Enzymes. How an enzyme is a catalyst that lowers the activation energy in chemical reactions. Factors that affect enzyme activity, including pH, temperature, and substrate concentration. Structure of an enzyme, including a discussion of an apoenzyme, cofactors and coenzymes, and a holoenzyme. Molecules and mechanisms that increase or decrease enzyme activity, including: competitive inhibitors, noncompetitive (or allosteric) inhibitors, allosteric activators, and feedback inhibition (i.e., negative feedback).
Microbiology, part 18: Metabolism - Enzymes
Full Transcript: Microbiology, part 18: Metabolism - Enzymes
Full Transcript: Microbiology, part 18: Metabolism - Enzymes
Hi. I'm Cathy with Level Up RN. In this video, we will be discussing enzymes, including factors that affect enzyme activity, enzyme structure, and enzyme inhibition. At the end of the video, I'm going to give you guys a quiz to test your understanding of some of the key facts I'll be covering, so definitely stay tuned for that. And if you have our Level Up RN microbiology flashcards, go ahead and pull out your flashcards on enzymes so you can follow along with me, and pay close attention to the bold red text on the back of the cards because those are the things that you are likely to get tested on in your micro class.
Enzymes are catalysts for biochemical reactions in a cell. They lower the activation energy required for a chemical reaction to occur. And the activation energy is the energy required to make or break chemical bonds and to convert reactants into products. So enzymes lower this activation energy, which helps to speed up chemical reactions. And it's important to note that enzymes are not used up in these chemical reactions, so they are reusable.
Enzyme activity is affected by a number of factors. One key factor is pH. So enzymes function best within an optimal pH range. If it is too acidic or too basic, then this can cause denaturing of the enzyme, which means that the three-dimensional structure of the enzyme is affected, which in turn can impair its ability to function. Another key factor is temperature. So in general, increased temperature helps to increase the chemical reaction rate. However, temperatures outside the optimal range can cause denaturing of the enzyme. Lastly, the substrate concentration also affects enzyme activity. So the substrate is the substance that reacts with the enzyme during a chemical reaction. When there is an increased amount of substrate, this will increase enzyme activity up until the saturation point is reached, which is the point at which all the enzymes are too busy to handle any more substrate.
Let's now review the structure of an enzyme. The apoenzyme is the inactive protein portion of the enzyme. In order for it to become activated, it requires binding of a helper molecule. Helper molecules include cofactors and coenzymes. A cofactor is an inorganic ion, whereas coenzymes are organic molecules such as ATP and vitamins. Once the cofactor and/or coenzyme binds to the apoenzyme, a hollow enzyme is formed, which is a whole active enzyme. And then the location on the enzyme where the substrate binds is called the active site.
There are different molecules and mechanisms that can inhibit or promote enzyme activity. A competitive inhibitor is a molecule that is similar to the substrate. It binds to the active site of the enzyme, which blocks the substrate from binding, and this, in turn, decreases enzyme activity. A noncompetitive or allosteric inhibitor binds to the enzyme at a location away from the active site. This is called the allosteric site. And this binding causes the enzyme to undergo a conformational change, which changes the shape of the active site.
So for example, in the illustration shown on the screen, binding of the noncompetitive inhibitor caused the active site to change from a square shape to a circle shape. So now the substrate cannot bind to the active site, which prevents enzyme activity. In addition to allosteric inhibitors, there are allosteric activators. An allosteric activator will bind to the enzyme at the allosteric site, so a site away from the active site. This will cause a conformational change and a change in the shape of the active site such that it will help the substrate bind more effectively at the active site. And this, in turn, will increase enzyme activity.
And then, finally, we have feedback inhibition, which is also called negative feedback. This is basically a way for the cell to scale back production if there is too much product. So with feedback inhibition, if the enzymes are super busy making tons of product to the point where there is too much product, then those end products become allosteric inhibitors. So the allosteric inhibitor will bind to the enzyme at the allosteric site, causing a conformational change, which will ultimately decrease enzyme activity.
All right. It's quiz time, and I have four questions for you. Question number one, what is the inactive protein portion of an enzyme? The answer is, apoenzyme. Question number two, a blank is an inorganic ion that activates an apoenzyme. The answer is, cofactor. Question number three, what do you call the location on an enzyme where the substrate binds? The answer is, the active site. Question number four, a blank inhibitor is a molecule that binds to the enzyme's active site, blocking the substrate from binding. The answer is, competitive.
All right. That's it for this video. I hope it was helpful. Thank you so much for watching.
[BLOOPERS]
In addition to allosteric inhibitors, there are-- sorry. Okay.