Enzymes

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

Remember that proteins have a very specific structure Primary through quaternary structure must be maintained for the protein to function properly What happens if it is not? – an enzyme’s shape is changed so that it is no longer able to catalyze reactions, we call it… DENATURED

Denaturation Disruption of secondary, tertiary and quaternary 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 the 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

How do enzymes work? Lower Activation Energy to speed up rates of reaction (of chemical reactions) –Reactions require energy to begin…enzymes lower the amount of energy required. Amount of energy Reaction Rate Without an enzyme With an enzyme Activation energy

Naming Often end in “–ase” The name usually relates to the reactants they are associated with or the reaction they help start

A specific enzyme catalyzes each cellular reaction 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 –ACTIVE SITE: region of the enzyme where the substrate fits (lock and key)

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

Lock and Key Model The enzyme remains the same before/after the rxn, while the substrate changes to new products after the rxn + + E + S ES complex E + P S P P S

The cellular environment affects enzyme activity. An enzyme is most effective under certain conditions.

Temperature Temperature affects molecular motion an enzyme’s optimal temperature produces the highest rate. -(Most human enzymes work best at ºC.) WATCH OUT!!! If the temperature gets too high, the enzyme may be denatured!

Factors Affecting Enzyme Action Optimum temperature Reaction Rate Low High Temperature

Ions Salt concentration and pH influence enzyme activity. SALT: Salt ions can interfere with the chemical bonds that maintain protein structure. pH: The same is true of the extra hydrogen ions at very low pH. -The optimal pH for most enzymes is near neutral. Where is the charged area on the following R groups?

Factors Affecting Enzyme Action: 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

Factors Affecting Enzyme Action Maximum activity Reaction Rate substrate concentration

Enzyme Inhibition Inhibitors Cause a loss of catalytic activity –May change the protein structure of an enzyme

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 Inhibitor

Competitive Inhibitor Examples Methanol poisoning occurs because methanol is oxidized to formaldehyde and formic acid which attack the optic nerve causing blindness. Ethanol is given as an antidote for methanol poisoning because ethanol competitively inhibits the oxidation of methanol. Ethanol is oxidized in preference to methanol and consequently, the oxidation of methanol is slowed down so that the toxic by-products do not have a chance to accumulate. Ethylene glycol (found in antifreeze) if ingested, can be poisonous. Ethylene glycol is oxidized by the same enzymes used in the previous examples by ethanol and methanol.

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

Noncompetitive Inhibitor