What happens to proteins during digestion?

Proteins go through several stages during digestion to be broken down into amino acids, the building blocks of proteins. The process of protein digestion involves both mechanical and chemical processes. Here is a summary of what happens to proteins during digestion:

1. Mastication (Chewing):

- Proteins begin to be broken down mechanically by chewing in the mouth. Chewing breaks the proteins into smaller pieces, increasing the surface area for enzymes to work.

2. Gastric Phase:

- Once in the stomach, proteins encounter gastric juices, which contain hydrochloric acid and the enzyme pepsin.

- Hydrochloric acid creates an acidic environment (pH 1-2) that activates pepsin and helps to denature the proteins.

- Pepsin is a protease that begins to break down proteins into smaller polypeptide chains.

3. Small Intestine (Pancreatic Phase):

- As proteins move into the small intestine, the pancreas releases pancreatic juices containing several digestive enzymes, including:

- Trypsin: Breaks down polypeptides into smaller peptides and amino acids.

- Chymotrypsin: Similar to trypsin, it cleaves peptide bonds.

- Elastase: Breaks down the protein elastin, which is found in connective tissue.

- Carboxypeptidases: Remove individual amino acids from the ends of peptide chains.

4. Brush Border Phase (Intestinal Phase):

- The inner lining of the small intestine contains finger-like projections called villi, which have microvilli on their surface.

- Microvilli contain enzymes called peptidases, including aminopeptidases and dipeptidases.

- Peptidases break down smaller peptides into individual amino acids.

5. Absorption:

- The small intestine is responsible for absorbing the majority of the amino acids resulting from protein digestion.

- Amino acids are actively transported across the intestinal epithelial cells into the bloodstream through specific transport proteins.

6. Large Intestine (Colon):

- Any undigested proteins that reach the large intestine are further broken down by bacteria.

- The amino acids produced through bacterial fermentation can be absorbed by the colon.

In summary, proteins are mechanically broken down by chewing and then chemically digested by enzymes in the stomach and small intestine. The end products of protein digestion are amino acids, which are absorbed and used by the body for various functions, including building new proteins and supporting cellular processes.