In this video, we're going to begin our discussion on cofactors. So it turns out that the catalytic activity of many enzymes is actually dependent on the presence of relatively small molecules called cofactors. And so what are cofactors? Well, it turns out that cofactors are just non protein portions of an enzyme, and they are in some way and somehow involved with proper enzyme catalysis. And so that brings us to 2 important terms that you guys need to be familiar with when it comes to cofactors, and the first is an apoenzyme, and the second is a hollow enzyme. And so apoenzymes are enzymes that are inactive, and that's because this is the enzyme without its cofactor. And so because it doesn't have its cofactor, apoenzymes don't work. Now, on the other hand, hollow enzymes are enzymes that are catalytically active, and that's because this is the enzyme with its cofactor. And so this hollow enzyme actually does work. And so down below in our example image, I'll share with you guys something that helps me distinguish between apoenzymes and hollow enzymes. But first, I want you guys to know that cofactors tend to bind to the active sites of enzymes. But the functional roles that cofactors actually have varies greatly from enzyme to enzyme. And we'll be able to talk about that in more depth when we talk about different types of enzyme catalysis later in our course. Now down below in our example image, notice in our central blue box here that this blue dot right dot right here, notice that the enzyme is referred to as an apoenzyme, and the apoenzyme is inactive, meaning it does not work. And, again, that's because it's not bound to its cofactor, which is the red dot. Now when the cofactor binds to the apoenzyme, it becomes a hollow enzyme. And so you can see that the cofactor tends to bind to the active site of the enzyme, which is this, shape, right here. And so the hollow enzyme is actually an active form of the enzyme. And so something that helps me distinguish between apoenzymes and hollow enzymes is that I know that apoenzymes are always trying to apologize. And so here we have a sign and it's saying, I apologize. And the reason that apoenzymes are always trying to apologize is because they are always inactive. They are always saying, I'm inactive right now. And so the reason that they are inactive is again because they are not bound to their cofactor. Now, on the other hand, holoenzymes are enzymes that we know are active. And so if you need an active enzyme, all you need to do is hala at your boy, and your boy is hala enzyme. And so hala enzymes always like, if you need an active enzyme, all you gotta do is hala at me. And so hopefully that'll help you guys remember that holoenzymes are the active version of the enzyme that are bound to the cofactor. And so that concludes our lesson on the introduction to cofactors, and I'll see you guys in our next video.
2
Problem
Problem
Aldoase requires Zn2+ for catalysis. Under cellular conditions of zinc deficiency, aldoase is referred to as:
A
Apoenzyme.
B
Coenzyme.
C
Holoenzyme.
D
Prosthetic group.
3
concept
Cofactor
Video duration:
5m
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Video transcript
So now that we've introduced cofactors, in this video we're going to talk about how cofactors can be broken up into 2 main groups. The first are coenzymes, and the second are metal ions. And so, coenzymes are small organic molecules that are derived from vitamins. And so these include both prosthetic groups and co substrates. And so we've mentioned prosthetic groups in some of our previous lesson videos, and so recall that these are tightly bound, or covalently attached coenzymes, whereas cosubstrates on the other hand are loosely bound and these are recyclable substrate coenzymes. And so really co substrates are very similar to substrates because they are both taken by the enzyme and chemically converted into something different. And so really the main difference between a normal substrate and a co substrate is that co substrates are recyclable, meaning that after they are utilized by an enzyme, they are quickly regenerated back into their normal state. And so examples of cosubstrates include both ATP and NADH. And so we know that ATP can be utilized by an enzyme as a form of energy, and it can be converted into ADP, which has one less phosphate group. And we know from our previous bio courses that there are many processes out there that allow for the regeneration of ATP, converting ADP back into ATP. And so because ATP is recyclable in this fashion and can be quickly regenerated, it's considered a coseubstrate. And for similar logic, NADH is also a coseubstrate. Substrate. So now moving on to our second main group of cofactors, we have the metal ions, and metal ions are pretty much exactly what they sound like. They are metal atoms with a net charge. And just like coenzymes can be further broken up into prosthetic groups and metal ions can be further broken up into metalloenzymes and activator ions. And so metalloenzymes are comparable to prosthetic groups because they are both tightly bound. And so metalloenzymes are enzymes with tightly bound metal ions. Now activator ions are comparable to cosubstrates because they are both loosely bound, and so activator ions are loosely bound metal ions. And it turns out that the, the metalloenzymes tend to be transition metals, such as iron, copper, zinc, and manganese, whereas the activator ions, on the other hand, tend to be alkali and alkali earth metals, such as sodium, potassium, magnesium, and calcium. And so down below, notice that we have these two different charts that are color coded. We have this blue chart, which are all of our coenzymes, and we have the yellow chart, which are our metal ions. And these are certainly not all of the coenzymes that exist, this is just a small portion of relevant coenzymes that we're going to encounter moving forward. But for now, I definitely do not expect you guys to memorize all of these coenzymes and all of these metal ions. I just want to show you guys some examples of coenzymes and metal ions. And so, one thing that I really want you guys to note is that this coenzyme chart on the left has an entire additional column that the metal ion chart does not have, and that is the vitamin precursor. And so that's really important to note that coenzymes are derived from vitamins. And so you can that we have vitamin b 7, b 5, b 2, b 3, and b 6 here, and notice that all of these vitamins also have alternative names. And so that's something important to keep in mind moving forward. Now, again, we're going to talk about each of these enzymes, coenzymes in more detail as we move forward in our course and encounter enzymes that utilize these coenzymes. For instance, we know that biotin is a prosthetic group of an enzyme pyruvate carboxylase, which is very important for gluconeogenesis, which, again, we're gonna talk a lot more about later in our course. And, so essentially what we have are, we have a bunch of prosthetic groups, and really the only, co substrates that are in this list are coenzyme a here and, this right here. These are, the only cosubstrates. The others in the list are co, are prosthetic groups. And so over here on the right, notice we have the, the metal ions, and remember, the metallo ions tend to be transition metals, whereas activator ions tend to be alkali earth and, alkali metals. And so essentially, what you'll notice is that the only metalloenzymes that we have listed here are, the manganese here, and that is it. And so again, moving forward, we're gonna talk a lot more about different coenzymes and metal ions, but this concludes our lesson, and I'll see you guys in our next video.
4
Problem
Problem
Which of the following options is false?
A
Metal ions can bind directly to enzymes or coenzymes.