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Energy and MetabolismChapter 8
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Outline Flow of Energy in Living Things Laws of Thermodynamics Free Energy Activation Energy Enzymes
• Forms• Activity
ATP Biochemical Pathways
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Flow of Energy in Living Things
Energy - the capacity to do work• kinetic - energy of motion• potential - stored energy
Thermodynamics - changes in heat• calorie - heat required to raise the
temperature of one gram of water one degree Celsius• kilocalorie = 1000 calories
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Flow of Energy in Living Things
Oxidation - Reduction• Oxidation occurs when an atom or molecule
loses an electron.• Reduction occurs when an atom or molecule
gains an electron.• Redox reactions occur because every electron that
is lost by an atom through oxidation is gained by some other atom through reduction.
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Fig. 8.3 (TEArt)
Product
H
H
H
H
NAD+
NAD
NAD
H
Energy-rich molecule
1. Enzymes that harvesthydrogen atoms have abinding site for NAD+
located near anotherbinding site. NAD+ andan energy-richmolecule bind tothe enzyme.
3. NADH thendiffuses away andis available toother molecules.
2. In an oxidation-reduction reaction,a hydrogen atomis transferred toNAD+, formingNADH.
Enzyme
NAD+NAD+
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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Laws of Thermodynamics
First Law of Thermodynamics• Energy cannot be created or destroyed, but
only change form.• During each conversion, some of the energy
dissipates into the environment as heat.• Heat is defined as the measure of the random
motion of molecules.
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Laws of Thermodynamics
Second Law of Thermodynamics• The disorder (entropy) in the universe is
continuously increasing.• Energy transformations proceed spontaneously to
convert matter from a more ordered, less stable form, to a less ordered, more stable form.
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Free Energy
Free energy refers to the amount of energy actually available to break and subsequently form other chemical bonds.• Gibbs’ free energy (G)
• change in free energy• endergonic - any reaction that requires an input of energy• exergonic - any reaction that releases free energy
Important Note: All reactions require an Activation Energy
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Activation Energy
Activation energy refers to the extra energy required to destabilize existing chemical bonds and initiate a chemical reaction.• catalyst - substance that lowers the activation
energy• cannot violate laws of thermodynamics.
• direction of a chemical reaction is determined solely by the difference in free energy between the reactants and the products
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Activation Energy and Catalysis
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Enzymes Are Biological Catalysts
Enzymes are proteins that carry out most catalysis in living organisms.• Unique three-dimensional shape enables an
enzyme to stabilize a temporary association between substrates.• Because the enzyme itself is not changed or
consumed in the reaction, only a small amount is needed, and can then be reused.
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Enzymes
Most enzymes are globular proteins with one or more active sites.• Substrates bind to the enzyme at these active
sites, forming an enzyme-substrate complex.• Often end in suffix ase but not always.
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Fig. 8.9 (TEArt)
The substrate,sucrose, consistsof glucose andfructose bondedtogether.
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The substratebinds to theenzyme, formingan enzyme-substratecomplex.
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The binding ofthe substrateand enzymeplaces stress onthe glucose-fructose bond,and the bondbreaks.
3
Products arereleased, andthe enzyme isfree to bindothersubstrates.
4Bond
Enzyme
Active site
H2O
Glucose Fructose
Copyright © The McGraw-Hil l Companies, Inc. Permission required for reproduction or display.
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Enzyme Forms
A multienzyme complex is composed of several enzymes, catalyzing the different steps of a sequence of reactions, that are associated with one another.• subunits work in concert, providing significant
advantages in catalytic efficiency RNA catalysts “ribozymes”
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CARBONIC ANHYDRASE
Read about Carbonic Anhydrase
Page 149
How much does C.A increase the rate of reaction?
What is the “knife” in this enzyme?
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Pyruvate Dehydrogenase What does it do?
60 protein subunits, a very COMPLEX COMPLEX
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Factors Affecting Enzyme Activity
Temperature• Rate of an enzyme-catalyzed reaction
increases with temperature, but only up to an optimum temperature.
pH• Ionic interactions also hold enzymes together.
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Factors Affecting Enzyme Activity
Inhibitors and activators• inhibitor - substance that binds to an enzyme
and decreases its activity• competitive inhibitors - compete with the substrate
for the same active site• noncompetitive inhibitors - bind to the enzyme in a
location other than the active site• allosteric sites - specific binding sites acting as
on/off switches
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Factors Affecting Enzyme Activity
• activator - substances that bind to allosteric sites and keep the enzymes in their active configurations• increase enzyme activity
• cofactors - chemical components that facilitate enzyme activity (minerals)
• Coenzyme (vitamins)
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ATP
Adenosine triphosphate (ATP) is the chief energy currency of the cell.• Each molecule is a nucleotide composed of
ribose, adenine, and a triphosphate group.• energy stored in the triphosphate group
• cell uses ATP to drive endergonic reactions
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Biochemical Pathways
Biochemical pathways are the organizational units of metabolism.• Metabolism is the total of all chemical reactions
carried out by an organism.• anabolism- reactions that expend energy to make bonds• catabolism - reactions that harvest energy when bonds are
broken
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Regulation of Biochemical Pathways
Biochemical pathways must be coordinated and regulated to operate efficiently.• advantageous for cell to temporarily shut down
biochemical pathways when their products are not needed• feedback inhibition - When the cell produces increasing
quantities of a particular product, it automatically inhibits its ability to produce more.
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Feedback Inhibition
The Concept of REGULATION is a KEY CONCEPT in Biology
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Feedback Mechanisms
Negative Feedback- Brings the amount of final product back to a baseline
Positive Feedback- Brings the amount of product away from a baseline.
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Summary
Flow of Energy in Living Things Laws of Thermodynamics Free Energy Activation Energy Enzymes
• Forms• Activity
ATP Biochemical Pathways
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See Chapter 8 Animation “Feedback Inhibition of Biochemical Pathways
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