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Anatomy and Physiology I
Cellular Metabolism
Instructor: Mary Holman
Metabolism
• Refers to all the chemical reactions in
the body that use or release
energy
• It is the energy-balancing between
synthesis reactions and
decomposition reactions in the
body
Anabolism
• a synthesis reaction
• the joining of smaller molecules
to form larger ones
• requires energy
• dehydration synthesis - removal
of water
Formation of a disaccharide:
a molecule of H20 is removed
Fig. 4.1a
CH2OH
CH2OH
O
H
HO
O
H
H
OH
H
H
OH
H
OH
HO
OH
H
H
OH
H20
Monosaccharide
(glucose)
+
H
H
Monosaccharide
(glucose)
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OH
Fig.
4.1b
An example of Anabolism:
A Disaccharide is formed by
dehydration synthesis
CH2OH
CH 2OH
O
H
HO
O
H
H
H
O
OH
H
H
OH
Disaccharide
(maltose)
H
H
+
OH
H
H
OH
H2O
OH
+
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Water
Fig. 4.2a
Dehydration Synthesis of a Fat
H
H
C
O
OH
HO
C
(CH2)14 CH3
O
H
C
OH
HO
C
(CH2)14 CH3
O
H
C
OH
HO
C
(CH2)14 CH3
H
Glycerol
+
3 fatty acid molecules
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Fig. 4.2b
H
H
C
O
O
C
(CH2)14 CH3
O
H
C
O
C
H2O
+
(CH2)14 CH3
H2O
H2O
O
H
C
O
C
(CH2)14 CH3
H
Fat molecule (triglyceride)
+
3 water
molecules
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Fig. 4.3a
Another example of Anabolism:
Two amino acids joined to make a dipeptide
H
H
N
H
C
O
C
N
O
R
Amino acid
H
H
H
H
+
C
O
C
R
Amino acid
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H
Dipeptide
Fig.
4.3b
Peptide
bond
H
N
H
H
O
C
C
R
R
N
H
C
O
C
+
OH
H O
2
H
Dipeptide molecule
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+
Water
Catabolism
• a decomposition reaction
• the breaking down of larger
molecules to form smaller ones
• releases energy
• often requires H2O
Fig. 4.2
Anabolism - dehydration synthesis - requires energy
H
H
C
O
OH
HO
C
H
(CH2)14 CH3
H
C
O
O
O
H
C
OH
HO
C
C
OH
HO
C
(CH2)14 CH3
H
C
O
C
+
(CH2)14 CH3
(CH2)14 CH3
H
C
O
C
H2O
H2O
H2O
O
H
Glycerol
(CH2)14 CH3
O
O
H
C
(CH2)14 CH3
H
+
3 fatty acid molecules
Fat molecule (triglyceride)
Catabolism - hydrolysis - produces energy
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+
3 water
molecules
Enzymes
• Molecules that speed up
chemical reactions
• Are not used up in the reaction
so they can be recycled
• Usually are proteins
• Names often end in -ase
Action of Enzymes
Fig. 4.4
Substrate molecules
Product molecule
Active site
(a)
Enzyme
molecule
(b)
Enzyme-substrate
complex
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(c)
Unaltered
enzyme
molecule
Fig. 4.5
Substrate
1
Enzyme A
Enzyme Specificity
Substrate
2
Enzyme B
Substrate
3
Enzyme C
Substrate
4
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Enzyme D
Product
Negative feedback mechanism
Fig. 4.6
Inhibition
Rate-limiting
Enzyme A
Substrate
Substrate
2
1
Enzyme B
Substrate
3
Enzyme C
Substrate
4
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Enzyme D
Product
Fig. 4.7
ATP - Adenosine triphosphate
Adenosine
Adenine
Ribose
Phosphates
P
P
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P
ADP to ATP
Fig. 4.8a
Energy transferred
from cellular
respiration used
to reattach
phosphate
P
P
P
P
ATP
P
ADP
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P
Fig. 4.8b
Potential energy is stored in the bonds
between the outer 2 P groups of ATP
Hi energy bonds
P
P
P
ATP
ADP
P
P
P
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Energy is
transferred
and utilized by
metabolic
reactions when
phosphate bond
is broken
Cellular Respiration or
Cellular Metabolism
• The breakdown in the body of
high-energy molecules to
produce energy
• Catabolism of glucose C6H12O6
produces ATP
• Three steps:
– Glycolysis
– Citric Acid Cycle
– Electron transport chain
Glycolysis
Fig. 4.9a
• 1 molecule of glucose (6 carbon)
• results in 2 molecules of pyruvic acid (3 carbon)
• happens in the cytosol
• anaerobic
Glucose
Glycolysis
High-energy electrons (e–)
The 6-carbon sugar glucose is broken down in the cytosol
into two 3-carbon pyruvic acid molecules with a net gain
of 2 ATP and the release of high-energy electrons.
