Protein Digestion Process Overview
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Questions and Answers

Where does protein digestion begin?

  • Esophagus
  • Large intestine
  • Stomach (correct)
  • Small intestine

What activates pepsinogens to become pepsins in the gastrointestinal tract?

  • Intestinal bacteria
  • Pancreatic enzymes
  • Saliva
  • Gastric acid (correct)

In what form are pepsins secreted in the stomach?

  • Fats
  • Inactive precursors (correct)
  • Fully activated enzymes
  • Proteins

Which type of pepsinogen is found only in acid-secreting regions?

<p>Pepsinogen I (D)</p> Signup and view all the answers

What does maximal acid secretion correlate with in the context of pepsinogens?

<p>Pepsinogen I levels (D)</p> Signup and view all the answers

What is the pH optimum range for pepsins during protein digestion?

<p>1.6–3.2 (B)</p> Signup and view all the answers

Where does the action of pepsins get terminated during protein digestion?

<p>Duodenum (A)</p> Signup and view all the answers

What kind of bonds do pepsins hydrolyze during protein digestion?

<p>Bonds between aromatic amino acids and a second amino acid (C)</p> Signup and view all the answers

Which enzyme acts at interior peptide bonds in peptide molecules during small intestine digestion?

<p>Trypsin (C)</p> Signup and view all the answers

Where is pepsinogen I predominantly found in the stomach?

<p>Acid-secreting regions (A)</p> Signup and view all the answers

Study Notes

Protein Digestion

  • Protein digestion begins in the stomach, where pepsins cleave some of the peptide linkages.
  • Pepsins are secreted in the form of inactive precursors (proenzymes) and activated in the gastrointestinal tract.
  • The pepsin precursors are called pepsinogens and are activated by gastric acid.

Pepsinogens

  • Human gastric mucosa contains a number of related pepsinogens, which can be divided into two immunohistochemically distinct groups: pepsinogen I and pepsinogen II.
  • Pepsinogen I is found only in acid-secreting regions, whereas pepsinogen II is also found in the pyloric region.
  • Maximal acid secretion correlates with pepsinogen I levels.

Action of Pepsins

  • Pepsins hydrolyze the bonds between aromatic amino acids (such as phenylalanine or tyrosine) and a second amino acid.
  • The products of peptic digestion are polypeptides of very diverse sizes.
  • Pepsins have a pH optimum of 1.6–3.2, and their action is terminated when the gastric contents are mixed with the alkaline pancreatic juice in the duodenum and jejunum.

Pancreatic and Intestinal Digestion

  • In the small intestine, the polypeptides formed by digestion in the stomach are further digested by the powerful proteolytic enzymes of the pancreas and intestinal mucosa.
  • Trypsin, the chymotrypsins, and elastase act at interior peptide bonds in the peptide molecules and are called endopeptidases.
  • The pH of the intestinal contents in the duodenal bulb is 3.0–4.0, but rapidly rises; in the rest of the duodenum it is about 6.5.

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Description

Learn about the process of protein digestion, starting in the stomach where pepsins cleave peptide linkages, and how pepsinogens are activated by gastric acid. Explore the key steps involved in breaking down proteins in the gastrointestinal tract.

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