Enzymes
Enzymes are usually more efficient than man-made catalysts operating under the same conditions. Because many enzymes with different specificities occur in a cell, each enzyme, must be very efficient. One molecule of the enzyme catalase, for example, can produce 10*12 molecules of oxygen per second.

Enzymes have a special affinity for the substrate. They fit together, matching in shape and charge. The part of the enzyme where the substrate fits, is called the active site. The amino acid residues in the active site are in the right 3D conformation to bind and modify the substrate.

The combination of substrate molecules with enzymes also involves collisions between the two. The substrate must reach the active site. As the substrates are used up during a reaction (converted to products), the chance of their colliding with the enzyme decreases, this results in a decrease in the amount of product being produced (reaction rate).

In this week's lab we will measure the rate of a reaction by measuring the amount of substrate remaining after some period of time. This is a little unusual. In our reaction, H2O2 is the substrate and H2O2 is converted to H2O + O2 as the reaction proceeds. Rather than measuring the formation of Product as an indicator of the reaction, we will measure the disappearance of substrate.

For instance:

• We start with 3 ml of H2O2 from your bathroom cabinet
• Added Catalase
• Wait three minutes
• Measure and find 1 ml of H2O2 remaining

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