Catalase

ENZYME ACTIVITY

This activity is an alternative to the titration proposed for Enzyme Catalysis (AP Bio Lab #2,

Biology Lab Manual). There are numerous alternative lab activities that measure the rate of

enzyme activity (i.e. Gen Nelson, Catalase Lab, http://www.accessexcellence.org). This one

is Erol Altug’s, which has been modified from the one developed by Tom Carroll of St.

Alban’s School. The introduction and some questions are from Biology Lab Manual.

Introduction

Enzymes are biological catalysts that carry out thousands of chemical reactions, which

occur in living cells. They are generally large proteins made up of several hundred amino

acids, and often contain a non-proteinaceous group that is important in the actual catalysts.

In an enzyme-catalyzed reaction, the substance to be acted upon, the substrate, binds in the

active site of the enzyme. The enzyme and substrate are held together in an enzymesubstrate complex by hydrophobic bonds, hydrogen bonds, and ionic bonds.

The enzyme then converts the substrate to the reaction products in a process that often

requires several chemical steps, and may involve covalent bonds. Finally, the products are

released into solution and the enzyme is ready to form another enzyme-substrate complex.

As is true of any catalyst, the enzyme is not used up as it carries out the reaction, but it

recycled over and over. One enzyme molecule can carry out thousands of reaction cycles

every minute.

Each enzyme is specific for a certain reaction because its amino acid sequence is unique and

causes it to have a unique three-dimensional structure. The “business” end of the enzyme

molecule, the active site, also is specific so that only one or a few of the thousands of

compounds present in a cell can interact with it. If there is a prosthetic group on the

enzyme, it will form part of the active site. Any substance that blocks or changes the shape of the

active site will interfere with the activity and efficiency...