cell metabolism
DESCRIPTION
Cell Metabolism. Energy. Energy is the capacity to do work. A handful of peanuts contains enough energy to boil a quart of water. Energy Forms. Forms of energy: Potential energy Kinetic energy. Conversion of potential energy to kinetic energy. High potential energy. - PowerPoint PPT PresentationTRANSCRIPT
MetabolismMetabolism
Cell MetabolismCell Metabolism
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EnergyEnergy
Energy is the capacity to do work.Energy is the capacity to do work.
A handful of A handful of peanuts contains peanuts contains enough energy to enough energy to boil a quart of boil a quart of waterwater
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Energy FormsEnergy Forms
Forms of energy:Forms of energy:• Potential energyPotential energy
• Kinetic energyKinetic energy
High potential energy
Conversion ofpotential energyto kinetic energy
Low potential energyConversion of kinetic energy to potential energy
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Cellular WorkCellular Work
Cells use energy for:Cells use energy for:• Mechanical workMechanical work• Transport workTransport work• Chemical workChemical work
Cellular Work Cellular Work = Metabolism= Metabolism It takes about 10 It takes about 10
million ATP molecules million ATP molecules per second to power per second to power an active muscle cell.an active muscle cell.
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First Law of ThermodynamicsFirst Law of Thermodynamics
The total amount of The total amount of energy in the universe energy in the universe remains constant.remains constant.
Energy can be Energy can be transformed from one transformed from one form to another, but it form to another, but it cannot be created or cannot be created or destroyed.destroyed.
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Second Law of ThermodynamicsSecond Law of Thermodynamics
Energy transformations increase entropy Energy transformations increase entropy (degree of disorder) in a closed system.(degree of disorder) in a closed system.– No energy conversion is 100 percent efficient.No energy conversion is 100 percent efficient.
Systems tend to Systems tend to go from states of go from states of higher free energy higher free energy to states of lower to states of lower free energy.free energy.
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Exergonic ReactionsExergonic Reactions
AA BB
EnergyReleased
CC DD
++
++
High EnergyHigh EnergyReactantsReactants
Low EnergyLow EnergyProductsProductsEnergy is released.
Products have less energy than starting substance.
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Exergonic ExampleExergonic Example
EnergyReleased
++
++High EnergyHigh EnergyReactantsReactants
Low EnergyLow EnergyProductsProducts
OHO
OCH2OH
O O
O OC
OHH
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Exergonic Energy DiagramExergonic Energy Diagram
EnergyEnergycontentcontent
ofofmoleculesmolecules
highhigh
lowlow
An exergonic reaction: Burning GlucoseAn exergonic reaction: Burning Glucose
Progress of reactionProgress of reaction
Activation energy neededActivation energy neededto start reactionto start reaction
Activation energy neededActivation energy neededto start reactionto start reaction
Glucose + OGlucose + O22Glucose + OGlucose + O22
Energy Energy releasedreleased by byburning glucoseburning glucose
Energy Energy releasedreleased by byburning glucoseburning glucose
C OC O22 + H + H22OOC OC O22 + H + H22OO
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Endergonic ReactionsEndergonic Reactions
AA BB++
CC DD++
Low EnergyLow EnergyReactantsReactants
High EnergyHigh EnergyProductsProducts
energyenergy
Energy input is required
Products store more energy
than starting substances.
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Endergonic Energy DiagramEndergonic Energy Diagram
EnergyEnergycontentcontent
ofofmoleculesmolecules
highhigh
lowlow
(b)(b) An endergonic reaction: An endergonic reaction: PhotosynthesisPhotosynthesis
Progress of reactionProgress of reaction
GlucoseGlucoseGlucoseGlucose
Net energyNet energyincreaseincrease by bysynthesizingsynthesizing
glucoseglucose
COCO22 + H + H22OOCOCO22 + H + H22OO
ActivationActivationenergy fromenergy fromlight light storedstored
by by photosynthesisphotosynthesis
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Endergonic ExampleEndergonic Example
++
Low EnergyLow EnergyReactantsReactants ++
High EnergyHigh EnergyProductsProducts
OHO
OCH2OH
O O
O OC
OHH
EnergySupplied
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Energy FlowEnergy Flow
Energy flows into ecosystems as sunlight. Energy flows into ecosystems as sunlight. (The sun is life’s primary energy source.)(The sun is life’s primary energy source.)Producers (autotrophs) trap energy from Producers (autotrophs) trap energy from the sun and convert it into chemical bond the sun and convert it into chemical bond energy.energy.All organisms use the energy stored in the All organisms use the energy stored in the bonds of organic compounds to do work.bonds of organic compounds to do work. LIVING SYSTEMS ARE LIVING SYSTEMS ARE NOTNOT CLOSED CLOSED SYSTEMS!SYSTEMS!
