2. Enzymes: The Protein Catalyst
Chapter 12
Enzymes: The Protein Catalyst

3. 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.
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4. Objectives
Explain how some foods are developed as a result of enzymatic activity.
Demonstrate how to prevent enzymatic browning of foods.

5. 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

6. 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
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7. 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

8. 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
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9. 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
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10. 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
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11. 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

12. 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
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13. 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

14. 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
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15. 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

16. 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
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17. 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
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18. 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

19. 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

20. 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
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21. 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

22. 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
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23. 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

24. 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

25. 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
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26. 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

27. 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
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28. Recap Enzyme activity is affected by water availability
concentration of the solution
heat
acids and bases
enzyme inhibitors
electrolytes
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29. 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