2What are Enzymes? Enzymes are proteins. Enzymes allow many chemical reactions to occur within the homeostasis constraints of a living system. Enzymes function as organic catalysts.A catalyst is a chemical involved in, but not changed by, a chemical reaction.Many enzymes function by lowering the activation energy of reactions. By bringing the reactants closer together, chemical bonds may be weakened and reactions will proceed faster than without the catalyst. The use of enzymes can lower the activation energy of a reaction (Ea).
3Name of Enzymes End in –ase Identifies a reacting substance sucrase – reacts with sucroselipase - reacts with lipidDescribes function of enzymeoxidase – catalyzes oxidationhydrolase – catalyzes hydrolysisCommon names of digestion enzymes still use –inpepsin, trypsin
4Enzyme Action: Lock and Key Model An enzyme binds a substrate in a region called the active siteOnly certain substrates can fit the active siteAmino acid R groups in the active site help the substrate to bindEnzyme-substrate complex formsSubstrate reacts to form productProduct is released(OR an enzyme may be used to hydrolyse -split- a substrate molecule)
5Enzyme Action: Induced Fit Model Enzyme structure flexible, not rigidEnzyme and active site adjust shape to bind substrateIncreases range of substrate specificityShape changes also improve catalysis during reaction
7Learning Check E2 The active site is (1) the enzyme (2) a section of the enzyme(3) the substrateB. In the induced fit model, the shape of the enzyme when substrate binds(1) Stays the same(2) adapts to the shape of the substrate
8Solution E2 The active site is (2) a section of the enzyme B. In the induced fit model, the shape of the enzyme when substrate binds(2) adapts to the shape of the substrate
9Enzyme Inhibition Inhibitors cause a loss of catalytic activity Change the protein structure of an enzymeMay be competitive or noncompetitiveSome effects are irreversible
10Competitive Inhibition A competitive inhibitorHas a structure similar to substrateOccupies active siteCompetes with substrate for active siteHas effect reversed by increasing substrate concentration
11Noncompetitive Inhibition A noncompetitive inhibitorDoes not have a structure like substrateBinds to the enzyme but not active siteChanges the shape of enzyme and active siteSubstrate cannot fit altered active siteNo reaction occursEffect is not reversed by adding substrate
12Learning Check E4Identify each statement as describing an inhibitor that is(1) Competitive (2) NoncompetitiveA. Increasing substrate reverses inhibitionB. Binds to enzyme, not active siteC. Structure is similar to substrateD. Inhibition is not reversed with substrate
13Solution E4 Identify each statement as describing an inhibitor that is (1) Competitive (2) NoncompetitiveA Increasing substrate reverses inhibitionB Binds to enzyme, not active siteC Structure is similar to substrateD Inhibition is not reversed with substrate
14Factors that Affect Enzyme Efficacy TemperatureIncreases in temperature increase in molecular movement will speed up the rate of nonenzyme mediated reactions, and so temperature increase speeds up enzyme mediated reactions, but only to a point.When heated too much, enzymes (since they are proteins dependent on their shape) become denatured. When the temperature drops, the enzyme regains its shape.Thermolabile enzymes, such as those responsible for the color distribution in Siamese cats and color camouflage of the Arctic fox.Siamese cats: coat colours on the tips of the nose, ears and paws are darker colours at the tips of their bodies, where the temperature is slightly cooler, and the enzymes will thus only be active in these regions.Arctic Fox: in summer, the enzymes for white coat colour are denatured, then as the weather gets colder, the enzymes begin working and produce a white coat.
15…Factors that Affect Enzyme Efficacy Concentration of substrate and product also control the rate of reaction, providing a biofeedback mechanism.
16…Factors that Affect Enzyme Efficacy Changes in pH will also denature the enzyme by changing the shape of the enzyme.Remember: the shape of a protein (in this case, an enzyme determines its function). Enzymes are also adapted to operate at a specific pH or pH range.
17Enzyme InhibitionThere are a number of substances that can inhibit enzyme activity.Competitive Inhibitors are so similar to the enzyme’s substrate that they are able to enter the enzyme’s active site and block the normal substrate from binding.A drug, sulfanilamide resembles PABA, a chemical essential to a bacteria that infects animals. sulfanilamide competes with PABA, shutting down an essential bacterial (but not animal) pathways.enzymes