Biochemistry - Winter 2024/1 Tutorial 1 - Digestion and Absorption of Carbohydrates PDF

Biochemistry – Winter 2024/1 Tutorial 1: Digestion and Absorption of Carbohydrates Mohamed M. Naguib, Nihal Moustafa Mansour, PhD PhD Assistant Professor of Assistant Professor of Biochemistry...

Biochemistry – Winter 2024/1 Tutorial 1: Digestion and Absorption of Carbohydrates Mohamed M. Naguib, Nihal Moustafa Mansour, PhD PhD Assistant Professor of Assistant Professor of Biochemistry Biochemistry [email protected] [email protected] Tutorial 1 November 13, 2024  Module Assessment  Mock In-class Quizzes  There are no submission requirements.  Part of the homework will be solved/discussed in the tutorial.  Zero grades for in-class quizzes.  Grading System (Two Final Exams)  First Exam (after 5 Weeks)  50%  Second Exam (after the last Week)  50%  To pass this module, you are expected to achieve a minimum overall pass grade of 40% for the module. 2  Module Topics Week no. Topic W 01 Classification of Carbohydrates Digestion and Absorption of Carbohydrates W 02 Metabolism of Carbohydrates I (Glycolysis & Kreb’s cycle) W 03 Metabolism of Carbohydrates II (Glycogen Metabolism & Gluconeogenesis) Hormonal Control of Blood Glucose W04 Lipid Structure and Classification Lipids Digestion, Absorption & Transportation in Blood W 05 Lipid Metabolism (β-Oxidation of Fatty Acids & Ketone Bodies Metabolism) W 06 Classification of Amino acids & Protein Structure Protein Digestion & Absorption W 07 Enzymes I: Basic Concepts Clinical Enzymology W 08 Enzyme Kinetics II: Factors Affecting Enzyme Activity Water & Electrolyte Balance W 09 Water & Fat-Soluble Vitamins W 10 Nucleic Acids Acid-Base Balance 3  Biochemistry – Definition  Biochemistry is a sub-discipline of both Biology and Chemistry. It can be defined as the Chemistry of Life. Carbohydrates Monosaccharides (Sugars) Living Organism Macromolecules Amino acids Proteins (Polymers) Others Water Fatty acids Lipids (Fats) (Organic acids, Wastes, & Glycerol Non-protein amino acids) Vitamins Minerals and Electrolytes Nucleic Acids (DNA and RNA) Nucleotides Micromolecules 4 Lecture 1 The First Class of Biomolecules Is Carbohydrates 5  Carbohydrates – Sources The Main sources of carbohydrates are either from Plant or Animal. A. Plant Source B. Animal Source In Plants, carbohydrates are formed via photosynthesis process in which Animals use plant carbohydrates in the formation carbon dioxide and water are transformed into glucose that is can be; of their own carbohydrates, such as;  Used in the synthesis of other monosaccharides Such as fructose and  Excess glucose is stored as Glycogen (in liver and galactose. muscles).  Used in the synthesis of disaccharides (2 Monosaccharides) Such as maltose  Glucose and galactose is used to form Lactose (in and sucrose. milk).  Used in the synthesis of cellulose (polymer of glucose) in plant cell walls.  Stored in plant in form of starch (polymer of glucose). 6 Lecture 1  Carbohydrates in Diet: Classification The Major Source of Carbohydrates is Found in Plants Dietary Carbohydrates Polysaccharides Disaccharides Monosaccharides Starch Glycogen Cellulose Maltose Sucrose Lactose Galactose Glucose Fructose Brain Grape Fruit The storage The storage A structural Malt sugar Cane (table) Milk sugar sugar sugar sugar carbohydrates in carbohydrates in carbohydrate that is that consists sugar that that consists plants (inside the animal in liver and involved in the of 2 glucose consists of of Glucose and chloroplasts muscles (animal formation of cell walls molecules. Glucose and Galactose. as starch starch) of plant cells (dietary Fructose. Doesn’t need digestion granules) fibers) 7  Carbohydrates Digestion Digestion Process It is the process by which foods (Carbohydrates, Proteins, Lipids) are broken down into their monomers (Monosaccharides, Amino acids, Fatty acids and Glycerol respectively) to