•S
Fe•S II
O
30
Multiprotein
complexes
FAD
III
Cyt b
Fe•S
20
Cyt c1
IV
Cyt c
Cyt a
Cyt a3
10
0
Figure 9.13
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2 H + + 12 O2
H2 O
Chemiosmosis: The Energy-Coupling Mechanism
• ATP synthase
– Is the enzyme that actually makes ATP
INTERMEMBRANE SPACE
H+
H+
H+
H+
H+
H+
H+
A rotor within the
membrane spins
clockwise when
H+ flows past
it down the H+
gradient.
A stator anchored
in the membrane
holds the knob
stationary.
H+
ADP
+
Pi
Figure 9.14
MITOCHONDRIAL MATRIX
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ATP
A rod (for “stalk”)
extending into
the knob also
spins, activating
catalytic sites in
the knob.
Three catalytic
sites in the
stationary knob
join inorganic
Phosphate to ADP
to make ATP.
• At certain steps along the electron transport
chain
– Electron transfer causes protein complexes to
pump H+ from the mitochondrial matrix to the
intermembrane space
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• The resulting H+ gradient
– Stores energy
– Drives chemiosmosis in ATP synthase
– Is referred to as a proton-motive force
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• Chemiosmosis
– Is an energy-coupling mechanism that uses
energy in the form of a H+ gradient across a
membrane to drive cellular work
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• Chemiosmosis and the electron transport chain
Oxidative
phosphorylation.
electron transport
and chemiosmosis
Glycolysis
ATP
Inner
Mitochondrial
membrane
ATP
ATP
H+
H+
H+
Intermembrane
space
Protein complex
of electron
carners
Q
I
Inner
mitochondrial
membrane
IV
III
ATP
synthase
II
FADH2
NADH+
Mitochondrial
matrix
H+
Cyt c
FAD+
NAD+
2 H+ + 1/2 O2
H2O
ADP +
(Carrying electrons
from, food)
ATP
Pi
H+
Chemiosmosis
Electron transport chain
+
ATP
synthesis
powered by the flow
Electron transport and pumping of protons (H ),
+
+
which create an H gradient across the membrane Of H back across the membrane
Figure 9.15
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Oxidative phosphorylation
An Accounting of ATP Production by Cellular
Respiration
• During respiration, most energy flows in this
sequence
– Glucose to NADH to electron transport chain to
proton-motive force to ATP
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• There are three main processes in this
metabolic enterprise
Electron shuttles
span membrane
CYTOSOL
MITOCHONDRION
2 NADH
or
2 FADH2
2 NADH
2 NADH
Glycolysis
Glucose
2
Pyruvate
6 NADH
Citric
acid
cycle
2
Acetyl
CoA
+ 2 ATP
by substrate-level
phosphorylation
Maximum per glucose:
+ 2 ATP
2 FADH2
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
+ about 32 or 34 ATP
by substrate-level by oxidative phosphorylation, depending
on which shuttle transports electrons
phosphorylation
from NADH in cytosol
About
36 or 38 ATP
Figure 9.16
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• About 40% of the energy in a glucose molecule
– Is transferred to ATP during cellular respiration,
making approximately 38 ATP
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• Concept 9.5: Fermentation enables some cells
to produce ATP without the use of oxygen
• Cellular respiration
– Relies on oxygen to produce ATP
• In the absence of oxygen
– Cells can still produce ATP through
fermentation
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• Glycolysis
– Can produce ATP with or without oxygen, in
aerobic or anaerobic conditions
– Couples with fermentation to produce ATP
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Types of Fermentation
• Fermentation consists of
– Glycolysis plus reactions that regenerate
NAD+, which can be reused by glyocolysis
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• In alcohol fermentation
– Pyruvate is converted to ethanol in two steps,
one of which releases CO2
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• During lactic acid fermentation
– Pyruvate is reduced directly to NADH to form
lactate as a waste product
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2 ADP + 2
P1
2 ATP
O–
C O
Glucose
Glycolysis
C O
CH3
2 Pyruvate
2 NADH
2 NAD+
H
2 CO2
H
H C OH
C O
CH3
CH3
2 Ethanol
2 Acetaldehyde
(a) Alcohol fermentation
2 ADP + 2
Glucose
P1
2 ATP
Glycolysis
O–
C O
C O
O
2 NAD+
2 NADH
C O
H
C OH
CH3
2 Lactate
Figure 9.17
(b) Lactic acid fermentation
