Protein digestion refers to the processes by which proteins are broken down into amino acids so that these can be used in the process of protein synthesis. This is an important process that occurs after protein consumption and provides amino acids to the body.
Digestion is mostly carried out via chemical, physical and enzymatic processes that break down proteins into amino acids and/or polypeptides. The main enzymes involved in protein digestion are protease (which cleaves peptide bonds), peptidase (which hydrolyze polypeptides), and nucleases (nucleic acid-specific enzymes).
The chemical digestion of proteins often results in a mixture of free amino acids, with some polypeptides remaining.
A) Protein digestion starts in the stomach and ends in the small intestine
Protein digestion starts in the stomach and ends in the small intestine. The stomach’s acidic environment denatures (unfolds) the protein, making it easier for pepsin to break down the long chains of amino acids into smaller chains.
In the small intestine, pancreatic proteases and intestinal peptidases break down these chains into individual amino acids. These amino acids are absorbed and used by body cells to build new proteins.
Protein digestion begins in the stomach and ends in the small intestine. The major players involved are hydrochloric acid and pepsin, which are produced by the stomach, and trypsin, chymotrypsin, elastase, and carboxypeptidase, which are produced by the pancreas.
Pepsin digests protein into polypeptides and dipeptides. Trypsin, chymotrypsin, elastase, and carboxypeptidase digest polypeptides into amino acids.
B) The majority of protein is broken down into amino acids by the enzymes secreted in salivary gland.
1. The majority of protein is broken down into amino acids by the enzymes secreted in salivary gland.
2. Enzymes that break up proteins are called peptidases or proteases.
3. The majority of protein digestion occurs in the stomach.
4. The enzymes that break down proteins are produced by epithelial cells in the stomach called chief cells or parietal cells and pepsin is one of these enzymes.
5. Pepsin produces peptides, which are short chains of amino acids, but these peptide chains can not be absorbed by the body so they need to be broken down further into their constituent amino acids before they can be absorbed by the small intestine and put to use in the body’s cells and tissues.
6. Protease enzymes from the pancreas called trypsin, chymotrypsin, carboxypeptidase, and elastase convert the peptides into their constituent amino acids that can be absorbed through the wall of the small intestine into the blood stream for delivery to all parts of the body for growth, repair and maintenance of body tissues.
C) When the amino acids leave the stomach and enter the small intestine
When the amino acids leave the stomach and enter the small intestine, the most important part of protein digestion takes place because most amino acids are absorbed into the bloodstream.
The small intestine is more alkaline than the stomach and has digestive enzymes that break down proteins further into amino acids, and other enzymes that absorb these amino acids.
Protein digestion starts in the mouth as salivary amylase breaks down starches. Pepsin also starts to break down proteins in the stomach so that they can be further digested in the small intestine.
Both acidic and alkaline conditions are present during digestion, because each type of enzyme works best at a different pH level.
The process of protein digestion begins in the mouth, where it is broken down by salivary amylase. Enzymes in the stomach, including pepsin, further break down the proteins into smaller chains of amino acids, called polypeptides. They are then absorbed by the stomach.
The intestinal lining has projections that increase its surface area and allow absorption to occur. Protein digestion continues as proteases in the pancreas complete breaking down polypeptides into individual amino acids, which is the smallest form of protein.
Most of these amino acids are absorbed by the small intestine and travel to other body cells for use in building tissue and muscle or for fuel.
D) The enzyme pepsin is activated by hydrochloric acid to break down proteins
The enzyme pepsin is found in the stomach and requires a low pH for optimal activity. Thus, hydrochloric acid is required for protein digestion. Amylase is an enzyme found in the small intestine that breaks down carbohydrates by breaking bonds between the monosaccharides; however, it does not have to be activated by hydrochloric acid.
The pancreas releases enzymes into the duodenum to continue breaking down proteins, fats, and carbohydrates. No hydrochloric acid or activation is required of these enzymes. Finally, bile acids are used by the liver to emulsify fat molecules so that lipase can break them down further.
Conclusion
When digesting protein, there are two parts to the process: proteolysis and peptidolysis. Proteolysis starts in the stomach when cations like Na+ and K+ bind with proteins and other nutrients, essentially denaturing them.
The proteins that are denatured are then broken down by various enzymes including pepsin, trypsin, and chymotrypsin into smaller polypeptide chains that can be used by the body. These polypeptide chains are then passed along to the small intestine where they are further broken down into amino acids.