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Energy RelationshipsEnergy Relationships
ATP
BIOSYNTHETIC PATHWAYS
(ANABOLIC)
ENERGY INPUT
DEGRADATIVE PATHWAYS
(CATABOLIC)
energy-poor products(such as carbon dioxide, water)
large energy-rich molecules(fats, complex carbohydrates,
proteins, nucleic acids)
simple organic compounds(simple sugars, amino acids,
fatty acids, nucleotides)
ADP + Pi
Chemical reactions either store or release energy.Chemical reactions either store or release energy.
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The Role of ATPThe Role of ATP
Cells “earn” ATP in exergonic reactions.Cells “earn” ATP in exergonic reactions.
Cells “spend” ATP in endergonic reactions.Cells “spend” ATP in endergonic reactions.
P P P
ribose
adenine
ATP - adenosine triphosphate
16ADP & ATPADP & ATP
OH
PPO
O
O PP OH
OH
O
~~RiboseRibose
HH22CCHH22CC
HHHH
OOOO
HHHH
OHOHOHOHOHOHOHOH
HHHHHHHH
NNNNHCHCHCHC
NNNN CCCC
CCCC
CCCC
CHCHCHCH
NNNN
NNNN
NHNH22NHNH22
AdenineAdenine
Adenosine
Adenosine
PP OH
OH
O
OH
PPO
O
O PP O
OH
O
~~RiboseRibose
HH22CCHH22CC
HHHH
OOOO
HHHH
OHOHOHOHOHOHOHOH
HHHHHHHH
NNNNHCHCHCHC
NNNN CCCC
CCCC
CCCC
CHCHCHCH
NNNN
NNNN
NHNH22NHNH22
AdenineAdenine
Adenosine
Adenosine
~~
DiPhosphateDiPhosphate
TriPhosphateTriPhosphate
ADPADP
ATPATP
High-energyHigh-energyPhosphatePhosphate
BondBond
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Coupled Reactions: SynthesisCoupled Reactions: Synthesis
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Coupled Reaction: PhosphorylationCoupled Reaction: Phosphorylation
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Coupled Reactions: Muscle ActionCoupled Reactions: Muscle Action
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Active TransportActive Transport
ATP gives up phosphate ATP gives up phosphate to activate protein.to activate protein.
Binding of ATP changes Binding of ATP changes protein shape and protein shape and affinity for solute.affinity for solute.
P
P
P
P
High solute concentration
Low solute concentration
ATP ADP
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Electron CarriersElectron Carriers
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Enzyme ActionEnzyme Action
a. Enzymes speed up metabolic reactions by lowering activation energy.
b. Enzymes are substrate specific.
c. Enzyme activity is regulated by inhibitors.
d. A cell’s physical and chemical environment effects enzyme activity.
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Hydrolysis of SucroseHydrolysis of Sucrose
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Enzymes are CatalystEnzymes are Catalysta. Enzymes speed up metabolic
reactions by lowering activation energy
• A catalyst is a chemical agent that changes the rate of a reaction without being consumed by the reaction.
• An enzyme is a catalytic protein.• Enzymes regulate the movement of
molecules through metabolic pathways.
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““Lowering” Activation EnergyLowering” Activation Energy
A + B
C + D
A B298oK, no catalyst
T, no catalyst298oK, inorganic catalyst298oK, enzyme
Fig. 2
EnergyEnergycontentcontent
ofofmoleculesmolecules
highhigh
lowlow
Progress of reactionProgress of reaction
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Metabolic PathwaysMetabolic Pathways
AA BB CC DDDD EEEE
FFFF GGGG
Enzyme 1Enzyme 1 Enzyme 2Enzyme 2 Enzyme 3Enzyme 3 Enzyme 4Enzyme 4
Enzyme 5Enzyme 5 Enzyme 6Enzyme 6
InitialInitialReactantsReactants
IntermediatesIntermediates FinalFinalProductsProducts
Pathway 1Pathway 1Pathway 1Pathway 1
Pathway 2Pathway 2Pathway 2Pathway 2
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Enzymes SpecificityEnzymes Specificity
b. Enzymes are substrate specific• A substrate is a reactant which binds to
an enzyme.• When a substrate or substrates binds to
an enzyme, the enzyme catalyzes the conversion of the substrate to the product.
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Enzyme Active SitesEnzyme Active Sites
• The active site of an enzyme is a pocket or groove on the surface of the protein.• The specificity of an enzyme is due to the fit between the active site and the substrate.• As the substrate binds, the enzyme changes shape leading to a tighter induced fit.
