Design Activity Enzymes

Lactose (also called milk sugar) is a disaccharide found in milk only, and is an important source of energy for young mammals.

Lactase, secreted by mucosa and active in microvilli of epithelium of small intestine, with an optimum pH of 8.5 is an enzyme which breaks lactose into glucose and galactose.

Method and equipment:

In this experiment we are going to prepare 14 trials of lactase with lactose. In order to do that, we will need the following:

• a bottle of pills of enzyme lactase (can be bought at pharmacy)
• 700 millilitres of milk
• 7 test tubes
• Thermometer
• Stopwatch
• Measuring glass
• Lighter or any other source of fire

Variables:

• independent variable: temperature: 20°C,30°C,40°C,50°C,60°C,70°C,80°C.
• dependent variable: how much time is needed by the reaction to occur
• controlled variable: the same source of fire, stopwatch, test tubes, milk from the same source, pills of enzyme lactase from the same source

Instructions:

1. Using a measuring glass, pour to every test tube 100ml of milk.
2. Add four pills of enzyme lactase to every test tube.
3. Take first prepared test tube and put the thermometer into it. Switch on the stopwatch. Put the test tube close to the source of fire (carefully!) and heat until it reaches 20°C. Note, how much time it took for the pills to digest milk.
4. Repeat with another test tube, this time heating it to 30°C. Measure the time needed for the pills to digest milk.
5. Carry out the same experiment, heating test tubes one by one to the following temperatures: 40°C, 50°C, 60°C, 70°C, 80°C. Note your observations and time for every test tube.

Hypothesis:

As we know from biology lessons, the activity of enzymes is mostly affected by four main factors: pH, substrate concentration, enzyme concentration and temperature. In this investigation we are going to focus on temperature only and omit the rest of the factors.

It is known that most mammalian enzymes have a temperature optimum between 37-40°C. Therefore we can estimate that the milk will be most rapidly digested at the temperature of 40°C. At lower temperatures, the rate of the reaction will be lower, as the higher temperature, the higher rate of the reaction. Whereas at the temperatures higher than 40°C the enzyme may undergo a process called denaturation and will be no longer able to digest milk.