In this video, we're going to introduce the peptide interbridge. The peptide interbridge is the cross-link between tetrapeptides of adjacent glycan chains. If we take a look at our image down below on the left-hand side, you should notice that this is the structure of peptidoglycan. It consists of these glycan chains, which are repeating NAG and NAM subunits going across here. Here, you can see three glycan chains. Branching off of these glycan chains are these tetrapeptides, which you can see at these positions. These are the tetrapeptides that we talked about in our previous lesson video. What you'll also notice is that in between these tetrapeptides are these interbridges, which you can see here and here and here and here. The gray little circles that you see there are amino acids that serve as the peptide interbridge.
Now, positive cells. Positive cells. They are not going to be found in gram-negative cells. In gram-negative cell walls, the tetrapeptides are going to be linked directly to each other. So, you won’t see peptide interbridges in gram-negative cell walls. You'll only see the peptide interbridges in gram-positive cell walls. This peptide interbridge is going to be important for these gram-positive cells because it helps to form an interconnected network of these peptidoglycan fibers. What you can see here is, once again, these little bridges that I'm highlighting here in blue are the peptide interbridges.
This image over here on the right-hand side is really just a zoom in of this specific region that you see here. When you zoom in, you can see the NAM and NAG repeating subunits. And branching off of the NAM, you have the tetrapeptides. Cross-linking these tetrapeptides is this peptide interbridge. Once again, the peptide interbridge is going to be this region that you see right here. This is going to help to give peptidoglycan a stronger structure and help to link all of these glycan chains together.
This here concludes our brief introduction to the peptide interbridge, and we'll be able to get some practice applying these concepts as we move forward. So I'll see you all in our next video.