Chapter 8Chapter 8Enzymes, Energy, and Enzymes, Energy, and

MetabolismMetabolism

EnergyEnergy

Energy is the Energy is the capacity to do workcapacity to do work, or the , or the capacity for changecapacity for change..

Energy transformations are linked to Energy transformations are linked to chemical transformations (reactions)chemical transformations (reactions) in in cells.cells.

Types of EnergyTypes of Energy

Potential energyPotential energy: is stored energy: is stored energy

- chemical bonds- chemical bonds

- concentration gradient- concentration gradient

- charge imbalance, etc.- charge imbalance, etc.

Kinetic energyKinetic energy: is the energy of movement: is the energy of movement

BiochemistryBiochemistryMetabolismMetabolism: Sum total of all chemical reactions : Sum total of all chemical reactions in an organism.in an organism.

Anabolic reactionsAnabolic reactions: Complex molecules are : Complex molecules are made from simple molecules; energy input is made from simple molecules; energy input is required.required.

Catabolic reactionsCatabolic reactions: Complex molecules are : Complex molecules are broken down to simpler ones and energy is broken down to simpler ones and energy is released.released.

Laws of ThermodynamicsLaws of Thermodynamics

Thermo - “energy”Thermo - “energy”

Dynamics - “change”Dynamics - “change”

Apply to all matter and all energy Apply to all matter and all energy transformations in the universe.transformations in the universe.

First Law of ThermodynamicsFirst Law of Thermodynamics

Energy is Energy is neither created nor destroyedneither created nor destroyed..

When energy is converted from one form When energy is converted from one form to another, the total energy before and to another, the total energy before and after the conversion is the same.after the conversion is the same.

Second Law of Second Law of ThermodynamicsThermodynamics

When energy is converted from one form to When energy is converted from one form to another, another, some of that energy becomes some of that energy becomes unavailable to do workunavailable to do work..

No energy transformation is 100% efficient.No energy transformation is 100% efficient.

How is Energy Related…How is Energy Related…In any system:In any system:

Total energy = usable energy + unusable energyTotal energy = usable energy + unusable energy

enthalpy (H) = free energy (G) + entropy (S)enthalpy (H) = free energy (G) + entropy (S)

H = G + TS H = G + TS (T = absolute temperature)(T = absolute temperature)

G = H – TSG = H – TS

EntropyEntropy is a measure of the disorder in a system. is a measure of the disorder in a system.

Energy to do WorkEnergy to do Work

Change in Change in free energy (free energy (ΔΔG)G) in a reaction is in a reaction is the difference in free energy of the the difference in free energy of the products and the reactants.products and the reactants.

ΔΔG = G = ΔΔH – TH – TΔΔSS•If If ΔΔGG is negative, free energy is released is negative, free energy is released

•If If ΔΔG G is positive, free energy is consumedis positive, free energy is consumed

•At chemical equilibrium, At chemical equilibrium, ΔΔG = 0G = 0

BiochemistryBiochemistry

Exergonic reactionsExergonic reactions release free energy release free energy (–(–ΔΔG): Catabolism; complexity G): Catabolism; complexity decreases (generates disorder).decreases (generates disorder).

Endergonic reactionsEndergonic reactions consume free consume free energy (+energy (+ΔΔG): anabolism; complexity G): anabolism; complexity (order) increases.(order) increases.

BiochemistryBiochemistry

ATPATPATP (adenosine triphosphate) captures ATP (adenosine triphosphate) captures and transfers free energy.and transfers free energy.

ATP releases a large amount of energy ATP releases a large amount of energy when hydrolyzed.when hydrolyzed.

ATP canATP can phosphorylate, or donate phosphorylate, or donate phosphate groups to other molecules.phosphate groups to other molecules.

ATPATP

Hydrolysis of ATP Hydrolysis of ATP yields free energy.yields free energy.

ΔΔG = –7.3 to –14 G = –7.3 to –14 kcal/mol (exergonic)kcal/mol (exergonic)

ATP↔ADPATP↔ADP

CatalystsCatalysts

Speed up the Speed up the raterate of a reaction. of a reaction.

The catalyst is not altered by the The catalyst is not altered by the reactions.reactions.

Most biological catalysts are Most biological catalysts are enzymesenzymes (proteins) that act as a framework in which (proteins) that act as a framework in which reactions can take place.reactions can take place.

EnzymesEnzymesHighly specificHighly specific

Reactants are called Reactants are called substratessubstrates

Substrate molecules bind to the Substrate molecules bind to the active siteactive site of of the enzymethe enzyme

The three-dimensional shape of the enzyme The three-dimensional shape of the enzyme determines the specificitydetermines the specificity

EnzymesEnzymes

The The enzyme-substrate complexenzyme-substrate complex (ES) is held together by (ES) is held together by hydrogen bonds, electrical attraction, or covalent bonds.hydrogen bonds, electrical attraction, or covalent bonds.

E + S E + S → → ES → E + PES → E + P

The enzyme may change when bound to the substrate, but The enzyme may change when bound to the substrate, but returns to its original form. returns to its original form.