facilitate their absorption. It occurs mainly in Mouth & Duodenum. Dietary Carbohydrates Digestible Non-Digestible - Chief source of Energy (4 C/g). - Non-Calorigenic ** Examples: - They exert various beneficial effects on the body - Starch & Glycogen. such as; promoting normal gut motility, - Sucrose, Lactose & Maltose. Preventing constipation, improves glycemic level control in diabetic patients. ** Examples: - Dietary Fibers (Cellulose). - Pectins & Gums. 8  Digestion: Sites & Enzymes  Digestion of carbohydrates occurs at 3 Sites (Mouth, Duodenum, and Upper jejunum of Small Intestine) with the aid of Digestive Enzymes (Glycosidases), which help to speed up hydrolysis of carbohydrates, namely: 1. Salivary Amylase (secreted by Salivary glands). 2. Pancreatic Amylase (secreted by Pancreas). 3. Intestinal Brush Border Enzymes (special enzymes found in microvilli of the Small Intestine that complete digestion). 9  Digestive Enzymes Action 1. Salivary Amylase Salivary Amylase Starch & Glycogen Dextrin + Maltotriose + Maltose & Isomaltose 2. Pancreatic Amylase Pancreatic Amylase Starch & Glycogen Limit Dextrin + Maltotriose + Maltose & Isomaltose 3. Intestinal Brush Border Enzymes (5 Enzymes) Maltase Maltotriose or Maltose 3 Glucose or 2 Glucose Isomaltase Isomaltose 2 Glucose Lactase Lactose Glucose & Galactose Sucrase Sucrose Glucose & Fructose Dextrinase Dextrin & Limit Dextrin Glucose molecules 10  Digestion: Process & End Products - Digestion starts in Mouth, stops in Stomach, the completed in Duodenum & Upper Jejunum of Small Intestine as Follows. Site Mouth Stomach Duodenum Upper Jejunum Dietary Salivary Amylase Pancreatic Maltase Isomaltase Lactase Sucrase Dextrinase carbohydrates X Amylase No digestion. Starch Dextrin Amylase stops Limit Dextrin Glucose & Maltotriose due to the high Maltotriose 3 Glucose molecules Glycogen Maltose/ acidity (pH Maltose/ 2 Glucose Isomaltose 1.5-2.5). Isomaltose 2 Glucose No Digestion Due to lack of cellulase enzyme in humans Cellulose Cellulose Lactose Glucose & Galactose Glucose & Sucrose Fructose Glucose & Fructose No Digestion As no need for digestion (Monosaccharides) Glucose & Fructose - End products of carbohydrate digestion are Monosaccharides (Glucose, Fructose, & Galactose) and Undigested Cellulose. 11  Carbohydrates Absorption Absorption Process It is the process of taking the products of digestion (monomers) across the gastrointestinal (GI) tract walls and into circulation (blood or lymph). It occurs in Ileum.  By the end of digestion, monosaccharides are readily absorbed through the intestinal mucosal cells into the blood stream. Mechanisms responsible for the absorption of monosaccharides: 1. Active Transport, along with sodium by SGLT1 (sodium glucose transporter) against concentration gradient (i.e. from lower to higher concentration that needs ATP)  e.g. Glucose & Galactose. 2. Facilitated (Passive) Transport, by GLUT5 (Glucose transporter 5) with concentration gradient (i.e. from higher to lower concentration)  e.g. Fructose. Brush border (luminal) Baso-lateral  Brain Storming ! Question: Why Glucose has been added to Oral Rehydration Therapy? The answer lies in the transport mechanism (absorption) of glucose. Cause glucose & sodium share the same transport mechanism (Co-transport); Where this glucose allows the intestine to absorb sodium, which in turn drags water to the intestinal cells and hence to the body. This, in turn, is useful in the treatment of diarrhea. 13  Clinical Significance 1. Disorder of Digestion 2. Disorder of Absorption Lactose Intolerance SGLT Deficiency Cause: Lactase Deficiency Cause: Congenital Deficiency of SGLT (Sodium Glucose Transporter). Clinical Features: Diarrhea due to Osmotic Effect of lactose - Bloating due to Clinical Features: Diarrhea. Fermentation of lactose. Management: Avoid milk intake- Yogurt is added to diet. Figure: Lactose Intolerance 14 THE END