2
Glycolysis
Cytosol
1
Pyruvic acid
Pyruvic acid
2 ATP used and 4 ATP generated = Net 2 ATP
2 electron pairs released to NAD+
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ATP
NAD+ and FAD Deliver High Energy Hydrogen
To the Electron Transport System
NAD+ + 2H
NADH + H+
When NAD+ accepts 2 hydrogen atoms,
the two electrons and a hydrogen nucleus
bind to NAD+ to form NADH.
The remaining H ion (a hydrogen nucleus or
H+ ) is released
FAD + 2H
FADH2
Events After Glycolysis
If O2 Adequate
Pyruvic acid enters
the mitochondrion and
is modified to enter
the citric acid cycle
If O2 not Adequate
Pyruvic acid is converted
into lactic acid until there
is adequate oxygen
for the aerobic steps of
cellular respiration
Fig. 4.9b
Preparation for Citric Acid Cycle
• If O2 is adequate, pyruvic acid enters mitochondrion
• releases a carbon as CO2
• combines with coenzyme A to form acetyl coenzyme A
Pyruvic acid
2
Citric Acid Cycle
The 3-carbon pyruvic acids generated by glycolysis enter
the mitochondria. Each loses a carbon (generating CO2)
and is combined with a coenzyme to form a 2-carbon
acetyl coenzyme A (acetyl CoA). More high-energy
electrons are released.
Pyruvic acid
High-energy electrons (e–)
CO2
Acetyl Co A
One electron pair passed to NAD+
for each molecule of pyruvic acid converted
to Acetyl CoA
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Fig. 4.9c
Citric Acid Cycle or Krebs Cycle
• Acetyl coenzyme A combines with oxaloacetic acid
to form citric acid
• CO2 formed as carbons are removed
• cycle regenerates oxaloacetic acid
• happens aerobically
Acetyl Co A
Each acetyl Co A combines with a 4-carbon oxaloacetic
acid to form the 6-carbon citric acid, for which the cycle
is named. For each citric acid, a series of reactions
removes 2 carbons (generating 2 CO2’s), synthesizes
1 ATP, and releases more high-energy electrons.
The figure shows 2 ATP, resulting directly from 2
turns of the cycle per glucose molecule that enters
glycolysis.
Mitochondrion
3
Citric acid
Oxaloacetic acid
Citric acid
cycle
High-energy electrons (e–)
2 CO2
2
ATP
For each turn of the citric acid cycle:
3 electron pairs passed to NAD+
1 electron pair passed to FAD
1 ATP generated
Fig 4.9
Glucose
2 pr
Glycolysis
The 6-carbon sugar glucose is broken down in the cytosol
into two 3-carbon pyruvic acid molecules with a net gain
of 2 ATP and release of high-energy electrons.
Fig. 4.9
Pyruvic acid
Citric Acid Cycle
2
2
Glycolysis
ATP
Cytosol
1
High-energy electrons (e–)
Pyruvic acid
2 pr
The 3-carbon pyruvic acids generated by glycolysis enter
the mitochondria. Each loses a carbon (generating CO2
and is combined with a coenzyme to form a 2-carbon
acetyl coenzyme A (acetyl CoA). More high-energy
electrons are released.
