Which of the following statements is incorrect about the digestion of proteins?
- A. Denaturation in the stomach makes the peptide bonds accessible to proteases. That's true; remember that we're going to have the denaturation of our protein within the stomach. This has to occur so that later on the proteases can start to hydrolyze those proteins into amino acids. So, this is true.
- B. Pepsin in the stomach breaks large proteins into smaller polypeptides. Yes, that is true. Pepsin is going to be the enzyme that we find within our stomach, and it's going to break down our larger proteins into polypeptides.
- C. Proteases in the small intestines hydrolyze proteins and polypeptides into free amino acids. That is also true.
- D. Here, protein digestion begins in the mouth by enzymes in the saliva. Remember, your saliva doesn't have enzymes that are going to help with the breaking down of our macromolecules. So this part is false. So, out of all the options, the answer has to be option D. Yes, mechanical digestion can begin in the mouth, but saliva doesn't have the necessary enzymes to start breaking down and denaturing our proteins. That's going to happen later on within the stomach.