Chemical Reactions and Enzymes

Section 2.4

Chemical Reaction Review• Reactions involve changes in the chemical

bonds of substances.• Mass and energy are conserved.• Reaction rates vary. (rusting vs. combustion)• Reactants and products

Energy in Reactions

• Some chemical reactions release energy (exothermic) in the form of heat, light, and sound. – Exothermic reactions can to be spontaneous.

• Example: cell respiration

• Some reactions absorb energy (endothermic).– Endothermic reactions will not occur without a source

of energy.• Example: photosynthesis

Exothermic reactionEndothermic reaction

Enzymes• Enzymes are proteins that act as biological catalysts which

speed up chemical reactions that take place in cells.• Without enzymes, some biological processes would happen

too slowly to maintain homeostasis.• Enzymes are very specific, generally catalyzing only one

chemical reaction, from which the name of the enzyme is derived.

Enzyme Substrates• Substrates are the reactants of enzyme

catalyzed reactions.• Substrates bind to a site on the enzyme called

the active site.• The fit is so precise that the active site is

compared to a lock and key.• http://www.youtube.com/watch?v=0XGiIE9b9QU

Enzyme Regulation• Temperature, pH, and regulatory molecules can

affect the activity of enzymes.• The enzyme can become denatured.• http://www.youtube.com/watch?v=E-_r3omrnxw• What is an inhibitor? How can inhibitors change

enzyme activity?