Enzymes

Characteristics of Enzymes

1. Proteins

2. Catalystsa. Speed up chemical

reactions without being used up

How do enzymes work?

1. Lower Activation Energy to speed up rates of reactiona. Reactions require energy to begin…

enzymes lower the amount of energy required.

Naming

1. Often end in “–ase”

2. The name usually relates to the reactants they are associated with or the reaction they help start

a. Examples: maltase, sucrase,

protease, carboxypeptidase

Catalyzing Process

1. A unique 3-D shape of an enzyme determines which chemical reaction it catalyzes

2. Important Vocab:a. SUBSTRATE: A specific reactant that

an enzyme acts on is called a substrate of the enzyme.

2. Important Vocab (cont.):b. ACTIVE SITE: A substrate fits into a

region of the enzyme called an active site.1. An active site is typically a pocket or

groove on the surface of the enzyme.

3. The enzyme and substrate form a complex

substrate

enzyme

Active site

Enzyme-substrate complex

Lock and Key Model

+ +

E + S ES complex E + P

S

P

P

S

Structure1. If an enzyme’s shape is changed so that

it is no longer able to catalyze reactions, we call it…

DENATURED

– What kinds of things do you think could denature a protein?

Denaturation

a. Disruption of protein structure by1. Heat: Break apart H bonds and disrupt

hydrophobic attractions 2. Acids/ bases: Break H bonds between polar

R groups and ionic bonds3. Heavy metal ions: React with S-S bonds to

form solids4. Agitation: Stretches chains until bonds

break

Applications of Denaturation

a. Hard boiling an egg

b. Wiping skin with alcohol swab for injection

c. Cooking food to destroy E. coli

d. Heat used to cauterize blood vessels

e. Autoclave sterilizes instruments

f. Milk is heated to make yogurt

Think about it

Tannic acid is used to form a scab on a burn. An egg becomes hard boiled when placed in hot water. What is similar about these two events?

Solution

Acid and heat cause a denaturation of protein. They both break bonds in the structure of protein.

Factors Affecting Enzyme Action

1. Temperature affects molecular motion

a. An enzyme’s optimal temperature produces the highest rate

b. Most human enzymes work best at 35-40 ºC.

WATCH OUT!!!If the temperature gets too high, the enzyme may be

denatured!

Temperature (cont.)

Optimum temperature

ReactionRate

Low High

Temperature

2. Ions: Salt concentration & pH influence enzyme activity.

a. SALT: The salt ions interfere with some of the chemical bonds that maintain protein structure

b. pH: The same is true of the extra hydrogen ions at very low pH

1. Optimal pH for most enzymes near neutral

3. Substrate Concentrationa. Increasing substrate concentration

increases the rate of reaction (enzyme concentration is constant) Why?

b. Maximum activity reached when all of enzyme combines with substrate

Substrate Concentration (cont.)

Maximum activity

Reaction

Rate

substrate concentration

Enzyme Inhibition

1. Inhibitors: cause a loss of catalytic activity

a. May change the protein structure of an enzyme

b. May be competitive or noncompetitive

c. Some effects are irreversible

2. Competitive Inhibition

a. A competitive inhibitor1. Has a structure similar to substrate2. Occupies active site

a. “Competes” with substrate for active site

3. Effects can be reversed by increasing substrate concentration

Competitive Inhibition Image

3. Noncompetitive Inhibition

a. A noncompetitive inhibitor

1. Does not have a structure like substrate

2. Binds to the enzyme (not at active site) & changes the shape of enzyme & active site

a. Substrate cannot fit altered active site

3. No reaction occurs

4. Effect is not reversed by adding substrate

Noncompetitive Inhibition Image