Protein Digestion and Absorption

Question

9 of 28
Chyme travels from the stomach to the small intestine.
Enzymes from the pancreas are secreted
Into the smalli
Intestine.
Hydrochloric acid denatures proteins and activates pepsinogen to form pepsin.
Pepsin breaks down proteins into polypeptide strands.
A bolus enters
ine stomach.
Enzymes in the small intestine break down polypeptide strands into mostly tripeptides and dipeptides.
Tripeptides and dipeptides are broken down into single amino acids that enter the blood
and travel to the liver.
Mechanical digestion
in the mouth breaks down the food
Take a bite of a peanut butter sandwich
Amino acids enter the circulatory system.

Answer 1

The process of protein digestion and absorption involves several steps and organs in the digestive system. Here's a brief overview of each stage, following the points you've provided:

1. Ingestion: When you take a bite of a peanut butter sandwich, the mechanical digestion begins in the mouth. Chewing breaks down the food into smaller pieces, increasing the surface area for enzymes to act upon. Saliva, which contains the enzyme amylase, starts the digestion of carbohydrates, but protein digestion will primarily occur later.

2. Swallowing: The chewed food, now called a bolus, is swallowed and travels down the esophagus to the stomach.

3. Stomach: In the stomach, hydrochloric acid (HCl) plays a crucial role. It denatures the protein structures, unraveling them and making them more accessible to enzymes. HCl also activates pepsinogen, an inactive precursor, to pepsin, an active enzyme that begins protein digestion by breaking down proteins into smaller polypeptide strands.

4. Chyme Formation: As the stomach churns, the food mixes with gastric juices, forming a semi-liquid substance known as chyme.

5. Small Intestine: Chyme is then released into the small intestine. Here, pancreatic enzymes (like trypsin and chymotrypsin) further break down the polypeptide strands into smaller peptides, mostly resulting in tripeptides and dipeptides.

6. Brush Border Enzymes: In the small intestine, the brush border of the intestinal lining contains enzymes that complete the digestion of peptides. These enzymes break down tripeptides and dipeptides into single amino acids.

7. Absorption: The single amino acids are then absorbed through the intestinal walls into the bloodstream. This absorption occurs via specific transport systems that facilitate the uptake of amino acids against their concentration gradient.

8. Circulation: Once absorbed, the amino acids enter the circulatory system and are transported to the liver, where they may be utilized for various functions, including protein synthesis and production of other nitrogen-containing compounds.

Overall, the digestion of proteins is a complex process that requires both mechanical and chemical actions, involving various organs and enzymes working together to break down dietary proteins into absorbable units—single amino acids.