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
Fig. 4.1a
CH2OH
H H
OH
O
H OH
Monosaccharide(glucose)
+
HHO
H
OH
H H
OH
O
H OH
Monosaccharide(glucose)
HHO
H
OH
CH2OH
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Formation of a disaccharide:a molecule of H20 is removed
H20
Fig. 4.1b
H H
OH
O
H OH
Disaccharide(maltose)
H2O
Water+
HHO
H H H
OH
O
H OH
HO
H
OH
CH2OH CH 2OH
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An example of Anabolism:A Disaccharide is formed by dehydration synthesis
+
Fig. 4.2a
H C
H
Glycerol 3 fatty acid molecules+
OH HO
H C OH HO
H C
C
C
COH HO
OH
O
O
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(CH2)14 CH3
(CH2)14 CH3
(CH2)14 CH3
Dehydration Synthesis of a Fat
Fig. 4.2b
C
C
C
O
O
O
H C
H
Fat molecule (triglyceride) 3 water molecules
+
H C
H C O
O
O
H
H2O
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H2O
H2O
(CH2)14 CH3
(CH2)14 CH3
(CH2)14 CH3
+
Fig. 4.3a
Amino acid + Amino acid
N
H
H
C C
H
R H
O
N
H
H
C C
H
R H
O
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O
Another example of Anabolism:Two amino acids joined to make a dipeptide
Fig. 4.3b
N
H
H
C
R
Dipeptide molecule +
Peptidebond
H
N
H
OH
H
O
N H2O
Water
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O
C CC
R
+
Dipeptide
Catabolism
• a decomposition reaction
• the breaking down of larger
molecules to form smaller ones
• releases energy
• often requires H2O
Fig. 4.2
H C
H
Glycerol 3 fatty acid molecules+
OH HO
H C OH HO
H C
C
C
COH HO
OH
O
O
C
C
C
O
O
O
H C
H
Fat molecule (triglyceride) 3 watermolecules
+
H C
H C O
O
O
H
H2O
(CH2)14 CH3
H2O
H2O
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(CH2)14 CH3
(CH2)14 CH3
(CH2)14 CH3
(CH2)14 CH3
(CH2)14 CH3
Anabolism - dehydration synthesis - requires energy
Catabolism - hydrolysis - produces energy
+
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
Fig. 4.4
Unalteredenzymemolecule
Enzyme-substratecomplex
Active site
(a) (b) (c)
Enzymemolecule
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Product moleculeSubstrate molecules
Action of Enzymes
Fig. 4.5
Substrate1
Enzyme A Substrate2
Enzyme B Substrate3
Enzyme C Substrate4
Enzyme DProduct
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Enzyme Specificity
Fig. 4.6
Inhibition
Substrate1
Substrate2
Enzyme B Substrate3
Enzyme C Substrate4
Enzyme DProduct
Rate-limitingEnzyme A
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Negative feedback mechanism
Fig. 4.7
Ribose
Adenosine
P P P
Adenine
Phosphates
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ATP - Adenosine triphosphate
Fig. 4.8a
Energy transferredfrom cellularrespiration usedto reattachphosphate
P P
P P P
P
ADP
ATP
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ADP to ATP
Fig. 4.8b
ADP
ATP
Energy is transferred and utilized bymetabolicreactions whenphosphate bondis brokenP P
P P P
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P
Potential energy is stored in the bonds between the outer 2 P groups of ATP
Hi energy bonds
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
Fig. 4.9a
1 Glycolysis
Cyt
oso
l
ATP2
Glucose
High-energy electrons (e–)
Pyruvic acidPyruvic acid
The 6-carbon sugar glucose is broken down in the cytosolinto two 3-carbon pyruvic acid molecules with a net gainof 2 ATP and the release of high-energy electrons.
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Glycolysis
Glycolysis
2 ATP used and 4 ATP generated = Net 2 ATP
2 electron pairs released to NAD+
• 1 molecule of glucose (6 carbon)• results in 2 molecules of pyruvic acid (3 carbon)• happens in the cytosol• anaerobic
NAD+ + 2H NADH + H+
NAD+ and FAD Deliver High Energy Hydrogen To the Electron Transport System
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 If O2 not Adequate
Pyruvic acid is convertedinto lactic acid until thereis adequate oxygenfor the aerobic steps of cellular respiration
Pyruvic acid enters the mitochondrion andis modified to enterthe citric acid cycle
Fig. 4.9b
2High-energy electrons (e–)
CO2
Pyruvic acidPyruvic acid
Acetyl Co A
The 3-carbon pyruvic acids generated by glycolysis enterthe mitochondria. Each loses a carbon (generating CO2)and is combined with a coenzyme to form a 2-carbonacetyl coenzyme A (acetyl CoA). More high-energy electrons are released.
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Citric Acid Cycle
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
One electron pair passed to NAD+
for each molecule of pyruvic acid convertedto Acetyl CoA
Fig. 4.9c
3
Mit
och
on
dri
on
High-energy electrons (e–)
ATP2
Acetyl Co A
Citric acid
Citric acidcycle
Oxaloacetic acidEach acetyl Co A combines with a 4-carbon oxaloaceticacid to form the 6-carbon citric acid, for which the cycleis named. For each citric acid, a series of reactionsremoves 2 carbons (generating 2 CO2’s), synthesizes1 ATP, and releases more high-energy electrons.The figure shows 2 ATP, resulting directly from 2turns of the cycle per glucose molecule that entersglycolysis.
