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Enzymes

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.

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Enzymes

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  1. Enzymes

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

  3. 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.

  4. 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

  5. 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 substrateof the enzyme.

  6. 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.

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

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

  9. 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?

  10. 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

  11. 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

  12. Think about it 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.

  13. Factors Affecting Enzyme Action • Temperatureaffects 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!

  14. Temperature (cont.) Optimum temperature Reaction Rate Low High Temperature

  15. 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

  16. 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

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

  18. 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

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

  20. Competitive Inhibition Image

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

  22. Noncompetitive Inhibition Image

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