Download Chapter 12 Enzymes: The Protein Catalyst

Chapter 12 Enzymes: The Protein
Catalyst
Enzymes as Catalysts
• Enzymes are proteins that start chemical
reactions without being changed by the
chemical reaction
• Every enzyme is involved in a specific
chemical reaction
• Catalysts are substances that start a
reaction between substances without
being affected by the reaction
How Enzymes Work
• Most chemical reactions in the body need
additional energy to begin its process
• Activation energy is the energy needed to
begin a chemical reaction
• Enzymes start these chemical reactions by
lowering the activation energy required to
start the chemical reactions
How Enzymes Work
• Digestion- Without enzymes, the amount
of heat energy necessary to digest food
would destroy body organs
• Enzymes are very specific and will only
react with certain compounds
Enzymes and Substrates
• A substrate is the substance on which an
enzyme acts in an enzymatic reaction
• An active site is the location where the
substrate attaches to the enzyme
• There are two models used to illustrate
enzymatic reactions; the lock and key
model and the induced fit model
Coenzymes
• There are many enzymatic reactions that
require coenzymes
• Coenzymes are substances that must be
present for an enzymatic reaction to occur
• Three ways that coenzymes work;
• 1. A coenzyme attaches to an enzyme in a
way that changes the shape so that a
substrate will fit at the active site
Coenzymes
• 2. A coenzyme attaches to a substrate so
that the shape is changed to where it will
fit at the active site of the enzyme
• 3. The coenzyme is a transfer agent that
accepts an atom or molecular group from
a substrate and transfers it to another
compound
• Vitamins and minerals are important
coenzymes in food science
Naming Enzymes
• Nomenclature- naming system
• The naming system for enzymes is based
on the names of the substrates on which
enzymes act
• Most enzymes have the suffix –ase
• Digestive enzymes are commonly studied
by food scientists and are divided into
three main categories
Factors that Affect Enzyme Activity
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1. Water availability
2. Concentration of the solution
3. Factors that denature enzymes
A. Heat
B. pH or acids and bases
C. Electrolytes
Water Availability
• Water needs to be present to act as a
solvent in enzymatic reactions
• Water allows large molecules to be broken
down into smaller molecules
• Without water, molecules that break apart
can rejoin and there will be no net reaction
Concentration of the Solution
• The higher the concentration of substrate
in a solution, the greater the rate of
reaction will be
• A low concentration of substrate results in
a very slow rate of reaction
Factors that Denature Enzymes
• Since enzymes are proteins, they can be
denatured which changes the shape of the
enzyme and stops enzymatic activity
• A. Heat- An increase in temperature up to a
point increases enzymatic reaction rates but
eventually too much heat will cause the enzyme
reactions to cease
• Blanching- briefly purging food in boiling water to
stop enzyme activity; ex. Frozen vegetables
Factors that Denature Enzymes
• Meat tenderizers will work until heat is
added and then they will stop working
• B. pH- Every enzyme has a specific pH
range in which they react rapidly and a pH
where they will denature as well
• C. Electrolytes- electrolytes are positively
and negatively charged ions in solution.
High concentrations can either inhibit or
promote enzymatic activity
Factors that Denature Enzymes
• C. ex- Salt used to preserve meats by
inhibiting enzyme activity that would lead
to spoilage; mercury and lead poisoning
• Enzyme inhibitors- any substance that will
prevent the enzyme-substrate complex
from forming
• They are found in many plants and serve
as defensive mechanisms to kill fungi and
bacteria that might attack it
Enzymes and the Food Supply
• There are three ways that the food
industry uses enzymes to develop food
products
• 1. Enzymes are used to convert one food
product into another. Ex. Convert milk into
cheese
• 2. Enzymes extract food components from
food systems. Ex. Pectinase speeds up
the separation of juice from fruit residue
Enzymes and the Food Supply
• 3. Enzymes can help develop new foods
and ingredients. Ex. Lipases convert palm
oils into cocoa butter and beef fat into oleic
acid, which is used to make margarine