2 CO2
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
For each turn of the citric acid cycle:3 electron pairs passed to NAD+1 electron pair passed to FAD1 ATP generated
Fig. 4.91
3
4
2
Glycolysis
Cyt
oso
lM
ito
cho
nd
rio
n
ATP2
Glucose
High-energy electrons (e–)
2e– and 2H+
2
H2OO2
Electrontransport
chain ATP32–34
Pyruvic acidPyruvic acid
2 CO2
Acetyl CoA
Citric acid
Citric acidcycle
Oxaloacetic acid
High-energy electrons (e–)
High-energy electrons (e–)
ATP
Glycolysis
The 6-carbon sugar glucose is broken down in the cytosolinto two 3-carbon pyruvic acid molecules with a net gainof 2 ATP and release of high-energy electrons.
Citric Acid Cycle
The 3-carbon pyruvic acids generated by glycolysis enterthe mitochondria. Each loses a carbon (generating CO2
and is combined with a coenzyme to form a 2-carbonacetyl coenzyme A (acetyl CoA). More high-energy electrons are released.
Each acetyl CoA combines with a 4-carbon oxaloaceticacid to form the 6-carbon citric acid, for which the cycleis named. For each citric acid, a series of reactions removes 2 carbons (generating 2 CO2’s), synthesizes1 ATP, and releases more high-energy electrons.The figure shows 2 ATP, resulting directly from 2turns of the cycle per glucose molecule that entersglycolysis.
Electron Transport Chain
The high-energy electrons still contain most of thechemical energy of the original glucose molecule.Special carrier molecules bring the high-energy electronsto a series of enzymes that convert much of the remaining energy to more ATP molecules. The other products areheat and water. The function of oxygen as the final electronacceptor in this last step is why the overall process is calledaerobic respiration.
12
CO2
2 pr
2 pr
3 pr to Nad+/turn1 pr to Fad+/turn
1 ATP/turn
8 pr total
Fig 4.9
Fig. 4.11
Citric acid cycle
ADP +ATP
Pyruvic acid from glycolysis
Citric acid
(start molecule)
Acetyl CoA
(replenish molecule)
Acetic acid
Oxaloacetic acid
(finish molecule)
Isocitric acid
CO2
CO2
Succinyl-CoASuccinic acidFAD
FADH2
Fumaric acid
Malic acid
Cytosol
MitochondrionNADH + H+
NAD+
NADH + H+
NAD+
NADH + H+
NAD+
CoA
CoA
CoA
CoA
P
NADH + H+
NAD+
P
CoA Coenzyme A
Carbon atom
Phosphate
-Ketoglutaric acida
CO2
Citric AcidCycle
Fig. 4.12
ATPADP +ATP synthase
Electron transport chain
Energy
P
2H+ + 2e–
2e-
2H+
NADH + H+
NAD+FADH2
FAD
O2
H2O
Energy
Energy
2H+ + 2e–
Electron Transport Chain• 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
10 e- pairs carried by NADH = 30 ATP*2 e- pairs carried by FAD = 4 ATPGlycolysis = 2 ATPCitric Acid Cycle = 2 ATP
Net ATP from 1 moleculeGlucose = 38 ATP*
From: Principles of A&P Tortora & Grabowsky
Cellular Respiration Overview
Fig. 4.13
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ATP2
ATP2
Glucose
Pyruvic acid Pyruvic acid
Acetyl CoA
CO2
2 CO2
Citric acidOxaloacetic
acid
H2O
2e– + 2H+
High energyelectrons (e–) andhydrogen ions (H+)
High energy
electrons (e–) and
hydrogen ions (H+)
Electron transport chain
ATP32-34
Cytosol
Mitochondrion
High energyelectrons (e–) andhydrogen ions (h+)
1/2 O2
Fig. 4.15
High energyelectrons carried
by NADH and FADH2
H2O
2e– and 2H+
Waste products
–NH2
CO2
CO2
Citricacidcycle
Electrontransport
chain
Amino acids
Acetyl coenzyme A
Simple sugars(glucose)
Glycerol Fatty acids
Proteins(egg white)
Carbohydrates(toast, hashbrowns)
Food
Fats(butter)
Pyruvic acid
ATP
ATP
Glycolysis
1
2
3
ATP
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½ O2
Fig. 4.15
High energyelectrons carried
by NADH and FADH2
Complete oxidationof acetyl coenzymeA to H2O and CO2
Produces high energy electrons(carried by NADH and FADH2), which yield muchATP via the electrontransport chain
Breakdown of simplemolecules to acetylcoenzyme Aaccompanied byproduction of limitedATP and high energyelectrons
H2O
2e– and 2H+
Waste products
–NH2
CO2
CO2
Citricacidcycle
Electrontransport
chain
Amino acids
Acetyl coenzyme A
Simple sugars(glucose)
Glycerol Fatty acids
Proteins(egg white)
Carbohydrates(toast, hashbrowns)
Food
Fats(butter)
Pyruvic acid
ATP
ATP
Breakdown of largemacromoleculesto simple molecules
Glycolysis
1
2
3
ATP
© Royalty Free/CORBIS.
½ O2
2
1
3
Pg. 134