Models of Enzyme Action - Online Tutor, Practice Problems & Exam Prep

Enzymes interact with substrates through two primary models: the lock and key model and the induced fit model. In the lock and key model, the active site is rigid and matches the substrate precisely, akin to a key fitting into a lock. Conversely, the induced fit model suggests that the active site is flexible, changing shape to accommodate the substrate, which is more representative of actual enzyme behavior. Understanding these models is crucial for grasping enzyme specificity and the activation energy (E_act) required for biochemical reactions.

Models of Enzyme Action Concept 1

Now, we know that the substrate interacts with the active site of the enzyme. And with this idea, we need to understand that there are two models of enzyme action. Now, here we're going to say the two models that describe how enzymes interact with substrates are our lock and key model, and then our induced fit model. So if we take a look at the lock and key model, we're going to say here the active site is rigid and unchanging. And we're going to say here for this type of model, the substrate fits in like a key into a lock. And we know that a key is very specific for the type of lock that it goes into. The same thing here when it comes to enzyme and substrate interactions. Here we're going to say that the active site is identical in shape to the substrate. So here, when we take a look at this example, we have our substrate, and then we have the active site of the enzyme. The substrate is approaching it. The substrate matches the grooves, the overall shape of the active site of the enzyme perfectly, so that when it comes in, it locks in exactly as it's supposed to.

Now, the induced fit model is another way of looking at what could happen between an enzyme and a substrate. Here, we're going to say that in the induced fit, the active site is flexible and changes. And we're going to say that it changes shape to accommodate the substrate. We're going to say the active site resembles the substrate. It's not an identical match to the substrate it just resembles it; it's in the ballpark. And we're going to say this is a more accurate model of enzyme action. We don't typically get a lock and key model when it comes to enzyme and substrate interactions. They don't match up perfectly. What happens here is we have our enzyme, and here we have our substrate. We can see that the grooves of the active site of the enzyme don't match up perfectly with the grooves of this substrate. But it's okay because the substrate comes in and goes into the active site of the enzyme, and the enzyme changes shape to accommodate this incoming substrate. So here, we're going to say we're going to have a change in shape of the active site. And in this way, we are still able to obtain our complex, our enzyme-substrate complex. So just remember, these are the two different models in which an enzyme and a substrate can interact with one another.

Models of Enzyme Action Example 1

Which correctly describes the lock and key model?

• A. Enzyme undergoes a change in shape to accommodate the substrate at the active site. No. In a lock and key model, the substrate and the active site of the enzyme need to be identical in terms of shape, so this wouldn't happen.
• Next, the enzyme irreversibly binds to the substrate to form products. Now here it doesn't matter which of the two models we follow, this is not going to happen. It can't be irreversibly binding. Remember, it needs to be a non-covalent bond between the substrate and the active site of the enzyme. In that way, the substrate can attach, get transformed into products, and then be released from the enzyme.
• C. Active site of enzyme has a fixed shape that perfectly matches the shape of the substrate. This is true. This is the lock and key model.
• D. The enzyme is able to interact with many different substrates. Now, here in lock and key model, the active site and the substrate need to be perfect. They need to be identical to one another. This greatly limits the types of substrates and the variety of substrates that can attach, so this would not be true. You wouldn't be able to get many different substrates attaching. You need a more flexible shape in terms of the active site, which is not the lock and key model.

So here, option C would be our only answer.

Match each model with correct descriptions: (a) Induced fit model, (b) Lock and key model.

________ Active site undergoes changes in shape during reaction.

________ Enzyme is specific only to one substrate.

________ Shape of active site is similar to that of substrate. 

________ Enzyme model that more accurately describes substrate-enzyme interactions.

For this practice question, it says, match each model with correct descriptions. So, for a, we're going to have the induced fit model, and for b, we're going to have the lock and key model. So, for the first statement, it says, the active site undergoes changes in shape during the reaction. This perfectly describes the induced fit model, where the active site of the enzyme and the substrate don't perfectly match. They just resemble one another. And there's going to be a change in the shape of the active site in order to accommodate the substrate. So this would be a. Enzyme is specific only to 1 substrate. This is our lock and key model. The active site of the enzyme and the substrate shape have to be identical. There is no wiggle room, no shape change, none of that. They fit perfectly with one another. Shape of an active site is similar to that of the substrate. This again would be our induced fit model. The active site of the enzyme and the shape of the substrate are not identical; they just resemble one another. Yet, it's close enough in terms of shapes that they can accommodate one another once they bind together. Then finally, the enzyme model that more accurately describes substrate enzyme interactions. Yes. We have to be able to use different types of substrates for an active site of an enzyme, so it's best to follow the induced fit model where they just resemble one another and the enzyme itself can transform in order to better accommodate different types of substrates. So this would be our induced fit model as well. So this is how we describe each one of these four statements within this practice question.

Here’s what students ask on this topic:

What is the lock and key model of enzyme action?

The lock and key model of enzyme action suggests that the active site of an enzyme is rigid and unchanging, fitting the substrate precisely like a key fits into a lock. In this model, the active site is identical in shape to the substrate, ensuring a perfect match. This specificity means that only the correct substrate can bind to the enzyme, forming an enzyme-substrate complex. This model emphasizes the high specificity of enzyme-substrate interactions, but it is less representative of actual enzyme behavior compared to the induced fit model.

How does the induced fit model differ from the lock and key model?

The induced fit model differs from the lock and key model in that the active site of the enzyme is flexible and changes shape to accommodate the substrate. Unlike the lock and key model, where the active site is rigid and matches the substrate precisely, the induced fit model suggests that the active site only resembles the substrate. When the substrate approaches, the enzyme undergoes a conformational change to fit the substrate more snugly. This model is considered more accurate as it reflects the dynamic nature of enzyme-substrate interactions in biological systems.

Why is the induced fit model considered more accurate than the lock and key model?

The induced fit model is considered more accurate than the lock and key model because it better represents the dynamic nature of enzyme-substrate interactions. In the induced fit model, the active site of the enzyme is flexible and changes shape to accommodate the substrate, reflecting the actual behavior of enzymes in biological systems. This flexibility allows for a broader range of substrates to be accommodated and explains how enzymes can achieve high specificity and catalytic efficiency. The lock and key model, with its rigid active site, does not account for the conformational changes that enzymes typically undergo during substrate binding.

What are the two primary models of enzyme action?

The two primary models of enzyme action are the lock and key model and the induced fit model. The lock and key model suggests that the active site of the enzyme is rigid and matches the substrate precisely, like a key fitting into a lock. In contrast, the induced fit model proposes that the active site is flexible and changes shape to accommodate the substrate, making it a more accurate representation of enzyme behavior. Understanding these models is crucial for grasping enzyme specificity and the activation energy required for biochemical reactions.

How do enzymes achieve specificity in their interactions with substrates?

Enzymes achieve specificity in their interactions with substrates through the precise fit between the enzyme's active site and the substrate. In the lock and key model, this specificity is due to the rigid and unchanging nature of the active site, which matches the substrate exactly. In the induced fit model, the active site is flexible and undergoes conformational changes to fit the substrate more snugly. This adaptability allows enzymes to bind specifically to their substrates, ensuring that only the correct substrate can form an enzyme-substrate complex, thereby facilitating the biochemical reaction.