Enzymes

Characteristics of Enzymes Proteins Catalysts Speed up chemical reactions without being used up

How do enzymes work? Lower Activation Energy to speed up rates of reaction Reactions require energy to begin…enzymes lower the amount of energy required.

Naming Often end in “–ase” The name usually relates to the reactants they are associated with or the reaction they help start Examples: maltase, sucrase, protease, carboxypeptidase

Catalyzing Process A unique 3-D shape of an enzyme determines which chemical reaction it catalyzes Important Vocab: SUBSTRATE: A specific reactant that an enzyme acts on is called a substrate of the enzyme.

Important Vocab (cont.): ACTIVE SITE: A substrate fits into a region of the enzyme called an active site. An active site is typically a pocket or groove on the surface of the enzyme.

The enzyme and substrate form a complex Active site enzyme Enzyme-substrate complex

Lock and Key Model + + E + S ES complex E + P S P

Structure If an enzyme’s shape is changed so that it is no longer able to catalyze reactions, we call it… DENATURED What kinds of things do you think could denature a protein?

Denaturation Disruption of protein structure by Heat: Break apart H bonds and disrupt hydrophobic attractions Acids/ bases: Break H bonds between polar R groups and ionic bonds Heavy metal ions: React with S-S bonds to form solids Agitation: Stretches chains until bonds break

Applications of Denaturation Hard boiling an egg Wiping skin with alcohol swab for injection Cooking food to destroy E. coli Heat used to cauterize blood vessels Autoclave sterilizes instruments Milk is heated to make yogurt

Think about it Solution Tannic acid is used to form a scab on a burn. An egg becomes hard boiled when placed in hot water. What is similar about these two events? Solution Acid and heat cause a denaturation of protein. They both break bonds in the structure of protein.

Factors Affecting Enzyme Action Temperature affects molecular motion An enzyme’s optimal temperature produces the highest rate Most human enzymes work best at 35-40 ºC. WATCH OUT!!! If the temperature gets too high, the enzyme may be denatured!

Temperature (cont.) Optimum temperature Low High Reaction Rate

Ions: Salt concentration & pH influence enzyme activity. SALT: The salt ions interfere with some of the chemical bonds that maintain protein structure pH: The same is true of the extra hydrogen ions at very low pH Optimal pH for most enzymes near neutral

Substrate Concentration Increasing substrate concentration increases the rate of reaction (enzyme concentration is constant) Why? Maximum activity reached when all of enzyme combines with substrate

Substrate Concentration (cont.) Maximum activity Reaction Rate substrate concentration

Enzyme Inhibition Inhibitors: cause a loss of catalytic activity May change the protein structure of an enzyme May be competitive or noncompetitive Some effects are irreversible

Competitive Inhibition A competitive inhibitor Has a structure similar to substrate Occupies active site “Competes” with substrate for active site Effects can be reversed by increasing substrate concentration

Competitive Inhibition Image

Noncompetitive Inhibition A noncompetitive inhibitor Does not have a structure like substrate Binds to the enzyme (not at active site) & changes the shape of enzyme & active site Substrate cannot fit altered active site No reaction occurs Effect is not reversed by adding substrate

Noncompetitive Inhibition Image