In this video, we're going to briefly talk about the significance of protein breakdown as we review the peptidase chymotrypsin. Protein breakdown is actually critical to living systems for many different reasons, including the following two reasons. The first is that proteins and enzymes that are no longer needed inside of the cell can be degraded through protein breakdown so that their amino acids can be recycled and used to build other proteins and enzymes that are needed. Now the second reason for why protein breakdown is so critical to living systems is that proteins that are ingested through the diet actually need to be broken down in order to be absorbed by our intestines and used by our cells.
Recall from our previous lesson videos that peptidases are just the specific class of enzyme that catalyzes protein breakdown. And of course, this specific enzyme, chymotrypsin, is an example of a peptidase. It is a digestive hydrolase enzyme that breaks down proteins. Recall from our previous lesson videos that chymotrypsin actually has a preference for which amino acid residues it recognizes for cleavage. It always cleaves at the C-terminal end, and it typically has a preference for these aromatic amino acid residues which are Phenylalanine, Tyrosine, and Tryptophan. It also has a lower preference for Leucine and Methionine. However, moving forward, we're mainly going to be focusing on the aromatic amino acid residue preference for chymotrypsin.
As we'll see down below, chymotrypsin is going to be secreted by the pancreas in response to eating a meal. If we take a look at our example image over here on the left, notice we have this human figure who, if we zoom in on his digestive system right here, we can see that we have his stomach right here. Inside of his stomach, we've got some broccoli for those of you who are vegetarians out there, and broccoli is a vegetable that is quite high in protein. As this broccoli makes its way through the digestive system, you'll notice that we have an organ here called the pancreas that's responsible for ultimately secreting chymotrypsin.
Recall that chymotrypsin actually has a zymogen, that's referred to as chymotrypsinogen. Originally, the cells of the pancreas will secrete chymotrypsinogen in its zymogen form, which is the inactive form, and then chymotrypsinogen through cleavage here, which is why we have the scissors, can be activated into chymotrypsin, and then chymotrypsin can finally begin to degrade the proteins of the broccoli that we ingested through eating a meal. Notice, over here on the right, we're showing you a specific peptide right here. Notice that we're showing you that there are specific cleavage points here when we treat this peptide with chymotrypsin. And so recall that it recognizes aromatic amino acid residues. Notice right here in the blue background we have Phenylalanine that's being recognized. And of course, the C-terminal end is what gets cleaved. So over here, we have the C-terminal end. And so that's why this peptide bond is being cleaved. Then we also have Tyrosine here, and Tyrosine is another aromatic amino acid residue. The C-terminal peptide bond also gets cleaved. So on the left, what we have is just one peptide fragment, but after the two cleavages, we end up getting three separate peptide fragments that are color-coded here. We get this blue fragment right here. This green fragment here, and then we have the purpleremainder and a review of chymotrypsin's activity. In our next video, we'll be able to talk specifically about chymotrypsin's active site. So I'll see you guys in that video.
