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Question Video: Describing the Role of Pepsin in Gastric Digestion Biology

What is the main function of pepsin in gastric digestion?


Video Transcript

What is the main function of pepsin in gastric digestion? (A) To break down polysaccharides into small sugars. (B) To emulsify fats. (C) To break down proteins into smaller fragments of polypeptides. Or (D) to initiate peristalsis in the esophagus.

To correctly determine the function of pepsin, let’s start by reviewing a key term we are given. You may remember that gastric digestion refers to mechanical and chemical digestive processes that occur in the stomach. It is one of the three major categories based on the location of digestion, with the other two being buccal, the mouth, and intestinal, the small intestines.

Because we can’t voluntarily contract them, it’s easy to forget that the stomach wall has three layers of smooth muscle tissue. However, these muscles are capable of involuntary contractions. In fact, it is the rhythmic contraction and relaxation of these smooth muscles, called peristalsis, that is responsible for mechanical gastric digestion.

Chemical gastric digestion begins when food mixes with stomach acid, also called gastric juice. Gastric juice is a strong acid, and the low pH environment it creates stimulates a substance called pepsinogen to be converted to its active enzymatic form. Pause the video and see if you can figure out which enzyme pepsinogen is converted to. If you said pepsin, you are correct.

Pepsin is a type of protease, which is an enzyme that catalyzes the hydrolysis of proteins into smaller subunits. Pepsin breaks down proteins into shorter polypeptide chains that will be further broken down in the small intestine into single amino acids. Now that we understand the function of pepsin, let’s return to our answer choices.

Polysaccharides are broken down into smaller sugars by enzymes called carbohydrases. This occurs during buccal and intestinal digestion, not during gastric digestion. So we can eliminate choice (A). Fats are emulsified by bile, a substance released by the liver. So we can rule out choice (B) as well. Finally, we can rule out answer choice (D), because although food travels through the esophagus to reach the stomach, the esophagus is not part of gastric digestion.

Therefore, the correct answer to our question is (C). The function of pepsin in gastric digestion is to break down proteins into smaller fragments of polypeptides.

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