Optimal Enzyme Conditions - Online Tutor, Practice Problems & Exam Prep

Enzymes require specific conditions for optimal activity, including optimal pH and temperature. Most enzymes, being proteins, are sensitive to pH changes that can alter the charges of amino acids in their active sites, potentially hindering catalysis and leading to denaturation. For example, pepsin operates best at a pH of 1.5 in the acidic stomach, while chymotrypsin functions optimally at pH 8 in the small intestine. Additionally, human enzymes thrive at around 37°C, reflecting body temperature, whereas thermophilic bacterial enzymes are adapted to higher temperatures, around 77°C, in extreme environments.

Optimal Enzyme Conditions

In this video, we're going to talk about optimal enzyme conditions. It turns out that proper enzyme catalysis requires a very specific set of conditions, including a very specific pH and a very specific temperature. Moving forward, we're first going to focus on optimal pH, and then later in our next video, we'll focus on the optimal temperature. We know that most enzymes have an optimal pH that allows them to display their greatest amount of activity. Most enzymes are proteins, and both enzymes and proteins are sensitive to pH; different enzymes have their own optimal pH. Why are enzymes sensitive to the pH? Recall from our previous lesson videos that the charges of ionizable amino acids actually vary with pH. pH changes could cause active site amino acids to change their charges. The charges of amino acids in the active site could potentially be super important for enzyme catalysis. If we change those charges, then we could potentially hinder enzyme catalysis. Later in our course, we'll talk more about enzyme catalysis when we discuss different types of enzyme catalysis. For now, all you need to know is that the charges of amino acids are not only potentially important for enzyme catalysis but also for maintaining protein structure, specifically the tertiary and quaternary structure. By changing the pH significantly enough, that could cause the enzyme to denature. If we denature the entire enzyme, enzyme catalysis will definitely be hindered.

In our example below, it's asking us, what is the approximate optimal pH for pepsin and for chymotrypsin? Pepsin's curve is in black, and chymotrypsin's curve is in pink. Starting with pepsin, its optimal pH is where it displays the greatest amount of activity. We have enzyme activity on the y-axis and the pH on the x-axis. What do you think? The optimal pH for pepsin is right where it displays its optimal activity, corresponding with the x-axis where it has the highest peak. That looks to be about 1.5. Now, if we do the same for chymotrypsin, it's going to be right where it displays its highest amount of activity, corresponding with the x-axis just above 8, so it's about 8. That is the optimal pH of pepsin and the optimal pH of chymotrypsin. Pepsin is typically found in the stomach where the pH is super acidic, about 2. Pepsin is going to be very active in the stomach. Chymotrypsin is found more so in the small intestine where the pH is a little higher, allowing it to operate better in those conditions.

This concludes our lesson on optimal pH, and in our next lesson video, we'll talk about optimal temperatures. I'll see you there.

Optimal Enzyme Conditions

So in addition to having optimal pH, enzymes also have an optimal temperature where they can work at their best and display the temperature in degrees Celsius on the x-axis. Notice that we have these two different curves. We have this green curve here that represents the human enzymes, and then we have this red curve over here that represents the thermophilic bacterial enzymes.

Taking a look at this green curve first, notice that the greatest amount of enzyme activity is showing up right around a temperature of 37 degrees Celsius. It's actually no coincidence that human enzymes have evolved to have an optimal temperature right around 37 degrees Celsius, as the human body temperature is maintained right around 37 degrees Celsius.

Now, if we take a look at this thermophilic bacterial enzyme curve over here, notice that this time, the greatest amount of enzyme activity is showing up at a temperature that's much hotter, right around 77 degrees Celsius. Again, it's no coincidence that the thermophilic bacterial enzymes have evolved to have an optimal temperature that's so hot, right around 77 degrees Celsius. This is because thermophilic bacteria live in very hot environments, such as the hot springs that you can find in Yellowstone National Park, and also the hot hydrothermal vents that can be found on the deep sea ocean floors.

Imagine a scenario where we replace all of the thermophilic bacterial enzymes with human enzymes, but the thermophilic bacteria are still living in their hot environments. In that scenario, all of the human enzymes would denature in those hot environments, and the thermophilic bacteria would die. You can see how the enzymes have evolved to have optimal conditions that reflect the living conditions that they face on a daily basis.

We'll be able to apply these concepts that we've learned about optimal enzyme conditions throughout our course and in our practice problems. So I'll see you guys in our next video.

The best way to increase the reaction rate for an enzyme saturated with substrate is always to:

• A. Increase the pH.
• B. Increase the temperature.
• C. Increase [enzyme].
• D. Increase [substrate].

Which of the following statements about enzymes is false?

• A. Enzymes carry out multiple rounds of a given chemical reaction.
• B. Enzymes accelerate the speed at which reactions get to equilibrium by lowering the activation energy barrier.
• C. Enzymes can denature under highly acidic or basic conditions.
• D. Enzymes push the reaction equilibrium toward product formation.
• E. Enzymes are biological molecular catalysts.

Here’s what students ask on this topic:

What is the optimal pH for pepsin and why?

The optimal pH for pepsin is approximately 1.5. Pepsin is an enzyme found in the stomach, where the environment is highly acidic, with a pH around 2. This acidic environment is necessary for pepsin to maintain its structure and function effectively. The low pH ensures that the ionizable amino acids in the active site of pepsin are in the correct charge state to facilitate enzyme catalysis. If the pH deviates significantly from this optimal value, the enzyme can denature, losing its structure and catalytic ability.

Why do human enzymes have an optimal temperature of 37°C?

Human enzymes have an optimal temperature of 37°C because this is the average body temperature of humans. Enzymes are proteins that catalyze biochemical reactions, and their activity is highly dependent on temperature. At 37°C, human enzymes achieve their highest catalytic efficiency. If the temperature is too low, enzyme activity decreases because molecular movements slow down. If the temperature is too high, enzymes can denature, losing their structure and function. Thus, human enzymes have evolved to work best at the body's natural temperature.

How does pH affect enzyme activity?

pH affects enzyme activity by altering the charges of ionizable amino acids in the enzyme's active site. These charges are crucial for the binding of substrates and the catalytic process. Changes in pH can lead to the protonation or deprotonation of these amino acids, disrupting the enzyme's ability to bind substrates and catalyze reactions. Additionally, extreme pH levels can cause denaturation, where the enzyme loses its three-dimensional structure, rendering it inactive. Each enzyme has an optimal pH at which it functions most efficiently.

What happens to enzymes at temperatures above their optimal range?

At temperatures above their optimal range, enzymes can denature. Denaturation involves the unfolding of the enzyme's three-dimensional structure, which is essential for its catalytic activity. High temperatures cause the weak bonds that maintain the enzyme's structure, such as hydrogen bonds and hydrophobic interactions, to break. This structural change results in the loss of the enzyme's active site configuration, preventing substrate binding and catalysis. Consequently, enzyme activity decreases significantly or stops altogether at temperatures above the optimal range.

Why do thermophilic bacterial enzymes have a higher optimal temperature?

Thermophilic bacterial enzymes have a higher optimal temperature, around 77°C, because these bacteria live in extremely hot environments, such as hot springs and hydrothermal vents. These enzymes have evolved to maintain their structure and function at high temperatures. The amino acid composition and the interactions within these enzymes are adapted to withstand thermal denaturation. This adaptation allows thermophilic bacteria to thrive in conditions that would denature enzymes from organisms living in cooler environments, such as humans.