Lecture 07 - Carbohydrates

Lecture 07 - Carbohydrates - Lecture 07 - Carbohydrates...

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Lecture 07 - Carbohydrates Carbohydrate assimilation ( principles of digestion ) The intestine can only transport monosaccharides (single units) Dietary polymers and disaccharides must be digested i.e. table sugar = disaccharides Digestion occurs in two phases Luminal digestion Carbohydrate is in the lumen of the gut and acted on the many enzymes (saliva, pancreas, and stomach (enzyme are present in the intestinal contents and begin the digestion process) Brush-border digestion via membrane-bound hydrolases The surface of the GI epithelium w/ microvilli Enzyme in this second phase are on the microvilli and they perform the final step of digestion Carbohydrate assimilation (general features) Major source of calories in the human diet Three major nutritional forms Starch Sucrose (disaccharides) Lactose (disaccharides found in milk) The proportion of calories obtained from each varies in different populations Carbohydrate assimilation ( starch ) A mixture of large glucose polymers Amylose – straight chain polymers; 100 of glucose bound together– 25% Amylopectin – complex, branched polymers of glucose; add to structure integrity – 75% Multiple dietary sources Cereal products Breads Starchy vegetables (potato) Carbohydrate assimilation ( Dietary fiber ) A number of other carbohydrate polymers cannot be digested by either pancreatic or intestinal carbohydrases Together with related non-carbohydrate polymers, these make up dietary fiber Can be hydrolyzed to varying extents by colonic bacteria Important source of short chain fatty acids produced by the bacteria Carbohydrate assimilation ( Amylase ) Two related isoforms Salivary – likely important in pancreatic insufficiency and infants The salivary enzyme is like a backup if the pancreatic isn’t secreted Important when pancreatic is insufficient! Pancreatic Doing the bulk of the work enzyme is very acid sensitive Inactivated by acidic pH (especially salivary) but active site can be protected in the presence of substrate (acid will inactivate only when substrate is not there) Synthesis and secretion regulated by neurohumoral input , related to food ingestion Closely coordinated with the food ingestion! Carbohydrate assimilation (
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This note was uploaded on 09/14/2011 for the course PHARM gs taught by Professor Staff during the Spring '11 term at UCSD.

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Lecture 07 - Carbohydrates - Lecture 07 - Carbohydrates...

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