Enzymes Lower the Energy Barrier Enzymes Lower the Energy Barrier for Reactionsfor Reactions

Activation EnergyActivation Energy: : The amount of energy The amount of energy needed to initiate a needed to initiate a reaction reaction

All reactions require All reactions require activation energy.activation energy.

Exergonic vs. Exergonic vs. Endergonic ReactionsEndergonic Reactions

Enzyme PartnersEnzyme Partners

Prosthetic groupsProsthetic groups: : (Permanent) Non-(Permanent) Non-amino acid groups amino acid groups bound to enzymesbound to enzymes

CofactorsCofactors: : (Reversible) Inorganic (Reversible) Inorganic ionsions

CoenzymesCoenzymes: : (Reversible) Small (Reversible) Small carbon-containing carbon-containing moleculesmolecules

The rate of a catalyzed reaction The rate of a catalyzed reaction depends on substrate concentrationdepends on substrate concentration

Concentration of an Concentration of an enzyme is usually enzyme is usually much lower than much lower than concentration of a concentration of a substrate.substrate.

At At saturationsaturation, all , all enzyme is bound to enzyme is bound to substratesubstrate

Enzyme Regulation Enzyme Regulation

InhibitorsInhibitors: :

Molecules that bind to Molecules that bind to the enzyme and slow the enzyme and slow reaction rates.reaction rates.

Naturally occurring Naturally occurring inhibitors regulate inhibitors regulate metabolism.metabolism.

2 Groups of Inhibitors:2 Groups of Inhibitors:- Reversible Reversible - IrreversibleIrreversible

Irreversible inhibitionIrreversible inhibition: : Inhibitor covalently Inhibitor covalently bonds to side chains in bonds to side chains in the active site and the active site and permanently permanently inactivates the enzyme.inactivates the enzyme.

Naturally Occurring InhibitorsNaturally Occurring Inhibitors

Reversible inhibitionReversible inhibition: Inhibitor bonds : Inhibitor bonds noncovalently to the active site and prevents noncovalently to the active site and prevents substrate from binding.substrate from binding.

2 Types:2 Types:– Competitive InhibitorsCompetitive Inhibitors– Noncompetitive InhibitorsNoncompetitive Inhibitors

Competitive InhibitorsCompetitive Inhibitors

Compete with the Compete with the natural substrate for natural substrate for binding sites.binding sites.

When concentration of When concentration of competitive inhibitor competitive inhibitor is reduced, it detaches is reduced, it detaches from the active site.from the active site.

Noncompetitive InhibitorsNoncompetitive Inhibitors

Bind to the enzyme at Bind to the enzyme at a different site (not the a different site (not the active site).active site).

The enzyme changes The enzyme changes shape and alters the shape and alters the active site.active site.

Metabolic PathwaysMetabolic PathwaysMetabolismMetabolism is the thousands of chemical is the thousands of chemical reactions occurring in cells simultaneouslyreactions occurring in cells simultaneously

These reactions are organized in These reactions are organized in metabolic metabolic pathwayspathways. .

Each reaction is catalyzed by a specific Each reaction is catalyzed by a specific enzyme.enzyme.

The pathways are interconnected.The pathways are interconnected.

Regulation of enzymes and thus reaction Regulation of enzymes and thus reaction rates helps maintain internal homeostasis.rates helps maintain internal homeostasis.

Metabolic Pathways Metabolic Pathways

The first reaction is the The first reaction is the commitment stepcommitment step—other —other reactions then happen in reactions then happen in sequence.sequence.

Feedback inhibition Feedback inhibition (end-(end-product inhibition): The product inhibition): The final product acts as a final product acts as a noncompetitive inhibitornoncompetitive inhibitor of the first enzyme, which of the first enzyme, which shuts down the pathway.shuts down the pathway.

Coniferyl Alcohol

Cinnamate 4 -hydrolase

ChorismateShikimate

Acid Pathway

Glycolysis & Pentose

Phosphate Pathway

Chorismate Mutase

PrephenatePrephenate

AminotransferaseArogenate

Arogenate dehydratase

Phenylalanine

PAL

Chalcone Synthase

cinnomyl alcohol dehydrogenaseBSMT

(SAMT)

BEBT

Anthocyanins, Flavanoids, Isoflavons

Chalcones

Para Coumarate

Para Cinnamic Acid

Trans Cinnamic Acid

2-Phenylethanol

Phenylethylamine

Tryptophan

Ferulic Acid

Phenylacetaldehyde

DOXP/ME Pathway

Coniferyl aldehyde

Caffeic Acid

CCOMT IEMT

COMT

o-Coumarate

IsoeugenolEugenol

IEMT

Benzoic Acid

Methyleugenol Methylisoeugenol

CCOMT

BSMT (BAMT)

Benzoic acid 2- hydrolase

Methylbenzoate

Methylsalicylate

Salicylic Acid

Benzylbenzoate Benzylalcohol

Benzaldehyde

Benzylacetate

Mevalonic Acid

Pathway

DMAPP

GPP

IPP IPP

DMAPP

Sesquiterpenes

(Caryophyllene)

Monoterpenes

(Linalool)

Lignins

???

???

???

BEAT

Tyrosine

TAL

?IST

A generalized schematic of biochemical pathways involved in VOC synthesis

FPP

?IST