MACROMOLECULES – PROTEINS

- ENZYMES

ENZYMES Enzymes are made up of proteins.

Enzymes act as a catalyst in living organisms.

A catalyst is a substance that speeds up chemical reactions.

SO, enzymes speed up chemical reactions that occur in living organisms.

ENZYMES The name of different enzymes always

ends in –ase. For example,

Maltase is an enzyme that breaks down the sugar maltose.

Lactase is an enzyme that breaks down the sugar lactose.

Sucrase is the enzyme that breaks down table sugar, sucrose, into fructose and glucose.

STRUCTURE OF AN ENZYME All enzymes have an active site. The active site is where the substrate

attaches to the enzyme. The substrate is the substance that the

enzyme is going to process.

CHEMICAL REACTIONS Chemical reactions consist of reactants

and products. Reactants change or react to form

something new called products.

With an enzyme, the reactants (or substrate) are converted into products, but the process happens in less time.

HOW DO ENZYMES WORK? The substrate (or reactants) attach to

the active site to become an enzyme-substrate complex.

The enzyme-substrate complex undergoes a chemical reaction to create new products.

The products are then released from the active site.

HOW DO ENZYMES SPEED UP CHEMICAL REACTIONS? All reactions require energy to be

carried out. The minimum amount of energy

required to start a reaction is called the activation energy.

Enzymes speed up a chemical reaction by lowering the minimum amount of activation energy needed to carry out a chemical reaction.

ACTIVATION ENERGY In the diagram, the red line is the

minimum energy needed for the reaction to occur without an enzyme.

The green line is the minimum energy needed for the reaction to occur with an enzyme.

The minimum amount of activation energy needed to get the reaction started is less with an enzyme present.

ENZYMES ARE SPECIFIC Enzymes complete very, very specific

jobs. They can only work with specific

molecules and only do specific tasks.

Enzymes are often referred to as a “lock and key” model: One key fits one lock. One substrate fits one

enzyme.

ENZYMES ARE REUSABLE Enzymes are very

specific, but they can be reused many times.

Once an enzyme has taken a substrate and converted it into new products, it can take in another substrate and convert it into new products as well.

An enzyme is reusable and can perform many reactions!

ENZYMES NEED CERTAIN CONDITIONS Enzymes function best in certain

conditions.

The 4 conditions that affect enzyme activity:1. Substrate Concentration2. Enzyme Concentration3. Temperature4. pH

SUBSTRATE CONCENTRATION If there isn’t enough substrate (or

reactants) present, then the enzyme cannot perform a chemical reaction.

In this diagram, 2 substrates are needed for the enzyme to work, but only 1 substrate is present, thus the reaction cannot happen.

ENZYME CONCENTRATION Alternatively, if there isn’t enough

enzyme present, then the substrates have nothing to bind onto and the chemical reaction cannot occur.

In this diagram, 2 substrates are available for the enzyme to work, but there isn’t an enzyme present, thus the reaction cannot happen.

The substrates have to wait until an enzyme becomes available.

TEMPERATURE Some enzymes become destroyed if

they do not have the most “optimum” or ideal conditions to work.

Extreme temperatures destroy or denature enzymes.

Too HOT can denature an enzyme. Too COLD can denature an enzyme. Each enzyme has an optimum or best

temperature for itself, but all enzymes are destroyed at HOT and COLD extreme temperatures.

PH Each enzyme also has a pH value that it

works the best in. Some enzymes prefer acidic conditions (0-6). Some enzymes prefer basic conditions (8-14). Some enzymes prefer neutral pH conditions (7).

For example, Pepsin a stomach enzyme, prefers an acidic pH level to optimally carry out reactions. This would make sense, since the stomach is a very acidic environment.

ENZYMES ARE REGULATED Enzymes are regulated, otherwise, they

would just keep performing chemical reactions whether they were needed or not.

Enzymes are regulated in 3 ways:1. Competitive Inhibition2. Noncompetitive Inhibition3. Feedback Inhibition

Inhibition means to prevent or stop.

COMPETITIVE INHIBITION Competitive inhibition regulates

enzymes. Another molecule that is similar in

shape, competes for the enzyme’s active site.

This other molecule becomes a block of the active site for the normal substrate.

The normal substrate can no longer bind onto the active site and thus the reaction cannot occur.

NONCOMPETITIVE INHIBITION Noncompetitive inhibition also regulates

enzymes. Another molecule, called an inhibitor,

binds to another site on the enzyme, called an allosteric site. This causes the enzyme to change the shape of its active site, so that the substrate can no longer bind on to the active site and carry out a reaction.

FEEDBACK INHIBITION Feedback inhibition is another way that

enzyme activity is regulated. The end product made by the enzyme

or enzymes, feeds back to the beginning and turns the enzyme off so that it stops making more product.