Enzyme Binding Factors - Online Tutor, Practice Problems & Exam Prep

Enzymes catalyze reactions by forming an enzyme-substrate complex (ES) at the active site, where the substrate binds specifically. Some enzymes require cofactors, non-protein substances that assist in catalysis, such as metal ions. Cofactors remain unchanged during the reaction, enabling enzymes to catalyze repeatedly. Coenzymes, a type of cofactor, are organic molecules derived from vitamins. They enhance substrate binding, allowing the enzyme to convert substrates into products efficiently, demonstrating the critical role of cofactors in enzymatic activity.

Enzyme-Substrate Complex

In this video, we're going to begin our lesson on enzyme binding factors by introducing the enzyme-substrate complex. When an enzyme interacts with its substrate, the substrate binds to the enzyme specifically at a region called the active site. When the substrate binds to the enzyme at the active site, this ends up forming the enzyme-substrate complex. The enzyme-substrate complex is commonly abbreviated as just ES. So, I'll put ES here. The active site, once again, is defined as a very specific region of an enzyme that binds the substrates. Let's take a look at our image down below to look at how substrate binding forms the enzyme-substrate complex. Notice over here on the far left, we're showing the enzyme in red, and the enzyme is commonly abbreviated with just an e. Notice that in black right here, we're showing you the substrate which is really acting as the reactant for this enzyme-catalyzed reaction, and substrates are commonly abbreviated with just the letter s. Notice that the substrate here is going to bind to the active site of the enzyme, which is just this region that we see right here. This other region over here is not the active site. The active site is just a specific region on the enzyme that binds the substrate. Once the enzyme is bound to the substrate, it ends up forming the enzyme-substrate complex. Here in the middle, we can see the substrate is bound to the enzyme, and they are making this fit together. The enzyme-substrate complex is commonly abbreviated as just ES complex. Now after enzyme catalysis, the products are going to be released from the active site, and the enzyme will remain unchanged in the reaction. Notice that after enzyme catalysis, represented by this arrow right here, the substrate in black is being converted into the product over here, which is in green, and the products are commonly abbreviated with just a p. Notice that the enzyme is actually unaltered; it remains unchanged by the end of the reaction. The enzyme still takes on the original form that it had before the reaction took place. This is what we mean by the enzyme being unchanged. Because the enzyme is unchanged, it means it can continuously catalyze this reaction over and over again to continuously make more and more products over time. This concludes our introduction to the enzyme-substrate complex. As we move forward, we'll be able to talk about some more enzyme binding factors. So, I'll see you all in our next video.

Cofactors

In this video, we're going to introduce cofactors, and some enzymes require what are known as cofactors, which are non-protein substances required by an enzyme for catalysis to occur. If there is no cofactor, in some cases, no enzyme catalysis can take place. You can think of cofactors as basically little enzyme helpers. They help the enzyme perform catalysis. Not all enzymes have cofactors, but some do. An example of cofactors includes metal ions. Some enzymes will not be able to perform catalysis without metal ions, which are non-protein because they are not made up of amino acids like proteins. Instead, they are just metal ions. Cofactors are not consumed in the reaction, which means that at the beginning and by the end of the reaction, the cofactor remains the same. Cofactors can assist with enzyme catalysis in many different ways, and we will see an example below in our image.

A coenzyme sounds a lot like a cofactor, and that's because it is a specific type of cofactor. A coenzyme is an organic molecule cofactor. If the cofactor is an organic molecule, containing carbon and hydrogen atoms, then we refer to it as a coenzyme. Not all cofactors are coenzymes because not all cofactors are organic molecules. For example, metal ions are made up of metal atoms and do not contain carbon and hydrogen atoms. It's only the cofactors that are organic molecules that we call coenzymes. Coenzymes tend to be derived from vitamins.

Let's take a look at our example to get a better understanding of how cofactors can assist enzymes with catalysis. Some cofactors can assist in substrate binding. In the image on the left-hand side, notice that the enzyme is shown in red and the substrate in black. Notice that the enzyme's active site here is not ideally tailored for this substrate, so perhaps the substrate could not bind to the active site in some scenarios, and if that happens, the enzyme will not be able to perform catalysis. However, if a cofactor is present, such as the orange structure representing the cofactor, then the cofactor can bind to the active site. Notice here, the cofactor is bound to the active site, which could make the site better suited and better tailored for the substrate. Only in the presence of the cofactor will the substrate be able to bind to the active site. Once the substrate has bound to the active site, as shown on the far right, enzyme catalysis can proceed, and the enzyme can convert the substrate into the product, which is not shown here, but you can imagine the reaction continuing as normal.

This concludes our introduction to cofactors and how they are non-protein substances that are required to help enzymes perform catalysis. We'll get some practice applying these concepts as we move forward in our course, so I'll see you all in our next video.

The organic non-protein components that aid in enzyme catalysis are called:

a) Reactants.

b) Cofactors.

c) Coenzymes.

d) Substrates.

e) Products.

• A. Reactants.
• B. Cofactors.
• C. Coenzymes.
• D. Substrates.
• E. Products.

Here’s what students ask on this topic:

What is the enzyme-substrate complex and how does it form?

The enzyme-substrate complex (ES) forms when a substrate binds to an enzyme at a specific region called the active site. The active site is tailored to fit the substrate, allowing the enzyme to catalyze the reaction efficiently. When the substrate binds to the active site, it forms the ES complex, which facilitates the conversion of the substrate into products. After the reaction, the products are released, and the enzyme remains unchanged, ready to catalyze another reaction. This process is crucial for the enzyme's ability to repeatedly catalyze reactions.

What are cofactors and why are they important for enzyme activity?

Cofactors are non-protein substances required by some enzymes for catalysis. They can be metal ions or organic molecules (coenzymes). Cofactors assist enzymes in various ways, such as enhancing substrate binding or stabilizing the enzyme-substrate complex. Without the necessary cofactors, certain enzymes cannot perform catalysis. Cofactors remain unchanged during the reaction, allowing them to assist the enzyme repeatedly. Coenzymes, a type of cofactor, are often derived from vitamins and play a critical role in ensuring efficient enzymatic activity.

How do coenzymes differ from cofactors?

Coenzymes are a specific type of cofactor that are organic molecules, meaning they contain carbon and hydrogen atoms. In contrast, cofactors can be either organic or inorganic substances. For example, metal ions are inorganic cofactors. Coenzymes are typically derived from vitamins and assist enzymes in catalysis by enhancing substrate binding or stabilizing the enzyme-substrate complex. While all coenzymes are cofactors, not all cofactors are coenzymes.

How do cofactors assist in substrate binding?

Cofactors can assist in substrate binding by altering the active site of the enzyme to better fit the substrate. For instance, a metal ion cofactor might bind to the active site, changing its shape to make it more suitable for the substrate. This enhanced fit allows the substrate to bind more effectively, facilitating the formation of the enzyme-substrate complex and enabling the enzyme to catalyze the reaction efficiently. Without the cofactor, the substrate might not bind as well, hindering the enzyme's catalytic activity.

Why do some enzymes require metal ions as cofactors?

Some enzymes require metal ions as cofactors because these ions can stabilize the enzyme-substrate complex, enhance substrate binding, or participate directly in the catalytic process. Metal ions can help in the proper orientation of the substrate, stabilize charged reaction intermediates, or even participate in redox reactions. Without these metal ions, the enzyme might not achieve the correct conformation or reactivity needed for efficient catalysis, thereby hindering the overall reaction process.