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CH3
Fermentation and Cellular Respiration Compared
• Both fermentation and cellular respiration
– Use glycolysis to oxidize glucose and other
organic fuels to pyruvate
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• Fermentation and cellular respiration
– Differ in their final electron acceptor
• Cellular respiration
– Produces more ATP
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• Pyruvate is a key juncture in catabolism
Glucose
CYTOSOL
Pyruvate
No O2 present
Fermentation
O2 present
Cellular respiration
MITOCHONDRION
Ethanol
or
lactate
Figure 9.18
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Acetyl CoA
Citric
acid
cycle
The Evolutionary Significance of Glycolysis
• Glycolysis
– Occurs in nearly all organisms
– Probably evolved in ancient prokaryotes before
there was oxygen in the atmosphere
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• Concept 9.6: Glycolysis and the citric acid
cycle connect to many other metabolic
pathways
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The Versatility of Catabolism
• Catabolic pathways
– Funnel electrons from many kinds of organic
molecules into cellular respiration
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• The catabolism of various molecules from food
Proteins
Carbohydrates
Amino
acids
Sugars
Fats
Glycerol
Glycolysis
Glucose
Glyceraldehyde-3- P
NH3
Pyruvate
Acetyl CoA
Citric
acid
cycle
Figure 9.19
Oxidative
phosphorylation
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Fatty
acids
Biosynthesis (Anabolic Pathways)
• The body
– Uses small molecules to build other
substances
• These small molecules
– May come directly from food or through
glycolysis or the citric acid cycle
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Regulation of Cellular Respiration via Feedback
Mechanisms
• Cellular respiration
– Is controlled by allosteric enzymes at key
points in glycolysis and the citric acid cycle
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• The control of cellular respiration
Glucose
Glycolysis
Fructose-6-phosphate
–
Inhibits
AMP
Stimulates
+
Phosphofructokinase
–
Fructose-1,6-bisphosphate
Inhibits
Pyruvate
Citrate
ATP
Acetyl CoA
Citric
acid
cycle
Figure 9.20
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Oxidative
phosphorylation
-
Superoxide radical, O2 , formation
•
O2
-
•
O2
-
generated constantly as part of normal aerobic life
formed in mitochondria when O2 is reduced along the electron transport chain
Oxygen Free Radical Theory of Aging
• E.T.C.  Superoxide Radical, O2-  SOD
(superoxide dismutase) converts O2- to
hydrogen peroxide, H2O2  Catalase
converts H2O2 to water and O2
OR
• H2O2 moves to the nucleus of the cell 
H2O2 reacts with Fe2+  produces hydroxyl
radical  Damages DNA and most
everything around it
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Oxygen Free Radical Theory of Aging
• Oxygen is slowly killing us!
• Raj Sohal’s (Southern Methodist University)
– Has doubled or tripled the life span of house
flies if he restricts there movement and hence
the amount of oxygen they consume.
– Gene therapy can be used to increase
longevity by introducing genes that encode the
enzymes the SOD (superoxide dismutase) and
Catalase.
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Oxygen Free Radical Theory of Aging
1. Vitamins C (water-soluble) and E (fatsoluble) are vitamins that deactivate free
radicals.
2. Why is it most beneficial to take both of
them, rather than just one or the other?
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Oxygen Free Radical Theory of Aging
• SOD and catalase levels increase when humans
exercise, thus protecting us from the extra free
radicals produced as a consequence of increased
oxygen consumption.
• House flies do not have the genes to produce
SOD and catalase consequences?
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Glucose Cross-linking with Proteins
•
•
Diabetics
–
Higher than normal blood levels of glucose.
–
Causes diabetics to age ~one-third faster
Cross-linking makes proteins less flexible
–
makes body parts less flexible and stiffer
–
major cause of aging in many tissues:
•
skin, bones, lungs, eyes, joints, and blood
vessels.
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