Chapter 12: Enzymes: The Protein Catalyst Flashcards
Define an enzyme.
Specialized protein that speeds up or starts a chemical reaction without being changed by the reaction
What do enzymes allow?
Allows chemical reactions in the cells to happen fast enough to meet the body’s needs
What do enzymes facilitate?
Facilitates new product development
How many enzymes are in a cell?
Thousands of enzymes are in a cell, each having a unique function
Why do apples brown?
- Oxidation
- Cell damage (+ important)
Define a catalyst.
A catalyst is a substance that speeds up a reaction between substances without being affected by the reaction
What kind of substance are enzymes?
Group of proteins
How do we stop apples from browning?
- Lemon juice (will denature enzymes)
- Salt (will denature enzymes)
Why do cells only need a low concentration of many different enzymes?
Since enzymes do not change during chemical reactions
Define activation energy.
The energy needed to start a reaction
How do enzymes drive a reaction?
By lowering the amount of energy needed to start a reaction
What do digestive enzymes do?
Digestive enzymes decrease the amount of heat energy needed during digestion
Are enzymes specific?
Yes, enzymes are specific to the compounds with which they will react
Define the key and keyhole in the lock and key model.
- The key represents the substance being changed, known as the substrate
- The keyhole, or active site, is where the substrate attaches to the enzyme.
- The key must be inserted in the RIGHT spot in the right way
Why is the lock and key model limited? What does research indicate?
That the substrate does not turn when inserted into the active site and an enzyme is not a perfect match to the substrate
Name the 2 types of enzymatic models.
1) The lock and key model
2) The induced fit model
What does the induced-fit model address?
the limitations of the lock-and-key model
Define the induced-fit 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
Explain the basic process for enzymatic reactions.
1) Enzyme and substrate combine to form an enzyme-substrate complex
2) Enzyme-substrate complex is unstable and breaks apart, leaving the enzyme to act again on another substrate
Name 2 ways coenzymes work.
– 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
How do coenzymes work?
acting as a transfer agent by accepting an atom or molecular group and transferring it to another compound
Name important coenzymes.
- Vitamins and minerals
- the B vitamins, calcium, magnesium, and zinc
When was enzyme nomenclature accepted?
in 1961
Some enzymes had already been identified before the new naming system
How are enzymes named?
enzymes are named for the types of reactions or substances for which they are the catalyst
The ____ name for the enzyme and the _____ are the same
root, substrate
What is the suffix for enzymes?
-ase
Name the 3 categories of digestive enzymes.
– Proteases break apart proteins
– Lipases break apart lipids
–Carbohydrases break apart starches and sugars
Do enzymes only have one name?
- Some enzymes have more than one name
Given an example of an enzyme that has more than one name.
Sucrase is also known as invertase because the mixture of glucose and fructose is often called invert sugar
Name 6 factors that affect enzyme activity.
1) Water availability
2) Concentration of the solution
3) Temperature
4) Acids and bases
5) Electrolytes
6) Enzyme inhibitor
How does water availability affect enzyme activity?
Water must be available to act as a reactant as well as a solvent in enzymatic reactions
What does the lack of water do to enzymatic activity?
Slows or stops it
Will enzymatic reactions occur in dry products?
no
Water must be a reactant in what reaction?
Breakdown of carbs, lipids and proteins
How does the concentration of the solution affect enzyme activity.
The more substrate in the solution, the greater
the rate of reaction is
The rate of the enzymatic reaction increases as concentration increases, up till where?
The saturation point
How does heat affect enzyme activity? Give an example.
- heat increases enzyme activity
- ex: blanching vegetables before freezing
How does pH affect enzyme activity?
A pH that is too high or too low will denature
an enzyme
How do electrolytes affect enzyme activity?
can prevent enzymes from reacting with a
substrate
How do enzyme inhibitors affect enzyme activity?
prevents enzyme-substrate complexes from forming
How do enzyme inhibitors act?
change the shape of the enzyme or the
substrate
How do enzyme inhibitors protect foods?
Protect from bacteria and mold by stopping the digestive enzymes they release from working
Where do enzyme inhibitors occur?
They occur naturally in a wide variety of foods from animal and plant sources
Name 3 ways enzymes are used by the food industry to develop new products.
– 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
Name 4 positive effects of enzymes in the food supply.
– make food easier to eat
– preserve food
– improve flavor, quality, or appearance
– plays a role in fermentation
Name 3 negative effects of enzymes in the food supply.
– break down the structure of fruits and vegetables
– unpleasant flavor and odor changes
– undesirable changes in texture and color
How are carbohydrases used commercially?
react with sugars and starches for commercial uses.
Name 4 products of carbohydrases in food production.
– make corn syrup and high-fructose corn syrup
– ferment wine and beers – stabilize chocolate syrup – clarify fruit juices
Name 2 ways lipases are used in food production.
– 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
Name 5 ways proteases are used in food production.
– 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
What do oxidases do?
Deteriorate ripe fruits and vegetables when stored in an oxygen environment (must be stored in oxygen-free)
In what products would enzymatic browning be desirable? In what products would they be undesirable?
- Desirable: raisins, figs
Undesirable: sliced apples or pears
How does the food industry prevent browning of cut fruit?
Uses acids as enzyme inhibitors
How can the primary structure of proteins be destroyed?
Proteases
Why does sodium hydroxide make an apple brown?
It is oxidizing (there is oxygen)
