Proteins as Enzymes

1. Enzymes are proteins that that carry out most catalysis in living organisms 2. Unique three-dimensional shape enables an enzyme to stabilize a temporary association between substrates. The substrate fits into a specific place on the enzyme called an active site. 3. Because the enzyme itself is not changed or consumed in the reaction, only a small amount is needed, and can then be reused. 4. One Enzyme, one reaction. Enzymes are specific to the substrate.

5. Enzymes have specific names a. end in “ase”. b. Named according to the substrate they act on. c. Named according to the type of reaction they catalyze. Ex: DNA Ploymerase or Lipase

Enzymes Are Biological Catalysts catalyst –substance that lowers the activation energy, reactions proceed to products at a faster rate. Activation energy- refers to the extra energy required to destabilize existing chemical bonds and initiate a chemical reaction.

Energy supplied Activation energy Reactant Energy released Product Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Energy supplied Activation energy Reactant Energy released Product

Uncatalyzed Catalyzed Activation energy Reactant Product Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Uncatalyzed Catalyzed Activation energy Reactant Product

Enzyme Structure Most enzymes are quaternary with one or more active sites. Substrates bind to the enzyme at these active sites, forming an enzyme-substrate complex. With this binding, there is a slight change in shape of the complex, allowing close bonding and reactions to occur=

Copyright © The McGraw-Hill Companies, Inc Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Active site Enzyme

Copyright © The McGraw-Hill Companies, Inc Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Substrate

substrate complex. Products are Enzyme The substrate, Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. The substrate, sucrose, consists of glucose and fructose bonded together. 1 2 The substrate binds to the enzyme, forming an enzyme- substrate complex. Glucose Fructose Bond 4 Products are released, and the enzyme is free to bind other substrates. H2O Active site 3 The binding of the substrate and enzyme places stress on the glucose- fructose bond, and the bond breaks. Enzyme

Lego Enzymes

R1 B1 BL1 R3 G1 L1 Amino Acids B2 R2 W1 W2 W4 W3 substrate Active site Enzyme

Enzyme Forms A multi-enzyme complex is composed of several enzymes, catalyzing the different steps of a sequence of reactions, that are associated with one another. subunits work in concert, providing significant advantages in catalytic efficiency

Substrate Enzyme 1 Enzyme 2 Enzyme 3 Enzyme 4 Product

Factors Affecting Enzyme Activity Temperature Rate of an enzyme-catalyzed reaction increases with temperature, but only up to an optimum temperature or the enzyme denatures. Too low and the reaction is slowed down.

hotsprings prokaryote Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Optimum temperature for human enzyme Optimum temperature for enzyme from hotsprings prokaryote Rate of reaction 30 40 50 60 70 80 Temperature of reaction (°C)

pH Interactions hold enzymes together. If the pH is too high or too low they will be denatured.

Optimum pH for pepsin Optimum pH for trypsin Rate of reaction 1 2 3 4 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Optimum pH for pepsin Optimum pH for trypsin Rate of reaction 1 2 3 4 5 6 7 8 9 pH of reaction

Inhibitors and activators Inhibitor - substance that binds to an enzyme and decreases its activity competitive inhibitors –compete with the substrate for the same active site noncompetitive inhibitors – bind to the enzyme in a location other than the active site allosteric sites - specific binding sites acting as on/off switches

Factors Affecting Enzyme Activity activator - substances that bind to allosteric sites and keep the enzymes in their active configurations. *They can increase enzyme activity cofactors - chemical components that facilitate enzyme activity coenzyme *

Competitive inhibition Noncompetitive inhibition Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Substrate Competitive inhibitor interferes with active site of enzyme so substrate cannot bind Substrate Enzyme Enzyme Allosteric inhibitor changes shape of enzyme so it cannot bind to substrate Competitive inhibition Noncompetitive inhibition

Regulation of Biochemical Pathways Biochemical pathways must be coordinated and regulated to operate efficiently. advantageous for cell to temporarily shut down biochemical pathways when their products are not needed feedback inhibition When the cell produces increasing quantities of a particular product, it automatically inhibits its ability to produce more

No end-product inhibition Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Initial substrate Enzyme 1 Intermediate A Enzyme 2 Intermediate B Enzyme 3 End product No end-product inhibition