Chemical Reactions and Enzymes 2-4

Chemical Reactions Process that changes one set of chemicals into another set of chemicals Process that changes one set of chemicals into another set of chemicals Occur at different rates Occur at different rates Reactants - elements or compounds that enter reaction Reactants - elements or compounds that enter reaction Products – elements or compounds at end of reaction Products – elements or compounds at end of reaction

Chemical reactions always involve the breaking of bonds and the forming of new bonds Chemical reactions always involve the breaking of bonds and the forming of new bonds Examples: H + Cl  HCl Examples: H + Cl  HCl Na + Cl  NaCl Na + Cl  NaCl

Energy in Reactions Energy is released or absorbed whenever chemical bonds form or are broken Energy is released or absorbed whenever chemical bonds form or are broken Since bonds are broken and reformed in chemical reactions, c.r. involve changes in energy Since bonds are broken and reformed in chemical reactions, c.r. involve changes in energy Energy changes are an important factor in determining if a chem. rxn will happen Energy changes are an important factor in determining if a chem. rxn will happen

C.R. that release energy occur spontaneously (exergonic) C.R. that release energy occur spontaneously (exergonic) C.R. that absorbs energy will not occur without a source of energy (endergonic) C.R. that absorbs energy will not occur without a source of energy (endergonic) Ex: 2H 2 + O 2  2H 2 O give off energy Ex: 2H 2 + O 2  2H 2 O give off energy 2H 2 O  2H 2 + O 2 needs energy

Significance of Energy Changes Living things need to carry out rxns that require energy Living things need to carry out rxns that require energy –get energy from sun (plants) or food (animals) Energy is released in daily processes like growing, breathing, thinking Energy is released in daily processes like growing, breathing, thinking Energy is released by metabolizing or breaking down food Energy is released by metabolizing or breaking down food

Activation Energy Not all rxns that release energy happen spontaneously Not all rxns that release energy happen spontaneously Activation energy - energy needed to get a reaction started Activation energy - energy needed to get a reaction started A.E. is a factor in whether the overall chemical reaction releases or absorbs energy A.E. is a factor in whether the overall chemical reaction releases or absorbs energy

Enzymes Some chemical reactions that make life possible have A.E. that are too high, or happen too slowly Some chemical reactions that make life possible have A.E. that are too high, or happen too slowly In order to make rxn happen at a logical rate, catalysts are used In order to make rxn happen at a logical rate, catalysts are used Catalysts – substances that speed up the rate of rxn by lowering A.E. Catalysts – substances that speed up the rate of rxn by lowering A.E.

Cells make catalysts - enzymes Cells make catalysts - enzymes Enzymes are proteins that act as biological catalysts Enzymes are proteins that act as biological catalysts Enzymes are very specific and usually catalyze only 1 reaction Enzymes are very specific and usually catalyze only 1 reaction Enzyme names are derived from rxn it catalyzes Enzyme names are derived from rxn it catalyzes –Ex: carbonic anhydrase – removes H 2 O from carbonic acid

Enzyme Action Enzymes provide a site where reactants can be brought together to react Enzymes provide a site where reactants can be brought together to react –Site reduces A.E. –Reactants are called substrate Substrates bind to a region of enzyme known as active site Substrates bind to a region of enzyme known as active site

Active site is shaped complimentary to substrate Active site is shaped complimentary to substrate –Called “lock and key” Once bonded (active site & substrate), an enzyme substrate complex is formed Once bonded (active site & substrate), an enzyme substrate complex is formed –They stay together until rxn is done –Products are released –Enzyme can be used again

Regulating Enzymes Enzymes can be affected by any variable that can influence rxn Enzymes can be affected by any variable that can influence rxn Enzymes used to digest food work at certain pH values Enzymes used to digest food work at certain pH values Enzymes are also affected by temperature Enzymes are also affected by temperature

Cells can regulate activities of enzymes Cells can regulate activities of enzymes –Contain proteins that can turn key enzymes “on & off” Enzymes play essential roles in: Enzymes play essential roles in: –Regulating chemical pathways –Making materials that cells need –Releasing energy –Transferring information