High-energy electrons (e–)
CO2
Acetyl CoA
3 Each acetyl CoA combines with a 4-carbon oxaloacetic
8 pr total
Citric acid
cycle
3 pr to Nad+/turn
1 pr to Fad+/turn
High-energy electrons (e–)
2 CO2
1 ATP/turn
2
Electron Transport Chain
4
The high-energy electrons still contain most of the
chemical energy of the original glucose molecule.
Special carrier molecules bring the high-energy electrons
to a series of enzymes that convert much of the remaining
energy to more ATP molecules. The other products are
heat and water. The function of oxygen as the final electron
acceptor in this last step is why the overall process is called
aerobic respiration.
Citric acid
Oxaloacetic acid
Mitochondrion
acid to form the 6-carbon citric acid, for which the cycle
is named. For each citric acid, a series of reactions
removes 2 carbons (generating 2 CO2’s), synthesizes
1 ATP, and releases more high-energy electrons.
The figure shows 2 ATP, resulting directly from 2
turns of the cycle per glucose molecule that enters
glycolysis.
ATP
Electron
transport
chain
32–34
2e– and 2H+
1
2 O2
H2 O
ATP
Fig. 4.11
Pyruvic acid from glycolysis
Cytosol
Carbon atom
P
NAD+
Phosphate
MitochondrionCoA Coenzyme A
CO2
NADH + H+
Acetic acid
CoA
Acetyl CoA
Citric
Acid
Cycle
(replenish molecule)
Oxaloacetic acid
Citric acid
(finish molecule)
(start molecule)
CoA
NADH + H+
NAD+
Malic acid
Isocitric acid
NAD+
Citric acid cycle
CO2
NADH + H+
Fumaric acid
a -Ketoglutaric acid
CO2
CoA
NAD+
FADH2
FAD
Succinyl-CoA
Succinic acid
CoA
ADP + P
ATP
NADH + H+
Electron Transport Chain
Fig. 4.12
• Each NADH carried e- pair creates 3 ATP
• Each FADH2 carried e- pair creates 2 ATP
• Oxygen serves as final e- acceptor and produces H20
ADP + P
ATP synthase
ATP
Energy
NADH + H+
Energy
2H+
NAD+
+
2e–
Energy
FADH2
2H+ + 2e–
FAD
Electron transport chain
2e2H+
O2
10 e- pairs carried by NADH = 30 ATP*
2 e- pairs carried by FAD = 4 ATP
Glycolysis
= 2 ATP
Citric Acid Cycle
= 2 ATP
H2O
Net ATP from
1 molecule
Glucose = 38 ATP*
Cellular Respiration Overview
From: Principles of A&P Tortora & Grabowsky
Fig. 4.13
Glucose
High energy
electrons (e–) and
hydrogen ions (H+)
2
Pyruvic acid
ATP
Pyruvic acid
Cytosol
Mitochondrion
High energy
electrons (e–) and
hydrogen ions (h+)
CO2
Acetyl CoA
Oxaloacetic
acid
Citric acid
High energy
electrons (e–) and
hydrogen ions (H+)
2 CO2
2
ATP
Electron transport chain
32-34
1/2 O2
ATP
2e– + 2H+
H 2O
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Fig. 4.15
Food
Food
1
Pg. 134
Fig. 4.15
Proteins
(egg white)
Carbohydrates
(toast, hashbrowns)
Amino acids
Fats
(butter)
Simple sugars
(glucose)
Glycerol
Breakdown of large
macromolecules
to simple molecules
1
Fatty acids
2
Glycolysis
ATP
2
Pyruvic acid
Acetyl coenzyme A
Citric
acid
cycle
3
CO2
ATP
High energy
electrons carried
by NADH and FADH2
Electron
transport
chain
ATP
2e– and 2H+
–NH2
CO2
½ O2
H2 O
Waste products
© Royalty Free/CORBIS.
2
Breakdown of simple
molecules to acetyl
coenzyme A
accompanied by
production of limited
ATP and high energy
electrons
3
Complete oxidation
of acetyl coenzymeA
to H2O and CO2
Produces high energy
electrons(carried by
NADH and FADH2),
which yield much
ATP via the electron
transport chain