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Enzymes

Enzyme and Digestion film clip

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What Are Enzymes?

• Most enzymes are Proteins

• Act as Catalyst to accelerates a reaction

• Not permanently changed in the process

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Enzymes• Are specific

for what they will catalyze

• Are Reusable• End in –ase

-Sucrase-Lactase-Maltase

- Lipase - Protease

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How do enzymes Work?

Enzymes work by weakening bonds which lowers activation energy

Enzymes Lower a Reaction’s Activation Energy

Activation Energy = energy needed to start a chemical reaction

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Enzymes

FreeEnergy

Progress of the reaction

Reactants

Products

Free energy of activationFree energy of activation

Without Enzyme

With Enzyme

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Enzyme-Substrate Complex

The substance (reactant) an enzyme acts on is the substrate

EnzymeSubstrate Joins

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Active Site

• An Active site of an enzyme molecule is where the substrate binds.

EnzymeSubstrate

Active Site

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Two ways in which Enzyme and substrates bind

•1. Lock and key model

•2. Induced fit model

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Lock and Key Model

+ +

E + S ES complex E+ P

S

P

P

S

E = Enzyme S = Substrate P= product

Active site

Lock & Key Model

•One enzyme

•for every substrate

•unique fit

Substrate

Enzyme

The enzyme fits over the substrate perfectly – like a key fits a lock.

It holds the starch molecule in place as a water molecule breaks the bond between two glucose particles

Starch molecule

Amylase enzyme

This continues until the molecule has been broken down completely

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Induced Fit• A change in

the shape of an enzyme’s active site

• Induced or altered by the substrate

The active site of an enzyme is where substrate is bound.

Many Enzymes Work by Altering the Shape of Their Substrates

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Enzyme Action: Induced Fit Model

• Enzyme structure flexible, not rigid

• Enzyme and active site adjust shape to bind substrate

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Enzyme Action: Induced Fit Model

E + S ES complex E + P

S

P

P

SS

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Factors Affecting Enzyme Activity

•Temperature•pH•Cofactors & Coenzymes

•Inhibitors

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Temperature & pH•High temperatures are the

most dangerous reactions & denature enzymes (Most like normal Body temperatures)

•Most enzymes like near neutral pH (6 to 8)

•Denatured (unfolded) by ionic salts and metal ions

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Factors Affecting Enzyme Action

Optimum temperature

ReactionRate

Low High Temperature

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Factors Affecting Enzyme Action

ReactionRate

Optimum pH

3 5 7 9 11pH

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Cofactors and Coenzymes

• Inorganic substances (zinc, iron) and vitamins (respectively) are sometimes need for proper enzymatic activity.

Example: Iron must be present in the

protein structure of hemoglobin in order for it to pick up oxygen.

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Factors Affecting Enzyme Action

Maximum activity

ReactionRate

substrate concentration

Digestive Enzymes

• There are 3 main types of digestive enzymes:– Amylase breaks starch down into

glucose.– Protease breaks protein down into

amino acids.– Lipase breaks fats down into fatty

acids and glycerol

Digestive Enzymes

Amylase

StarchGlucose

Protease

ProteinAmino Acids

Digestive Enzymes

Glycero

l

Fatty Acid

Fatty Acid

Fatty Acid

Glycerol

Fatty Acid

Fatty Acid

Fatty Acid

Lipase

Fat Fatty Acids and Glycerol

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Enzyme Inhibition

Inhibitors • Cause a loss of catalytic activity• Change the protein structure of

an enzyme• May be competitive or

noncompetitive• Some effects are irreversible• Poisons and drugs are

examples of enzyme inhibitors.

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Competitive Inhibition

A competitive inhibitor• Has a structure similar to

substrate• Occupies active site• Competes with substrate

for active site• Has effect reversed by

increasing substrate concentration

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Noncompetitive Inhibition

• Does not have a structure like substrate

• Binds to the enzyme but not active site

• Changes the shape of enzyme and active site

• Substrate cannot fit altered active site

• No reaction occurs• Effect is not reversed by adding

substrate