biology 102 lecture 3: enzymes - linn–benton...

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Biology 102Biology 102

Lecture 3: EnzymesLecture 3: Enzymes

•• Chemical reactions are a rearrangement of the Chemical reactions are a rearrangement of the atoms and bonds in chemical substancesatoms and bonds in chemical substances

•• Atoms are not created or destroyed Atoms are not created or destroyed –– just just rearrangedrearranged

•• Law of Conservation of MassLaw of Conservation of Mass

•• Energy is always involvedEnergy is always involved

Chemical ReactionsChemical Reactions

•• All chemical reactions in the body = All chemical reactions in the body = metabolismmetabolism

•• Chemical reactions are responsible for many Chemical reactions are responsible for many processes in the bodyprocesses in the body

•• GrowthGrowth

•• RepairRepair

•• DigestionDigestion


•• Many types of chemical reactionsMany types of chemical reactions

•• Most either…Most either…

•• Build things up Build things up

•• Break things downBreak things down


•• Larger reactants break down to form simpler Larger reactants break down to form simpler productsproducts

•• Energy is Energy is released released in these reactionsin these reactions

•• Important in digestionImportant in digestion

•• Can take place inside or outside of cellsCan take place inside or outside of cells

AB AB --> A + B> A + B

Catabolic ReactionsCatabolic Reactions

•• Smaller reactants combine to form more Smaller reactants combine to form more complex productscomplex products

•• Require energyRequire energy

•• Important in growth and tissue buildingImportant in growth and tissue building

A + B A + B --> AB> AB

Anabolic ReactionsAnabolic Reactions

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•• Catabolic and anabolic reactions are required to Catabolic and anabolic reactions are required to build up build up biomoleculesbiomolecules and tissuesand tissues


•• Primary energy source for metabolism is Primary energy source for metabolism is

chemical energy stored in bondschemical energy stored in bonds

•• In animals = food moleculesIn animals = food molecules

•• In plants = photosynthesisIn plants = photosynthesis

•• More bonds means moreMore bonds means more

energy storedenergy stored

•• Why fat is high inWhy fat is high in

caloriescalories

Chemical EnergyChemical Energy

•• As these molecules are broken down, energy is As these molecules are broken down, energy is

releasedreleased

•• Catabolic reactionsCatabolic reactions


Potential energy

•• This energy is then used to drive the building up This energy is then used to drive the building up

of other moleculesof other molecules

•• Anabolic reactionsAnabolic reactions


Potential energy

•• Metabolic reactions are an “uphill battle”Metabolic reactions are an “uphill battle”

•• Energy must be put in to drive reactionEnergy must be put in to drive reaction

•• True even if energy is released in reactionTrue even if energy is released in reaction

•• Minimum energy required = Minimum energy required = activation energy activation energy (E(Eaa))


Potential energy

Potential energy

•• EEaa can be overcome by increasing temperaturecan be overcome by increasing temperature

•• But we would cook!But we would cook!

•• At body temperature, metabolic reactions At body temperature, metabolic reactions

proceed too slowly to sustain lifeproceed too slowly to sustain life

•• And yet we live!And yet we live!

•• Nature has found a way around thisNature has found a way around this


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•• Catalysts speed up chemical reactions without being Catalysts speed up chemical reactions without being used up or changed in the reactionused up or changed in the reaction

•• Reduce activation energyReduce activation energy

•• Can be used over and overCan be used over and over

•• EnzymesEnzymes are a class of proteins that act as catalystsare a class of proteins that act as catalysts


Potential energy

EnzymesEnzymes

•• Enzymes have an Enzymes have an active siteactive site that only binds a that only binds a

specific reactants, called the specific reactants, called the substratesubstrate

•• HIGHLY specific interactionHIGHLY specific interaction

•• Substrate is converted to products and releasedSubstrate is converted to products and released

EnzymesEnzymes

•• Active site may bind only one substrate and help Active site may bind only one substrate and help

break it downbreak it down

•• Example: Example: sucrasesucrase

•• Question: catabolicQuestion: catabolic

or anabolic reaction?or anabolic reaction?

EnzymesEnzymes

•• Active site may bind more than one substrate at Active site may bind more than one substrate at

a timea time

•• Question: catabolic or anabolic reaction?Question: catabolic or anabolic reaction?

EnzymesEnzymes

•• Enzyme activity an important drug targetEnzyme activity an important drug target

•• Inhibition or activationInhibition or activation

•• Examples: Examples: COXCOX--2 inhibitors (e.g. Celebrex), MAOIs, 2 inhibitors (e.g. Celebrex), MAOIs, certain antibiotics, some diuretics, some certain antibiotics, some diuretics, some

chemotherapy agentschemotherapy agents

Key Enzyme PointsKey Enzyme Points

•• ProteinsProteins

•• Biological catalystsBiological catalysts

•• Critical to nearly every biological processCritical to nearly every biological process

•• Extremely specificExtremely specific

•• Lower activation energy for reactionsLower activation energy for reactions

•• Can be reusedCan be reused

•• Important drug targetsImportant drug targets

biology 102 lecture 3: enzymes - linn–benton...

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