Enzymes

The purpose of an enzyme in a cell is to allow the cell to carry out chemical reactions

very quickly

What are enzymes?• Enzymes are made from amino acids

• They are proteins.

• An enzyme acts as a very efficient catalyst for a specific chemical reaction.

• The enzyme speeds that reaction up tremendously.

How are enzymes made?

• An enzyme is made by stringing together between 100 and 1,000 amino acids in a very specific and unique order.

• The chain of amino acids then folds into a unique shape.

• That shape allows the enzyme to carry out specific chemical reactions

How enzymes work

Enzymes are biological catalysts

Enzyme Action:

• An enzyme binds a substrate in a region called the active site

• Only certain substrates can fit the active site

• Enzyme-substrate complex forms

• Substrate reacts to form product

• Product is released

• http://www.bbc.co.uk/education/asguru/biology/02biologicalmolecules/01proteins/11enzymes/index.shtml

Enzyme action

Enzyme Action

+ +

E + S ES complex E + P

S

P

P

S

• Enzyme reactions are reversible. Just like a key can open and lock a door, an enzyme can cause a reaction to proceed in either direction.

• Hence Enzymes can be anabolic or catabolic.

4 steps

There are four steps in the process of an enzyme working.

1. An enzyme and a substrate are in the same area.

2. The enzyme grabs onto the substrate with a special area called the active site

3. A process called catalysis happens.

4. The enzyme lets go. The substrate is now called the product.

Induced Fit Model

• Enzyme structure flexible, not rigid• Enzyme and active site adjust shape to bind

substrate• Increases range of substrate specificity• Shape changes also improve catalysis

during reaction

Enzyme Action: Induced Fit Model

E + S ES complex E + P

S

P

P

SS

Learning Check

A. The active site is(1) the enzyme(2) a section of the enzyme(3) the substrate

B. In the induced fit model, the shape of the enzyme when substrate binds(1) Stays the same(2) adapts to the shape of the substrate

Can we stop them?

• There are many factors that can regulate enzyme activity, including

• temperature,

• activators,

• pH levels,

• inhibitors.

Temperature

• Proteins change shape as temperatures change.

• Enzyme activity is based on its shape

• Temperature changes means the enzyme won't work.

Temperature

• Little activity at low temperature• Rate increases with temperature• Most active at optimum temperatures

(usually 37°C in humans)• Activity lost with denaturation at high

temperatures

Temperature Affects Enzyme Action

Optimum temperature

ReactionRate

Low High

Temperature

pH Levels

• In the same way temperature changes the shape of proteins, the acidity or pH of the environment does the same thing.

• An increased acidity near an enzyme can cause its shape to change.

• The enzyme could unravel and become totally ineffective.

Factors Affecting Enzyme Action: pH

• Maximum activity at optimum pH

• Narrow range of activity

• Most lose activity in low or high pH

Factors Affecting Enzyme Action

Reaction

Rate

Optimum pH

3 5 7 9 11

pH

Substrate Concentration

• Increasing substrate concentration increases the rate of reaction (enzyme concentration is constant)

• Maximum activity reached when all of enzyme combines with substrate

Factors Affecting Enzyme Action

Maximum activity

Reaction

Rate

substrate concentration

Activators:

• Sometimes you need an enzyme to work faster and your body creates an activator.

• Other times you might eat something that acts as an activator.

• Activators make enzymes work harder and faster. If you're running in a race and you need more energy, get those enzymes to work!

Activators

Inhibitors

• These are the opposite of activators. • Inhibitors either slow down or stop the

activity of an enzyme. • They often bond to the protein, changing

the overall shape of the enzyme.• A nasty example of an inhibitor is snake

venom or maybe nerve gas from World War I.

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

Inhibitors

Learning Check

Sucrase has an optimum temperature of 37°C and an optimum pH of 6.2. Determine the effect of the following on its rate of reaction

(1) no change (2) increase (3) decrease

A. Increasing the concentration of sucrose

B. Changing the pH to 4

C. Running the reaction at 70°C

Examples of Enzymes

Proteases and peptidases –• A protease is any enzyme that can break down

a long protein into smaller chains

• Peptidases break peptides down into individual amino acids.

