Lab Notes and Procedures-05 Biology 1004

North Arkansas College

Topic: Enzymes

1. An enzyme is an organic catalyst of biological origin that enters into and speeds up chemical reactions. It is not used up in the reaction.
2. E & S »» E – S » P & E

E = substrate, E – S = enzyme-substrate complex, P = product.

3. Enzymes are extremely specific for their substrate due to the active sites on the enzyme. Active sites combine with a particular (specific) substrate in a "lock & key" reaction. A substrate is anything that is acted upon by an enzyme.
4. An enzyme acts by lowering the activation energy of the reaction. Activation energy is the energy that is required to form chemical bond reactants. The enzyme and substrate comprise reactants.
5. There are component parts of an enzyme:

6. There are several factors that influence rate of enzyme reactions.

Concentration of Enzyme

The rate of reaction increases with increasing amounts of enzyme up to the point at which all of the substrate is combined with active sites (all used up).

The rate of the reaction increases as the concentration of the substrate increases up to the point at which all of the active sites are saturated.

Enzymes work optimally near neutral (pH 6.5-7.5). They are usually stable over a pH range of pH 4-9. Some, such as pepsin are stable and active at an acidic pH 1-3. Others are active at an alkaline pH in excess of pH 10 (detergents, drain cleaners).

Enzymatic reactions are chemical reactions, and chemical reactions tend to increase/speed up with increasing temperatures (from room temperature - 20-23°C, up to 37°C à which causes a faster reaction). Too high or low a temperature will impede enzyme reactions. Cold temperatures slow down chemical reactions. Very high temperatures can destroy the enzyme structure and its activity.

Experiment - Rennin: Rennin, an enzyme found in the stomach of cows and calves, is designed to coagulate milk for removal. It is also used to make cheese. This experiment is designed to look at the effect of temperature on rennin.

Use three tubes marked at 2 cm level.

Experiment - Urease: This experiment is designed to test the effect of enzyme concentration on urease. Urea has pH indicator built into it (cresol red) that turns yellow at acidic pH and red at an alkaline pH.

Experiment - Catalase: Catalase is an enzyme that is normally produced by living cells and breaks down peroxides. Peroxides are toxic to living systems.

Take 15 ml of H₂0₂ and bring up to 85 ml mark with distilled water (for 100 ml total concentration. Use 1 ml of blood (contains catalase).

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