Enzymes: The Protein Catalyst Chapter 12 Enzymes: The Protein Catalyst

Objectives Describe the relationship between a substrate and an active site in enzymatic reactions. Identify the role of coenzymes in enzymatic reactions. List factors that affect enzymatic activity. continued

Objectives Explain how some foods are developed as a result of enzymatic activity. Demonstrate how to prevent enzymatic browning of foods.

Enzymes An enzyme is a specialized protein that speeds up or starts a chemical reaction without being changed by the reaction allows chemical reactions in the cells to happen fast enough to meet the body’s needs facilitates new product development Thousands of enzymes are in a cell, each having a unique function

Enzymes are Specialized Catalysts A catalyst is a substance that speeds up a reaction between substances without being affected by the reaction Enzymes are a group of proteins that act as catalysts Since enzymes do not change during chemical reactions, cells only need a low concentration of many different enzymes continued

Enzymes are Specialized Catalysts Activation energy is the energy needed to start a reaction Enzymes lower the amount of energy needed to start a reaction Digestive enzymes decrease the amount of heat energy needed during digestion Enzymes are specific to the compounds with which they will react

How Enzymes Work The lock-and-key model The enzyme is compared to the key of a lock The lock represents the substance being changed, known as the substrate The key must be inserted in the right spot in the right way The keyhole, or active site, is where the substrate attaches to the enzyme continued

How Enzymes Work The lock-and-key model is limited by research indicating that the substrate does not turn when inserted into the active site and an enzyme is not a perfect match to the substrate continued ©Goodheart-Willcox Publisher

How Enzymes Work The induced-fit model addresses the limitations of the lock-and-key model The active site temporarily changes the shape of the enzyme to allow the reaction to occur, then returns to its original configuration after the reaction continued ©Goodheart-Willcox Publisher

How Enzymes Work All enzymatic reactions follow the same basic process Enzyme and substrate combine to form an enzyme-substrate complex Enzyme-substrate complex is unstable and breaks apart, leaving the enzyme to act again on another substrate

Coenzymes Coenzymes work by attaching to the enzyme and changing its shape so the substrate can fit in the active site attaching to the substrate and changing its shape so it will fit the active site of the enzyme continued ©Goodheart-Willcox Publisher

Coenzymes Coenzymes work by acting as a transfer agent in accepting an atom or molecular group that is broken off and transferring it to another compound Vitamins and minerals are important coenzymes including the B vitamins, calcium, magnesium, and zinc

Naming Enzymes The nomenclature, or naming system, for enzymes accepted in 1961 confirmed that enzymes are named for the types of reactions or substances for which they are the catalyst the root name for the enzyme and the substrate are the same enzymes end in –ase Some enzymes had already been identified before the new naming system continued

Naming Enzymes The 3 categories of digestive enzymes Proteases break apart proteins Lipases break apart lipids Carbohydrases break apart starches and sugars Some enzymes have more than one name Sucrase is also known as invertase because the mixture of glucose and fructose is often called invert sugar

Factors That Affect Enzyme Activity Water availability Water must be available to act as a reactant as well as a solvent in enzymatic reactions The lack of water slows or stops enzymatic activity Enzymatic reactions will not occur in dry products Water must be a reactant in the breakdown of carbohydrates, lipids, and proteins continued

Factors That Affect Enzyme Activity Concentration of the solution The more substrate in the solution, the greater the rate of reaction is The rate of enzymatic reaction increases as the concentration increases, up to the saturation point Temperature Heat increases enzyme activity, as in blanching vegetables before freezing continued

Factors That Affect Enzyme Activity Acids and bases A pH that is too high or too low will denature an enzyme Electrolytes can prevent enzymes from reacting with a substrate Enzyme inhibitor prevents enzyme-substrate complexes from forming

Enzyme Inhibitors Enzyme inhibitors can change the shape of the enzyme or the substrate help protect foods from bacteria and mold by stopping the digestive enzymes they release from working They occur naturally in a wide variety of foods from animal and plant sources

Enzymes and the Food Supply Enzymes are used by the food industry to develop food products by converting one food product into another, such as with milk into cheese extracting food components from food systems such as the separation of juice from insoluble residues playing a key role in developing ingredients continued

Enzymes and the Food Supply Positive effects Negative effects make food easier to eat preserve food improve flavor, quality, or appearance plays a role in fermentation break down the structure of fruits and vegetables unpleasant flavor and odor changes undesirable changes in texture and color

Carbohydrases in Food Production Carbohydrases react with sugars and starches for commercial uses such as to make corn syrup and high-fructose corn syrup ferment wine and beers stabilize chocolate syrup clarify fruit juices ©2happy /Shutterstock.com

Lipases in Food Production Lipases are used to extract unwanted egg yolk from egg white to improve the whipping properties of egg white improve flavor and texture of various products including cheese, ice cream, margarine, butter, and many baked goods

Proteases in Food Production Proteases are used to tenderize meat by breaking long protein fibers, as in solutions for marinated meat reduce the size of proteins extracted from malt and grains during beer and ale production reduce mixing time increase pliability of dough change food into a different product, such as milk into cheese

Controlling Enzymatic Reactions Researchers consider enzyme reactions when determining how to preserve food Ripe fruits and vegetables are stored in an oxygen-free environment to prevent deterioration by oxidases Color changes from enzymatic browning may be desirable for raisins or figs, but not sliced apples or pears continued

Controlling Enzymatic Reactions To prevent browning of cut fruit, the food industry uses acids as enzyme inhibitors develops compounds from other sources, such as soy ©USDA

Recap In most biochemical reactions, enzymes are involved A substrate attaches to an enzyme at the active site Coenzymes help an enzymatic reaction occur by changing the shape of the enzyme or substrate acting as a transfer agent continued

Recap Enzyme activity is affected by water availability concentration of the solution heat acids and bases enzyme inhibitors electrolytes continued

Recap Enzymes produce both positive and negative effects during food production Enzymatic browning occurs when delicate cut fruit is exposed to oxygen This can be prevented by adding an acid, such as lemon juice, to act as an enzyme inhibitor