Chapter 12: Enzymes: The Protein Catalyst

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

• Oxidation

- Cell damage (+ important)

A catalyst is a substance that speeds up a reaction between substances without being affected by the reaction

Group of proteins

• Lemon juice (will denature enzymes)

- Salt (will denature enzymes)

Since enzymes do not change during chemical reactions

The energy needed to start a reaction

By lowering the amount of energy needed to start a reaction

Digestive enzymes decrease the amount of heat energy needed during digestion

Yes, enzymes are specific to the compounds with which they will react

• 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

That the substrate does not turn when inserted into the active site and an enzyme is not a perfect match to the substrate

1) The lock and key model

2) The induced fit model

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

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

– 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

acting as a transfer agent by accepting an atom or molecular group and transferring it to another compound

• Vitamins and minerals

- the B vitamins, calcium, magnesium, and zinc

in 1961

Some enzymes had already been identified before the new naming system

enzymes are named for the types of reactions or substances for which they are the catalyst

root, substrate

-ase

– 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

1) Water availability
2) Concentration of the solution
3) Temperature
4) Acids and bases
5) Electrolytes
6) Enzyme inhibitor

Water must be available to act as a reactant as well as a solvent in enzymatic reactions

Slows or stops it

no

Breakdown of carbs, lipids and proteins

The more substrate in the solution, the greater

| the rate of reaction is

The saturation point

• heat increases enzyme activity

| - ex: blanching vegetables before freezing

A pH that is too high or too low will denature

| an enzyme

can prevent enzymes from reacting with a

| substrate

prevents enzyme-substrate complexes from forming

change the shape of the enzyme or the

| substrate

Protect 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

– 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

– 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

react with sugars and starches for commercial uses.

– make corn syrup and high-fructose corn syrup

| – ferment wine and beers – stabilize chocolate syrup – clarify fruit juices

– 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

– 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

Deteriorate ripe fruits and vegetables when stored in an oxygen environment (must be stored in oxygen-free)

• Desirable: raisins, figs

| Undesirable: sliced apples or pears

Uses acids as enzyme inhibitors

Proteases

It is oxidizing (there is oxygen)