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Chapter 6: Energy and Metabolism
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Biological Work Requires Energy
• Remember to study the terms
• Energy Concepts Video
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Fig. 8-2
Climbing up converts the kineticenergy of muscle movementto potential energy.
A diver has less potentialenergy in the waterthan on the platform.
Diving convertspotential energy tokinetic energy.
A diver has more potentialenergy on the platformthan in the water.
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2 Laws of Thermodynamics
• 1.) Energy cannot be created or destroyed, but it can be transferred or changed from 1 form to another
• Photosynthesis:– Sun’s energy chemical energy in bonds of carbs– Later
• Chemical energy cellular work OR mechanical energy
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• 2.) energy is converted from 1 from to another; some usable energy is converted to heat (disperses into surroundings)
• SO – total amount of energy available to do work is decreasing over time
• Total amount of energy overall remains constant
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Fig. 8-3
(a) First law of thermodynamics (b) Second law of thermodynamics
Chemicalenergy
Heat CO2
H2O+
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Entropy
• Measure of disorder or randomness• Less-usable energy is more disorganized• Organized = low entropy• Disorganized = high entropy
– Ex: heat• Entropy – continuously increasing in universe
in all natural processes– As more heat is released, our universe becomes
more disorganized
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Enthalpy
• Total potential energy of the system
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Free Energy
• Amount of energy available to do work under the conditions of a biochemical reaction
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H = G + TS
• H = enthalpy• G = free energy• T = absolute temperature in K• S = entropy• Can’t effectively measure total free energy but
can measure CHANGES, so ΔG = ΔH - TΔS
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Reactions
• Exergonic – release energy HL• Endergonic – gain energy from surroundings• Activation energy – needed to start a reaction• Coupled reaction – endergonic + exergonic
– exergonic reaction provides energy required to drive endergonic reaction
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Fig. 8-6
Reactants
Energy
Free
ene
rgy
Products
Amount ofenergyreleased(∆G < 0)
Progress of the reaction(a) Exergonic reaction: energy released
Products
ReactantsEnergy
Free
ene
rgy Amount of
energyrequired(∆G > 0)
(b) Endergonic reaction: energy requiredProgress of the reaction
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Enzymes – How Enzymes Work Video
• Enzyme – protein catalyst– Lower activation energy
• Catalyst– Speed up reaction
• Substrate – substance that enzyme acts on• Enzyme-Substrate complex –
– Enzymes orders structure of substrate– Gets reaction going– When breaks product + original enzyme
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Enzymes
• Active site – on enzyme, where substrate binds
• Induced Fit – substrate binds, changes shape of enzyme– Enzyme and substrate not exactly complementary
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Fig. 8-17
Substrates
Enzyme
Products arereleased.
Products
Substrates areconverted toproducts.
Active site can lower EAand speed up a reaction.
Substrates held in active site by weakinteractions, such as hydrogen bonds andionic bonds.
Substrates enter active site; enzyme changes shape such that its active siteenfolds the substrates (induced fit).
Activesite is
availablefor two new
substratemolecules.
Enzyme-substratecomplex
5
3
21
6
4
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Enzymes
• Some – all protein• Some – 2 parts – work together to function
– 1) protein = apoenzyme– 2) chemical component = cofactor ( C or no C)
– Coenzyme – C, nonpolypeptide• Binds to apoenzyme as cofactor
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Enzymes are most Effective At Certain Conditions
• Temperature– Most – temp increases, reaction rate increases– Low temp = slow– Too high temp. – denatures enzymes
• pH – enzyme active in narrow range• Charge – affect ionic bonds for tertiary and
quaternary structure
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Fig. 8-18
Rat
e of
reac
tion
Optimal temperature forenzyme of thermophilic
(heat-tolerant) bacteria
Optimal temperature fortypical human enzyme
(a) Optimal temperature for two enzymes
(b) Optimal pH for two enzymes
Rat
e of
reac
tion
Optimal pH for pepsin(stomach enzyme)
Optimal pHfor trypsin(intestinalenzyme)
Temperature (ºC)
pH543210 6 7 8 9 10
0 20 40 80 60 100
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Concentrations of Enzyme and Substrate
• Lots substrate – enzyme concentration limits• Less substrate than enzyme – substrate
concentration limits
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Enzyme Activity
• Feedback Inhibition– Formation of a product inhibits an earlier reaction
in the sequence of reactions
– A B C D E
– When E is low – sequence proceeds rapidly– E is high – E1 slows and can stop entire sequence
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Fig. 8-UN1
Enzyme 1 Enzyme 2 Enzyme 3DCBA
Reaction 1 Reaction 3Reaction 2Startingmolecule
Product
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• Allosteric Regulation– Substance binds to enzyme’s allosteric site,
changing shape of active site and modifying enzyme’s activity
– Allosteric site = receptor site on enzyme, not active site
– Allosteric regulators – affect enzyme activity by binding to allosteric sites
• Keep inactive• activate
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Fig. 8-20 Allosteric enyzmewith four subunits
Active site(one of four)
Regulatorysite (oneof four)
Active formActivator
Stabilized active form
Oscillation
Non-functionalactivesite
InhibitorInactive form Stabilized inactiveform
(a) Allosteric activators and inhibitors
Substrate
Inactive form Stabilized activeform
(b) Cooperativity: another type of allosteric activation
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Enzyme Inhibition – can be inhibited or destroyed by certain chemicals
• Reversible Inhibition – inhibitor forms weak chemical bonds w/ enzyme– Competitive – inhibitor competes w/ normal
substrate for active site• No permanent damage
– Noncompetitive – inhibitor binds w/ enzyme but not at active site
• e enzymes by altering shape
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Fig. 8-19
(a) Normal binding (c) Noncompetitive inhibition(b) Competitive inhibition
Noncompetitive inhibitor
Active siteCompetitive inhibitor
Substrate
Enzyme
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• Irreversible Inhibition – inhibitor permanently inactivates or destroys an enzyme when it combines w/ enzyme at active site or elsewhere– Ex: poison
• Mercury, lead, nerve gas, cyanide