ENZYMES Consider Burning: C6H12O6 + O2  CO2 + H2O C6H12O6 + 6O2  6CO2 + 6H2O

What does it take to burn cellulose? Molecules must hit hard enough together and at the correct angle to cause bonds to rearrange. This requires “activation energy.” Usually supplied by adding heat to increase the energy of the hit and the number of times they will probably hit at the correct angle.

Chemical Reactions Reactant Energy Product Energy

What does it take to burn starch? Same thing, but you can’t swallow a flame thrower!

Enzymes Almost all enzymes are proteins Catalyze chemical reactions (make reactions go faster than they normally would) by lowering the activation energy. When dealing with enzymes, the reactants are called substrate molecules

Lock-and-Key Model The substrate binds to the active site of the enzyme. The active site has a complementary shape.

Enzyme Characteristics. Enzymes: Are proteins (globular proteins). Usually end in –ase (compare to sugars that end in –ose). Are specific: each catalyzes only one type of chemical reaction. Are named for the reaction or reactants they work on. E.g., Hydrogen peroxidase breaks down hydrogen peroxide  Are not used up in a chemical reaction. They are recycled. Can often work in reverse. Often have vitamins attached that help determine their shape (and thus activity).

Enzymes are not used up in a chemical reaction and often work in reverse.

The Lock-and-Key Model has been replaced by the “Induced Fit” model The Lock-and-Key Model has been replaced by the “Induced Fit” model. The Active Site works “hugging” the substrate.

Effect of other atoms or molecules on enzymes

What conditions affect how enzymes work? Classic Enzyme function curve Temperature pH Salt Concentration Number of enzymes Concentration of substrate (Enzyme Kinetics “Lab”)

Each enzyme has its own specific set of optimal environmental conditions. Optimal temperature for enzyme of thermophilic (heat-tolerant) bacteria Optimal temperature for typical human enzyme Rate of reaction Temperature (ºC) (a) Optimal temperature for two enzymes Optimal pH for pepsin (stomach enzyme) Optimal pH for trypsin (intestinal enzyme) Rate of reaction (b) Optimal pH for two enzymes