Stomach, protein digestion

The first major food breakdown takes place in the stomach. Protein digestion is the result of the action of secretions from the stomach—an expanded pouch of the gastrointestinal tract located between the esophagus and the duodenum—the intestine, and the pancreas. 

Pepsinogen is produced by the chief cells. Within the lumen of the stomach, this precursor molecule is split by HCl to form the active enzyme pepsin. Optimally active at an acidic pH (pH = 2), pepsin begins protein digestion by fragmenting proteins into smaller peptide chains. 

Amides undergo an acid- or base-catalyzed hydrolysis reaction with water in the same way that esters do. Just as an ester yields a carboxylic acid and an alcohol, an amide yields a carboxylic acid and an amine (or ammonia). The net effect is a substitution of -N by -OH. This hydrolysis of amides is the key process that occurs in the stomach during digestion of proteins. 

Protein digestion starts in the mouth and continues in your stomach and small intestines. This is due to pepsin, which is secreted in the saliva and obviously the gastric juice, followed by pancreatic enzymes, then absorbed by the mucosal cells in the small intestines. In short, the digestive system breaks down protein into its peptide amino acid structures so they can be absorbed in the small intestine via the... 

Dietary proteins, with very few exceptions, are not absorbed rather they must be digested into amino acids, or di- and tripeptides. Protein digestion begins in the stomach, where proenzyme pepsinogen is autocatalytically converted to pepsin A. Most proteolysis takes place in the duodenum via enzymes secreted by the pancreas, including trypsinogen, chymotrypsinogen and pro-carboxypeptidase A. These serine and zinc proteases are produced in the form of their respective proenzymes they are both endopeptidase and exopeptidase, and their combined action leads to the production of amino acids, dipeptides and tripeptides. 

The hydrochloric acid and protein-digesting enzymes of the stomach kill many pathogens. 

Protein digestion begins in the stomach, where the acidic environment favors protein denaturation. Denatured proteins are more accessible as substrates for proteolysis than are native proteins. The primary proteolytic enzyme of the stomach is pepsin, a nonspecific protease that, remarkably, is maximally active at pH 2. Thus, pepsin can be active in the highly acidic environment of the stomach, even though other proteins undergo denaturation there. 

Protein digestion is initiated in the stomach by the action of pepsin in a highly acid medium. The acidity also denatures the protein, unfolding the polypeptide chains for better access by the gastric, pancreatic, and intestinal proteolytic enzymes. Additionally, the polypeptides and amino acids... 

The small intestinal tract is the major place of digestion and absorption. Protein digestion reaches approximately 15% in the stomach, and in the lower intestine, the hydrolyzed fraction amounts to about 60%. Seventy percent of fats, 60% of carbohydrates, and about 30% of protein and peptide are absorbed within the duodenum. Within enterocytes, triglycerides are resynthesized from long-chain fatty acids and transformed into chylomicrons, which are transported via the lymphatic system, whereas short- and medium-chain fatty acids are directly transported into mesenteric and portal vein system. 

Protein digestion begins in the stomach, where protein is denatured by the low pH and is exposed to the action of pepsin. The low pH also provides the optimal H+ concentration for pepsin activity. The zymogen precursor pepsinogen (M.W. 40,000) is secreted by the chief cells and is converted to pepsin (M.W. 32,7(K)) in the acid medium by removal of a peptide consisting of 44 amino acid residues. This endopeptidase hydrolyzes peptide bonds that involve the carboxyl group of aromatic amino acid residues, leucine, methionine, and acidic residues (Table 12-5). The products consist of a mixture of oligopeptides. 

In the stomach food is stored while further digestion takes place. The stomach produces acid and enzymes to begin protein digestion. It can take 2-4 hours before food is passed onto the small intestine. 

Some of the basics have been known for some time. Since the function of gastric secretions is to initiate protein digestion, the wall of the stomach itself must be protected from this destructive process. To a large extent this was believed to be accomplished by abundant secretion of mucous by mucous-producing cells as well as the gastric glands, which also secrete the gastric juice. It is not likely that all the cytoprotective mechanisms have been identified. 

Essential amino acids must be acquired in the diet nonessential amino acids can be synthesized by the body. Complete proteins contain all the essential and nonessential amino acids. Incomplete proteins are missing one or more essential amino acids. Protein digestion begins in the stomach, where proteins are degraded by the enzyme pepsin. Further digestion occurs in the small intestine by enzymes such as trypsin and chymotrypsin. 

The digestion of proteins begins in the stomach, where the low pH denatures the proteins so that they are more easily hydrolyzed by the enz)une pepsin. They are further degraded in the small intestine by tiypsin, ch)miotiypsin, elastase, and other proteases. The products of protein digestion—amino acids and short oligopeptides—are taken up by the cells lining the intestine. This uptake also involves an active transport mechanism. 

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