BIOLOGY Protein Structure and Enzymes

What is an Enzyme? Known as a BIOLOGICAL CATALYST Catalyst is something that speeds up a chemical reaction Biological catalyst speeds up reactions in living cells

Activation Energy Do this by lowering the ACTIVATION ENERGY - the energy required for a reaction to begin Energy Uncatalysed reaction Catalysed reaction

What are the Properties of an Enzyme? They are made of PROTEIN They are not changed by the reactions they speed up They 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 joined Active 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 Model All enzymes have a special shaped area that fits onto their substrate This area is called the ACTIVE SITE This Active site will fit onto the substrate while the reaction takes place Because 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