• Proteases and peptidases are often found in laundry detergents

• They help remove stains from cloth by breaking down the proteins.

Examples of Enzymes

Amylases –

• Amylases break down starch chains into smaller sugar molecules.

• Saliva contains amylase

• Maltase, lactase, sucrase finish breaking the simple sugars down into individual glucose molecules

Action of Maltase

Maltose is made of two glucose molecules bonded together (1).

The maltase enzyme is a protein that is perfectly shaped to accept a maltose molecule and break the bond (2).

The two glucose molecules are released (3).

Other Enzymes

Lipases - Lipases break down fats

Cellulases - break cellulose molecules down into simpler sugars.

• Bacteria in the guts of cows and termites excrete cellulases

• This is how cows and termites are able to eat things like grass and wood.

Bioprocessing• This is the use of enzyme-controlled

reactions to produce a product.• Bioprocessing traditionally used micro-

organisms such as yeast or bacteria to produce products like cheese, yoghurts and alcohol.

• Nowaday bioprocessing has developed to produce drugs, antibiotics, vitamins etc.

• How they produced these products was they placed the substrate & enzyme into 1 vessel and let the reactions occur.

Immobilised Enzymes

• Are enzymes that are attached or fixed to each other or an inert material.

• Enzyme = sucrase fixed to sodium alginate

• Advantages– Efficiency not effected– Can be recovered– Can be reused– Increases stability

Uses of Immobilised enzymes

• Soft drinks– Glucose Fructose – Enzyme used is Glucose Isomerase

• Penicillin– Penicillin New antibiotic– Enzyme used is penicillin acylase– Very expensive

• Lactase– Lactose Sweeter Sugars– Enzyme used Lactase– Very Expensive

Denaturation

• When most proteins are heated over 40oc they gradually lose their shape.

• Enzymes are made up of proteins if they lose their shape they cannot carry out reactions

Enzymes Extended Study

The Active Site

• The Active site is the part of the enzyme that combines with the substrate

• Contrary to belief the active site is not a rigid shape that is fixed to fit the substrate

• When the substrate enters the active site it causes it to change shape slightly

• The enzyme then fits more precisely around the substrate this is known as the Induced Fit model of enzyme action

The Bean Bag Theory!

• The induced fit model can be compared to the way a bean bag will adapt to fit snugly around our body shape when we sit in it

Mechanism of Enzyme action (Induced fit model)

1. The substrate combines with the active site of the enzyme

Active Site

Substrate

Enzyme

2. The active site is induced or caused to change shape slightly

Active Site

Substrate

Enzyme

3. The substrate and enzyme form an enzyme substrate complex

• The bonds in the substrate are altered so that the substrate changes into the products

Enzyme Substrate complex

Substrate changed to products which are released

4. The products leave the active site. The active site returns to its original shape and

is ready for a new substrate molecule

Active Site

New Substrate

Enzyme

Products

Learning Check

• Can you describe how enzymes and their substrates fit together?

• What is this model of enzyme action called?

• Can the enzyme work on more substrate once the products have been formed?

Optimum Conditions

• Optimum temperature refers to the temperature at which the enzyme will work best

• Optimum pH refers to the pH at which the enzyme will work best and so on

• What do you think body enzyme’s optimum temperature is?

Denaturation

• When most proteins are heated above 40 C or treated with certain chemicals or ⁰radiation they will gradually lose their 3 dimensional shape

• This means they will not be able to form the enzyme / substrate complex

• How does heat denature an enzyme?

• Can you give an example of this?

Learning Check

• What is meant by Optimum?

• What do you think the optimum temperature is for most body enzymes is?

Syllabus Can you?.....

• Explain the active site theory to examine enzyme function & specificity.

• Explain the term optimum activity with reference to temperature.

• Explain the nature of heat denaturation