Enzymes

What are enzymes?  Chemically, enzymes are proteins.  They act as catalysts in chemical reactions.  The substances on which enzymes act are known as substrates.  Enzymes convert them into different molecules.  They catalyze chemical reactions by reducing their activation energy, thus increasing the rate of reaction.

Notes:  For a reaction to take place, these reactive sites have to be bought together.  This is where enzymes step in.  Because of its shape an enzyme has an area called the active site which can bring the reactive areas of two substrate molecules together.  The reactive site is a small area where it can react with other chemicals.  An enzyme-substrate complex is formed and the two chemicals react, joining together.

Lock and Key Model:

Induced Fit  In this model, when the substrate binds to the enzyme it may induce a change in the shape of the enzyme.  Once the product is released, the enzyme returns to its original shape.

Activation Energy Barrier:  A certain amount of energy is needed to get the reaction going.  Activation energy may also be defined as the minimum energy required to start a chemical reaction.  In the lab you can use heat to provide the energy, but a body uses enzymes, which lower the activation energy barrier.

Activation Energy Graph:

Denaturation of Enzymes:  Freezing does not affect enzyme activity whereas heating denatures the enzyme.  Denaturing enzymes can be either permanent or reversible.  Reversible denaturation occurs if you add a chemical such as urea. It will temporarily change the enzymes shape.  Irreversible denaturing takes place with heat. It breaks the covalent bonds in the protein.

Activity:  Summarise the notes on ‘Enzymes and the factors that affect them’ on page of Patterns of Life.

Enzyme Action: (pg 89 L.S.)  Aim: To investigate the effect of temperature on enzyme action.  Notes: Hydrogen peroxide is a poisonous substance produced during cell respiration. Fortunately cells contain an enzyme peroxidase that very rapidly breaks down hydrogen peroxide into water and oxygen.  2H 2 O 2  2H 2 O + O 2

 Method:  Drop a little ground up raw liver into a test tube containing 5% hydrogen peroxide.  Use a glowing splint to test an gas given off. (Oxygen will cause a glowing splint to flare up.)  Repeat the activity with a piece of frozen and cooked liver.