Passage VI

Enzymes serve as catalysts (compounds that increase the rate of a chemical reaction but are themselves not used up) during digestion. The enzyme trypsin is involved in the breakdown of proteins into smaller subunits during digestion. A student investigated the effects of temperature, incubation time, and pH on enzyme activity.

Experiment 1

To each of 11 test tubes, 6 milliliters (mL) of a casein (a protein) solution was added. One mL of a trypsin solution was added to each of Tubes 1–10. Tube 11 received 1 mL of water without trypsin. The tubes were then stirred in water baths at various temperatures, and incubated (heated) from 0 to 15 minutes (min). After incubation, 0.1 mL of CaCl₂ solution was added to each tube. CaCl₂ stops the reaction and forms a precipitate (solid) with the protein that is not broken down by the trypsin. The precipitates were removed from the tubes and dried. The masses of the precipitates, in milligrams (mg), were measured to determine the relative amount of protein that remained in each tube. The results are in Table 1.

Experiment 2

To each of 6 test tubes, 6 mL of casein solution and 1 mL of trypsin solution were added. Tubes were adjusted to various pHs. Each tube was stirred and incubated at 25°C for 10 min. The relative amount of protein present in each tube was determined as in Experiment 1. The results are in Table 2.