Images shutterstock.com Enzymes: The Protein Catalyst Chapter 12.

Images shutterstock.com

Enzymes:The Protein

Catalyst

Chapter 12

Permission granted to reproduce for educational use only.© Goodheart-Willcox Co., Inc.

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



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



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


Positive effects– make food easier

to eat– preserve food– improve flavor,

quality, or appearance

– plays a role in fermentation

Negative effects– break down the

structure of fruits and vegetables

– unpleasant flavor and odor changes

– undesirable changes in texture and color

Enzymes and the Food Supply


• 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

Carbohydrases in Food Production

©2happy /Shutterstock.com


• 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

Lipases 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

Proteases in Food Production


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


• 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

Recap

continued


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

Recap

continued


• 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

Recap

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