{"id":321,"date":"2017-10-23T20:05:47","date_gmt":"2017-10-23T20:05:47","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/sunynutrition\/?post_type=chapter&p=321"},"modified":"2017-11-10T18:44:25","modified_gmt":"2017-11-10T18:44:25","slug":"3-43-protein-digestion-in-the-small-intestine","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/suny-herkimer-nutritionflex\/chapter\/3-43-protein-digestion-in-the-small-intestine\/","title":{"raw":"3.43 Protein Digestion in the Small Intestine","rendered":"3.43 Protein Digestion in the Small Intestine"},"content":{"raw":"
\r\n\r\nThe small intestine is the major site of protein digestion by proteases (enzymes that cleave proteins). The pancreas secretes a number of proteases as zymogens into the duodenum where they must be activated before they can cleave peptide bonds1<\/sup>. This activation occurs through an activation cascade. A cascade is a series of reactions in which one step activates the next in a sequence that results in an amplification of the response. An example of a cascade is shown below.\r\n
\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"618\"]\"\" Figure 3.431 An example of a cascade, with one event leading to many more events[\/caption]\r\n\r\n<\/div>\r\nIn this example, A activates B, B activates C, D, and E, C activates F and G, D activates H and I, and E activates K and L. Cascades also help to serve as control points for certain process. In the protease cascade, the activation of B is really important because it starts the cascade.\r\n\r\nThe protease\/colipase activation scheme starts with the enzyme enteropeptidase (secreted from the intestinal brush border) that converts trypsinogen to trypsin. Trypsin can activate all the proteases (including itself) and colipase (involved in fat digestion)1<\/sup> as shown in the 2 figures below.\r\n
\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"615\"]\"\" Figure 3.432 Protease\/colipase activation cascade[\/caption]\r\n\r\n<\/div>\r\n
\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"936\"]\"\" Figure 3.433 The protease\/colipase activation cascade[\/caption]\r\n\r\n<\/div>\r\nThe products of the action of the proteases on proteins are dipeptides, tripeptides, and individual amino acids, as shown below.\r\n
\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"1099\"]\"\" Figure 3.434 Products of pancreatic proteases[\/caption]\r\n\r\n<\/div>\r\nAt the brush border, much like disaccharidases, there are peptidases that cleave some peptides down to amino acids. Not all peptides are cleaved to individual amino acid, because small peptides can be taken up into the enterocyte, thus, the peptides do not need to be completely broken down to individual amino acids. Thus the end products of protein digestion are primarily dipeptides and tripeptides, along with individual amino acids1<\/sup>.\r\n
\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"555\"]\"\" Figure 3.435 Peptidases are produced by the brush border to cleave some peptides into amino acids[\/caption]\r\n\r\n<\/div>\r\nReferences & Links<\/b>\r\n\r\n1. Gropper SS, Smith JL, Groff JL. (2008) Advanced nutrition and human metabolism. Belmont, CA: Wadsworth Publishing.\r\n\r\n<\/div>","rendered":"
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The small intestine is the major site of protein digestion by proteases (enzymes that cleave proteins). The pancreas secretes a number of proteases as zymogens into the duodenum where they must be activated before they can cleave peptide bonds1<\/sup>. This activation occurs through an activation cascade. A cascade is a series of reactions in which one step activates the next in a sequence that results in an amplification of the response. An example of a cascade is shown below.<\/p>\n

\n
\"\"<\/p>\n

Figure 3.431 An example of a cascade, with one event leading to many more events<\/p>\n<\/div>\n<\/div>\n

In this example, A activates B, B activates C, D, and E, C activates F and G, D activates H and I, and E activates K and L. Cascades also help to serve as control points for certain process. In the protease cascade, the activation of B is really important because it starts the cascade.<\/p>\n

The protease\/colipase activation scheme starts with the enzyme enteropeptidase (secreted from the intestinal brush border) that converts trypsinogen to trypsin. Trypsin can activate all the proteases (including itself) and colipase (involved in fat digestion)1<\/sup> as shown in the 2 figures below.<\/p>\n

\n
\"\"<\/p>\n

Figure 3.432 Protease\/colipase activation cascade<\/p>\n<\/div>\n<\/div>\n

\n
\"\"<\/p>\n

Figure 3.433 The protease\/colipase activation cascade<\/p>\n<\/div>\n<\/div>\n

The products of the action of the proteases on proteins are dipeptides, tripeptides, and individual amino acids, as shown below.<\/p>\n

\n
\"\"<\/p>\n

Figure 3.434 Products of pancreatic proteases<\/p>\n<\/div>\n<\/div>\n

At the brush border, much like disaccharidases, there are peptidases that cleave some peptides down to amino acids. Not all peptides are cleaved to individual amino acid, because small peptides can be taken up into the enterocyte, thus, the peptides do not need to be completely broken down to individual amino acids. Thus the end products of protein digestion are primarily dipeptides and tripeptides, along with individual amino acids1<\/sup>.<\/p>\n

\n
\"\"<\/p>\n

Figure 3.435 Peptidases are produced by the brush border to cleave some peptides into amino acids<\/p>\n<\/div>\n<\/div>\n

References & Links<\/b><\/p>\n

1. Gropper SS, Smith JL, Groff JL. (2008) Advanced nutrition and human metabolism. Belmont, CA: Wadsworth Publishing.<\/p>\n<\/div>\n\n\t\t\t

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Candela Citations<\/h3>\n\t\t\t\t\t
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