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Lecture 7

Enzymes:

Introduction

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Catalyst

• substance that increase rates of achemical reaction

• does not effect equilibrium• remain unchanged in overall

process

• reactants bind to catalyst,products are released

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Catalysts increase product formation by(1) lowering the energy barrier (activation

energy) for the product to form(2) increases the favorable orientation ofcolliding reactant molecules for productformation to be successful (stabilize transition

state intermediate)

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Catalytic Poer

• Enzymes can accelerate reactionsas much as !"!# over uncatalyzed

rates$• %rease is a good e&ample:

– Catalyzed rate: '&!"()sec

– %ncatalyzed rate: '&!" *!")sec

– +atio is !&!"!( $

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pecificity• Enzymes selectively recognize

proper substrates over othermolecules

• Enzymes produce products in very

high yields * often much greaterthan -./

• pecificity is controlled by

structure * the unique fit ofsubstrate ith enzyme controls theselectivity for substrate and the

product yield

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Classes of enzymes!0 1&idoreductases 2 catalyze o&idation*reduction reactions

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90 ransferases 2 catalyze transfer of functional groups from onemolecule to another0

'0 ydrolases 2 catalyze hydrolytic cleavage

(0 Lyases 2 catalyze removal of a group from or addition of agroup to a double bond, or other cleavages involving electron

rearrangement0.0 Isomerases 2 catalyze intramolecular rearrangement0

#0 Ligases 2 catalyze reactions in hich to molecules are ;oined0

Enzymes named for the substrates and type of reaction

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Co*enzymes

• 4on*protein molecules that help enzymesfunction

• 5ssociate ith active site of enzyme• Enzyme < Co*enzyme 2 holoenzyme• Enzyme alone 2 apoenzyme• 1rganic co*enzymes = thiamin, riboflavin,

niacin, biotin• Inorganic co*enzymes = >g

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Kinetics

• study of reaction rate

• determines number of steps involved

• determines mechanism of reaction

• identifies rate!limiting" step