enzymes - proteins that control most reactions in cells

• biocatalysts - speeds up metabolic reactions to biologically useful rates
• lowers activation energy needed for reaction to start
• substrate - reacting molecules that binds to the enzyme to make enzyme-substrate complex
  • active site - where substrate attaches to the enzyme
• provides energy of activation to form the transition state (making substrate more reactive)
• completes reaction when product formed, enzyme goes back to original shape
• structure/shape determines enzyme’s function
• denaturation - structural change to enzyme, can destroy its effectiveness
• optimal conditions - the environmental conditions under which the enzyme works the best
• phosphate-carrying molecules like ATP turn enzymes on/off through phosphorylation

effect of temperature on enzyme activity

• heat usually increases rate of most chemical reactions (puts energy into the system)
• extreme temperatures may denature enzymes

catechol oxidase - plant enzyme converting catechol to benzoquinone

• benzoquinone responsible for brown color in bruised fruit
• catechol >> catechol oxidase >> benzoquinone
• no reaction if either catechol oxidase or catechol missing
• low temperatures >> slower reaction
• moderately high temperatures (about 40° C) >> fast reaction
• extremely high temperatures (about 80° C) >> denatured enzyme, no reaction

effect of pH on enzyme activity

• H+ and OH- groups from acids/bases react w/ side groups of enzyme molecules
• lower pH >> more H+ ions
• higher pH >> more OH- ions
• can change enzyme shape enough to change active site

catalase - enzyme in plants/animals, speeds up hydrogen peroxide breakdown

• 2 H2O2>> catalase >> 2 H2O + O2
• no reaction if either catalase or hydrogen peroxide missing
• works best in neutral pH
• adding acid/base/buffer can change the pH

effect of inhibitors on enzyme activity  

• competitive inhibition - inhibitors that compete for the same active site as a substrate
  • makes enzyme unavailable for substrate
• can also bond to allosteric site and shut off enzyme