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substrate
enzyme
E + S
Induced Fit ModelInduced Fit Model
Fig. 3
initial binding due to e.g., charge interactions
ES*
enzyme-substrate(ES) complex
inductionof fit
ES
enzyme
products
E + Psubstrate contact
with active siteenzyme unchanged
by reaction TRANSITION STATE good orientation but unstable
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Enzyme-Substrate InteractionsEnzyme-Substrate InteractionsSubstrateSubstrateSubstrateSubstrateSubstrateSubstrateSubstrateSubstrate
EnzymeEnzymeEnzymeEnzyme
ActiveActiveSiteSite
ActiveActiveSiteSite
11 Substrates Substrates enter active enter active sitesite
11 Substrates Substrates enter active enter active sitesite
22 Shape change Shape change promotes reactionpromotes reaction
22 Shape change Shape change promotes reactionpromotes reaction
33 Product released;Product released;enzyme ready againenzyme ready again
33 Product released;Product released;enzyme ready againenzyme ready again
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c. Enzyme activity is regulated by inhibitors.
• Some molecules inhibit enzymes from catalyzing reactions.
• If the inhibitor binds to the same site as the substrate, then it blocks substrate binding via competitive inhibition.
• If the inhibitor binds somewhere other than the active site, it blocks substrate binding via noncompetitive inhibition.
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Negative Feedback ModelsNegative Feedback Models
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End Product InhibitionEnd Product Inhibition
Prevents excess accumulation of final product.Results in alternative pathway and product.
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E 5E 5E 5E 5DDDD
E 4E 4E 4E 4CCCC
E 3E 3E 3E 3BBBB
Feedback InhibitionFeedback Inhibition
E 2E 2E 2E 2AAAA
Feedback InhibitionFeedback InhibitionIsoleucine inhibits enzyme 1Isoleucine inhibits enzyme 1
E 1E 1E 1E 1
CHCH33CHCH33
CCCC
CCCC
COOHCOOHCOOHCOOH
OHOHOHOH
NHNH33NHNH33HHHH
HHHHCHCH22
CHCH22
CCCC
CCCC
COOHCOOHCOOHCOOH
CHCH33CHCH33
NHNH33NHNH33HHHH
HHHH
CHCH33CHCH33
ThreonineThreonine(substrate)(substrate)ThreonineThreonine(substrate)(substrate) IsoleucineIsoleucine
(end product)(end product)IsoleucineIsoleucine
(end product)(end product)
35Allosteric Regulation vs. CompetitionAllosteric Regulation vs. Competition
SubstrateSubstrateSubstrateSubstrate
EnzymeEnzymeEnzymeEnzyme
Active Active SiteSite
Active Active SiteSite
Allosteric Allosteric SiteSite
Allosteric Allosteric SiteSite
(a)(a)
Allosteric Allosteric Regulatory Regulatory
MoleculeMolecule
Allosteric Allosteric Regulatory Regulatory
MoleculeMolecule
Shape of activeShape of activesite changedsite changed(b)(b)
(c)(c)
Competitive inhibitorCompetitive inhibitoroccupies active siteoccupies active site
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Effects on Enzyme ActionEffects on Enzyme Action
d. A cell’s physical and chemical environment effects enzyme activity
• The three-dimensional structure of enzymes depend on environmental conditions.
• Changes in shape influence the reaction rate.
• Some conditions lead to the most active conformation and optimal rate of reaction.
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Effect of pHEffect of pH
• pH influences shape and reaction rate.
• Each enzyme has an optimal pH (usually between pH 6 – 8).
• However, digestive enzymes in the stomach are designed to work best at pH 2 while those in the intestine are optimal at pH 9.
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Effect of TemperatureEffect of Temperature
• As temperature increases, collisions between substrates and active sites occur more frequently.
• At some point, thermal agitation begins to destabilize the protein’s active conformation and the protein denatures.
• Each enzyme has an optimal temperature.
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Effect of Cofactors & CoenzymesEffect of Cofactors & Coenzymes
• Many enzymes require nonprotein cofactors for catalytic activity and include zinc, iron, and copper.
• Organic cofactors, coenzymes, include vitamins or molecules derived from vitamins.
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Effect of Substrate ConcentrationEffect of Substrate Concentration
• The rate of product The rate of product formation increases formation increases as the [substrate] as the [substrate] increases.increases.
• Rate levels when Rate levels when enzyme becomes enzyme becomes saturated.saturated.
• Additional substrate Additional substrate does not not increase does not not increase reaction rate.reaction rate.
MetabolismMetabolism
The endThe end