# Question Video: Applying Knowledge of Enzyme-Controlled Reactions to Example Experiments Biology

A student is completing an experiment studying the rate at which trypsin, an enzyme found in the human body, breaks down proteins in a beaker of milk. They are running the experiment at 20°C with a pH buffer of pH 9. What chang in conditions would most likely speed up the rate of reaction? [A] Reducing the amount of light the reaction is exposed to [B] Decreasing the concentration of trypsin [C] Increasing the temperature to 37°C [D] Increasing the pH to 14

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### Video Transcript

A student is completing an experiment studying the rate at which trypsin, an enzyme found in the human body, breaks down proteins in a beaker of milk. They are running the experiment at 20 degrees Celsius with a pH buffer of pH nine. What changing conditions would most likely speed up the rate of reaction? (A) Reducing the amount of light the reaction is exposed to. (B) Decreasing the concentration of trypsin. (C) Increasing the temperature to 37 degrees Celsius. Or (D) increasing the pH to 14.

For an enzyme-catalyzed reactions such as this to take place, the substrate, in this case proteins, must physically collide with the enzyme. Therefore, any condition which increases the chances of the enzyme and substrate colliding will increase the rate of the reaction. There are four main changes in conditions that can do this. So let’s consider each one in the context of this reaction.

The first is to increase the concentration of the enzyme, which in this case is trypsin. The more trypsin molecules there are in the reaction, the more likely each protein molecule is to collide with one and therefore the higher the rate of reaction. This means we can rule out option (B) because it’s talking about decreasing the concentration of trypsin, which would actually have the opposite effect and decrease the rate of reaction.

The second change is to increase the concentration of the substrate, which in this case is protein. This works in the same way as increasing the trypsin concentration. The more protein molecules there are in a reaction, the more they will collide with trypsin molecules and the higher the rate of reaction. The third is to change the pH, which is how acidic or alkaline the conditions are. You may recall that pH is measured on a scale from one to 14, where pH one represents a very acidic environment and pH 14 represents a very alkaline environment. pH seven represents a neutral environment, which is neither acidic nor alkaline.

All enzymes have an optimum pH. This is the pH at which the enzyme catalyzes its chemical reaction at the highest rate. The further away the conditions are from the optimum pH, the slower the rate of reaction. Because most body cells have a neutral pH of around seven, most enzymes have an optimum pH of around seven too. For the experiment carried out in the question, we’re told that a pH buffer of pH nine is used. We can therefore also rule out option (D) because it suggests increasing the pH to the most alkaline value of 14. Any substantial change in pH like this is likely to inhibit the enzyme’s activity and would therefore decrease the rate of reaction.

We can also rule out option (A) because although there are a few examples of enzymes in the human body which are sensitive to light, it’s very dark inside the digestive system where trypsin is active. So it’s highly unlikely to respond to changes in light intensity.

The final changing conditions which will increase the rate of an enzyme-catalyzed reaction is to increase the temperature. At higher temperatures, both enzyme and substrate molecules have more kinetic, or movement, energy. Meaning they will collide more often because they’ll be moving around more and the rate of reaction will therefore be higher. Humans have an average body temperature of 37 degrees, so most enzymes in the human body, including trypsin, will be adapted to work best at this temperature. Therefore, increasing the temperature from 20 degrees up to 37 degrees will be very likely to speed up the rate of the reaction. We can therefore conclude that the correct answer is (C). Increasing the temperature to 37 degrees would be most likely to speed up the rate of reaction.