Chemical Reactions Chemical Reactions and Enzymesand Enzymes

2-42-4

Chemical ReactionsChemical Reactions Process that changes one set of Process that changes one set of

chemicals into another set of chemicals into another set of chemicalschemicals

Occur at different ratesOccur at different rates

Reactants - elements or compounds Reactants - elements or compounds that enter reactionthat enter reaction

Products – elements or compounds at Products – elements or compounds at end of reactionend of reaction

Chemical reactions always involve Chemical reactions always involve the breaking of bonds and the the breaking of bonds and the forming of new bondsforming of new bonds

Examples: H + Cl Examples: H + Cl HCl HCl

Na + Cl Na + Cl NaCl NaCl

Energy in ReactionsEnergy in Reactions

Energy is released or absorbed Energy is released or absorbed whenever chemical bonds form or are whenever chemical bonds form or are brokenbroken

Since bonds are broken and reformed in Since bonds are broken and reformed in chemical reactions, c.r. involve changes chemical reactions, c.r. involve changes in energyin energy

Energy changes are an important factor Energy changes are an important factor in determining if a chem. rxn will happenin determining if a chem. rxn will happen

C.R. that release energy occur C.R. that release energy occur spontaneously (exergonic)spontaneously (exergonic)

C.R. that absorbs energy will not C.R. that absorbs energy will not occur without a source of energy occur without a source of energy (endergonic)(endergonic)

Ex: 2HEx: 2H22 + O + O22 2H 2H22O give off energyO give off energy

2H2H22O O 2H 2H22 + O + O22 needs needs energyenergy

Significance of Energy Significance of Energy ChangesChanges

Living things need to carry out rxns Living things need to carry out rxns that require energy that require energy – get energy from sun (plants) or food get energy from sun (plants) or food

(animals)(animals)

Energy is released in daily processes Energy is released in daily processes like growing, breathing, thinkinglike growing, breathing, thinking

Energy is released by metabolizing or Energy is released by metabolizing or breaking down foodbreaking down food

Activation EnergyActivation Energy

Not all rxns that release energy Not all rxns that release energy happen spontaneouslyhappen spontaneously

Activation energy - energy needed Activation energy - energy needed to get a reaction startedto get a reaction started

A.E. is a factor in whether the overall A.E. is a factor in whether the overall chemical reaction releases or chemical reaction releases or absorbs energyabsorbs energy

EnzymesEnzymes

Some chemical reactions that make Some chemical reactions that make life possible have A.E. that are too life possible have A.E. that are too high, or happen too slowlyhigh, or happen too slowly

In order to make rxn happen at a In order to make rxn happen at a logical rate, catalysts are usedlogical rate, catalysts are used

Catalysts – substances that speed up Catalysts – substances that speed up the rate of rxn by lowering A.E.the rate of rxn by lowering A.E.

Cells make catalysts - enzymesCells make catalysts - enzymes

Enzymes are proteins that act as Enzymes are proteins that act as biological catalystsbiological catalysts

Enzymes are very specific and Enzymes are very specific and usually catalyze only 1 reactionusually catalyze only 1 reaction

Enzyme names are derived from rxn Enzyme names are derived from rxn it catalyzesit catalyzes– Ex: carbonic anhydrase – removes HEx: carbonic anhydrase – removes H22O O

from carbonic acidfrom carbonic acid

Enzyme ActionEnzyme Action

Enzymes provide a site where Enzymes provide a site where reactants can be brought together to reactants can be brought together to reactreact– Site reduces A.E.Site reduces A.E.– Reactants are called substrateReactants are called substrate

Substrates bind to a region of Substrates bind to a region of enzyme known as active siteenzyme known as active site

Active site is shaped complimentary Active site is shaped complimentary to substrateto substrate– Called “lock and key”Called “lock and key”

Once bonded (active site & Once bonded (active site & substrate), an enzyme substrate substrate), an enzyme substrate complex is formedcomplex is formed– They stay together until rxn is doneThey stay together until rxn is done– Products are releasedProducts are released– Enzyme can be used again Enzyme can be used again

Regulating EnzymesRegulating Enzymes

Enzymes can be affected by any Enzymes can be affected by any variable that can influence rxnvariable that can influence rxn

Enzymes used to digest food work at Enzymes used to digest food work at certain pH valuescertain pH values

Enzymes are also affected by Enzymes are also affected by temperaturetemperature

Cells can regulate activities of Cells can regulate activities of enzymesenzymes– Contain proteins that can turn key Contain proteins that can turn key

enzymes “on & off”enzymes “on & off”

Enzymes play essential roles in:Enzymes play essential roles in:– Regulating chemical pathwaysRegulating chemical pathways– Making materials that cells needMaking materials that cells need– Releasing energyReleasing energy– Transferring informationTransferring information