BIOLOGY

Protein Structure and Enzymes

What is an Enzyme?

Known as a BIOLOGICAL CATALYSTCatalyst is something that speeds up a

chemical reactionBiological catalyst speeds up reactions in

living cells

Activation Energy

Do this by lowering the ACTIVATION ENERGY - the energy required for a reaction to begin

Ene

rgy

Uncatalysed reaction

Catalysed reaction

What are the Properties of an Enzyme?

They are made of PROTEINThey are not changed by the reactions they

speed upThey are SPECIFIC- means that only one

particular enzyme will work with one particular substrate

They do this by lowering the activation energy.

They create a new reaction pathway “a short cut”

Terms you need to know

Enzyme helper molecule

Substrate molecule that enzymes work on

Enzyme-substrate complex enzyme & molecule

temporarily joinedActive site

part of enzyme that substrate molecule fits into

Naming Enzymes

Take the name of the substrate the enzyme works on and add the suffix -ase

Example: Lactose Lactase

Lock and Key ModelAll enzymes have a special shaped area that fits

onto their substrateThis area is called the ACTIVE SITEThis Active site will fit onto the substrate while the

reaction takes placeBecause it fits like a lock and key we call this the

lock and key mechanism Products have a different shape from the substrate Once formed, they are released from the active

site Leaving it free to become attached to another

substrate

Effect of Temperature

Speed of reaction increases until an Optimum temperature is reached

Optimum temperature is the temperature at which the enzyme works best

After this point the rate of reaction decreases until there is no reaction

At this point enzyme is said to be DENATURED – active site destroyed

pH and denaturation

Not all enzymes have the same “optimal” pH. Catalase (liver enzyme) is more like chymotrypsin. However, pepsin (a stomach enzyme) functions best at a low (acidic) pH. At pH 1, pepsin is in it’s functional shape; it would be able to bind to its substate. At pH 5, the enzyme’s shape is different and it no longer has an active site able to bind the substrate. The change in enzyme activity is observed as a difference in reaction rate.

Check Point!

How are Enzymes denatured?Answer: by change in temperature or pH