An introduction to their characteristics and role in a

biological world.

ENZYMES

All you need to know…

What is an enzyme?

•Enzymes are known as catalysts of chemical reactions – they allow reactions to speed up and to take place with less energy.

Many reactions would not take place without them.•Enzymes are proteins that are rounded in shape.

•We have come across enzymes studying digestion, their names usually end in ‘ase’ (like amylase) but don’t have to

(like pepsin).•Enzymes are very important to cells because they help

molecules to form, to breakdown, or to exchange parts. They are a vital for normal metabolism and occur in relatively small

numbers.Breaking down

Building up

What is the structure of an enzyme?

Molecular models of proteins show their complex 3D structure as such…

But we can represent them in 2D drawings for simplicity like this…

How does the enzyme break down

molecules?Enzyme

Substrate

The substrate

binds to the active site

of the enzyme

Active site A chemical reaction takes place at

the active site and the more complex molecule (substrate) is broken down into two simpler

forms (products). This takes place either inside the cell (intracellular

enzyme) or outside the cell (extracelluar enzyme i.e. the

digestive enzymes)

Products

How does the enzyme build up

molecules?Enzyme

Substrates

The substrates bind to the active site where a chemical reaction takes place. The two less complex molecules are metabolized into a

more complex molecule to be used within our bodies. The substrates are the reactants of the

chemical reaction.

Note that substrate and enzyme work like a lock and

key. But if the substrates don’t fit sometimes the

enzyme can slightly alter its shape to accommodate the substrate. This is known as

induced fit.

Product

How do enzymes exchange parts of

substrates?Amazing! One of the

phosphate groups from the ATP has moved to the glucose

molecule during this reaction. All these reactions mentioned so far release heat when they

take place.

Here’s some interesting facts about enzymes

•Enzymes are specific to their reaction. Their 3D shape gives them their specificity. Maltase cannot break down fat.•Enzymes do not get used up in the reaction so they can be used over and over again.•Enzymes need the right temperature to function properly. If conditions are too cold the enzyme won’t be active. If it is too hot they denature – that is their shape is destroyed beyond repair and hence the substrate won’t bind. What temperature do you think enzymes work best at in the human body?•They also need a suitable pH or they will denature. What pH do you think lipase works best in the stomach?

So how does temperature affect enzyme activity?

Lovely! You can see the temperature at

which this enzyme is the most active and

when it begins to denature.

So how does pH affect enzyme activity?

•Which enzyme functions the best in very acidic conditions?

•Which enzyme is denatured at a pH of 6?

Does substrate concentration affect the rate of a reaction?

You will notice that the more concentrated the substrate is,

the greater the rate of reaction – but only to a

certain point. The enzymes can only catalyze to a certain

rate and then they can’t function any more effectively.

Do enzymes reduce the amount of energy needed for

a reaction?

Yes, that is correct. The red line shows the energy needed – the

activation energy - for a reaction when an enzyme is used.

So if a reaction doesn’t use an enzyme to catalyze it, then it

actually requires more energy to take place?

Anything else we should know?

Sometimes an enzyme needs help from another molecule. If this molecule

is organic (such as a vitamin) it is known as a coenzyme. If the helper

molecule is inorganic (such as a mineral ion) it is known as a cofactor. If they don’t bind to the active site they

are known as allosteric. Here is a diagram showing either a coenzyme or a cofactor as it is binding to the active

site.

Anything else I should know?

What’s she saying?

Sometimes other substances can bind at

the active site and block the reaction.

Below us is an allosteric inhibitor – it does not use

the active site, but

changes its shape.

Shhhh!

Three cheers for enzymes!!

And here is one last example of how vital

these catalytic proteins are…

This will help when you study DNA replication

DNA ligase is the enzyme used to rejoin the new strands of DNA to the original template

when it replicates itself. Mmmnnn I didn’t realize just

how vital enzymes are.

The End!