Chemical Reactions and Enzymes Chemistry isn’t just what life is made of; it’s also what life does.

Objectives  What happens to chemical bonds during chemical reactions?  How do energy changes affect whether a chemical reaction will occur?  Why are enzymes important to living things?

Chemical Reactions A chemical reaction is a process that changes one set of chemicals into another set of chemicals

Chemical Reactions The elements or compounds that enter into a chemical reaction are known as reactants. The elements or compounds produced by a chemical reaction are known as products.

What happens to chemical bonds? Chemical reactions always involve the breaking of bonds in reactants and the formation of new bonds in products. CO 2 H2OH2O

What happens to chemical bonds? Chemical reactions always involve the breaking of bonds in reactants and the formation of new bonds in products. CO 2 H2OH2O C 6 H 12 O 6 O2O2

Energy Changes Energy is released or absorbed whenever chemical bonds are formed or broken. Chemical reactions that release energy often occur spontaneously Chemical reactions that absorb energy will not occur without a source of energy

Chemical Reactions- Activation Energy Chemists call the energy that is needed to get a reaction started the activation energy.

Catalyst-Enzymes Some chemical reactions that make life possible are too slow or have activation energies that are too high to make them practical for living things.  These chemical reactions are made possible by catalysts.  Catalysts speed up the rate of a chemical reaction by lowering its activation energy  Although a catalyst helps a chemical reaction to happen, it is unchanged at the end of the reaction.

Catalyst-Enzymes  Enzymes are proteins that act as biological catalysts (FYI: all enzymes are catalysts, but not all catalysts are enzymes).  Enzymes speed up chemical reactions that take place in the cell.  Essentially they lower the amount of work it takes to get a reaction going, so the chemical reaction can take place sooner and quicker. Before Enzyme After Enzyme

Enzyme Action Ok, but how do enzymes lower the amount of energy needed to start a chemical reaction? The enzyme-substrate complex is the answer!

Enzyme-Substrate Complex  Enzymes provide a site where reactants can be brought together to react, reducing the energy needed for reaction.  The reactants of enzyme-catalyzed reactions are known as substrates  Substrates = reactants

Enzyme-Substrate Complex It fits! Active site Substrate Lactose (glucose + galactose) glucosegalactose nom nom!

Enzyme-Substrate Complex  Enzymes will only work for the specific substrate that fits into their active site.  The shape of the enzyme (protein) is essential to the enzymes function. If the protein/enzyme is not folded correctly, the enzyme won’t have the correct active site and won’t be able to work.

Enzymes What happens to an enzyme after the reaction it catalyzes has taken place?  Once the reaction is over, the products of the reaction are released and the enzyme is free to start the process again.  Enzymes are NOT “used up” during a reaction. They can be used over and over and over again for the same substrate!!

Enzymes Enzymes can be affected by the following variables:  pH values  Changes in temperature  Enzyme or substrate concentrations  Co-factors and inhibitors

Enzymes Made of protein Present in all living cells Converts substrates into products Biological catalysts Increase the rate of chemical reactions Remain unchanged by chemical reaction