Aim: The aim is to determine the effect of temperature on the rate in which pepsin digests albumen.
Research Question: What is the effect of temperature on the rate in which the enzyme pepsin digests protein (albumen)?
Enzymes are globular proteins acting as catalysts of chemical reactions. An enzyme has an active site: region on the surface of an enzyme catalyzing a chemical reaction involving the substrates and to which substrates bind.
The active site of an enzyme has a unique shape; therefore, the enzymes can only catalyze certain reactions since solely substrates of the same size can fit. The enzyme is therefore specific to its substrate; consequently, the enzyme is seen as the “lock” and the substrate is the “key”.
Denaturation is the changing of the structure of an enzyme, which is thus unable to perform its function. This can occur due to an increase in temperature, since above a certain point, the enzyme denatures. The heat, which causes vibration, ruins its structure, as the bonds that hold the enzyme together breaks.
Other factors are going above the optimum pH level and an increase in substrate concentration to the point it will no longer have an effect on enzyme activity. Pepsin needs an acidic pH of around 2 to digest proteins.
Digestion refers to the chemical breakdown of large food molecules into smaller molecules. Pepsin is an enzyme in the digestive system, which help a person digest protein into amino acids for growth of cells in the body. This process is known as protein breakdown: the protein is broken down into polypeptides and released as amino acids.
When albumen, which is the protein contained in egg white, and pepsin are mixed together at the appropriate pH and temperature, the mixture will become clear. This signifies that the pepsin has digested the albumen.
I predict that by increasing the temperature, the rate of reaction will increase as well until it goes above the optimum temperature. Above the optimum temperature, the enzyme will denature. I predict that the optimum temperature will be around 40 degrees since digestion occurs at body temperature, which is approximately 37° C.
The independent variable is the temperature (10 °C, 20 °C, 30 °C, 40°C, 50°C, 60 °C, 70°C, 80°C)
The dependent variable is the time of reaction for the mixture to become clear, as this shows that that the albumen was broken down into amino acids, as they are colorless.
Temperature °C (10 °C, 20 °C, 30 °C, 40°C, 50°C, 60 °C, 70°C, 80°C)
Rate of reaction (time taken for the albumen solution to become clear)
i. Same quantity of albumen used for each temperature
ii. Same quantity of pepsin used for each temperature (5 cm3)
iii. Amount of hydrochloric acid (1 M)
iv. A universal indicator
v. Water bath
vi. Same timing
i. 8 × 5cm3 of albumen
ii. Electronic water bath
iii. 8 × 5cm3of pepsin
iv. 8 × 1M hydrochloric acid
vi. 2 × Fine ended dropping pipette
vii. Universal indicator paper
viii. 2 × Measuring cylinders of 10mL
ix. 1 thermometer
x. 1 test tube 18x150mm
xi. Safety goggles
xii. water bath
This procedure uses an enzyme and hydrochloric acid.
Wear safety goggles.
1) In a measuring cylinder, measure 5 cm3 of albumen using a pipette.
2) In another cylinder, measure 5cm3 of pepsin using another pipette.
3) Heat the water bath at 10 degrees Celsius for 4 minutes.
4) Use a thermometer to keep the temperature consistent.
5) Heat the two cylinders containing the albumen and pepsin separately in the water bath.
6) Add the pepsin and albumen together in a single test tube.
7) Using a dropping pipette, test the hydrochloric acid on universal indicator paper in order to assure it is PH 2, so that it is consistent for each temperature.
8) Using a dropping pipette, carefully add the 1M hydrochloric acid in the test tube.
9) Using a stopwatch, time the number of seconds it takes for the mixture to become clear, as this indicates when the reaction is over.
10) Repeat the experiment 3 times for reliability and then take the average time for accuracy of the results.
11) Repeat the experiment for the different temperatures used after washing the pipette and the test tubes.
Table showing the time taken to digest proteins at different values of the temperature
Time taken in minutes
A corresponding graph that shows the amount of time taken to digest the protein as per different temperature values
At lower temperatures, it takes more time for the solution to become clear. However, as the temperature increases the molecules begin to break hence gaining more kinetic energy. The optimum temperature is at 400C. As the temperature is further increased, the amount of time required for the complete digestion of proteins further increases. The best way to find out when the solution completely turns clear is to put a cross (X) at the base of the test-tube and determine when the cross can be clearly seen.
"My Favorite Protein." Pepsin. 04 Nov. 2012
"Click4Biology: 3.6: Enzymes." Click4Biology. 04 Nov. 2012
"National Digestive Diseases Information Clearinghouse (NDDIC)." - National Digestive Diseases Information ClearinghouseYour Digestive System and How It Works. 04 Nov. 2012