Digestion and absorption Carbohydrates Dr Jariya Wajahat Biochemistry

Digestion and absorption Carbohydrates Dr Jariya Wajahat Biochemistry of gastrointestinal tract

Whenever Zachariah went into the sanctuary where she was, he found that she had food. He said: O Mary! Whence cometh unto thee this? She answered: it is from Allah gives without stint to whom he will. 37 the family of Imran Al-Qur’an Dr Jariya Wajahat Biochemistry of gastrointestinal tract

Carbohydrates DIET Dr Jariya Wajahat Biochemistry of gastrointestinal tract

Dietary carbohydrates • Largest source of calories – 40 -45% • Plant – starch ( grains, tubers, veggies ) sucrose glucose fructose dietary fiber • Animal – glycogen glycolipids lactose Dr Jariya Wajahat Biochemistry of gastrointestinal tract

Carbohydrates in our diet CH₂OH OH OH OH β-D-glucose Dr Jariya Wajahat OH α-D-glucose Biochemistry of gastrointestinal tract

Carbohydrates in our diet CH₂OH OH OH OH β-D-galactose Dr Jariya Wajahat OH α-D-glucose Biochemistry of gastrointestinal tract

Carbohydrates in our diet CH₂OH HOCH₂ O O OH OH CH₂OH OH OH β-D-fructose Dr Jariya Wajahat OH α-D-glucose Biochemistry of gastrointestinal tract

Carbohydrates in our diet CH₂OH O O OH OH β-D-glucose Dr Jariya Wajahat α-D-glucose Biochemistry of gastrointestinal tract

Carbohydrates in our diet CH₂OH O O OH OH β-D-galactose Dr Jariya Wajahat α-D-glucose Biochemistry of gastrointestinal tract

Carbohydrates in our diet CH₂OH HOCH₂ O O OH CH₂OH OH β-D-fructose Dr Jariya Wajahat OH α-D-glucose Biochemistry of gastrointestinal tract

Carbohydrates in our diet CH₂OH O O OH OH α-D-glucose Dr Jariya Wajahat α-D-glucose Biochemistry of gastrointestinal tract

Carbohydrates in our diet So what’s our relationship? O α-D-glucose O O β-D-fructose Sucrose Dr Jariya Wajahat Biochemistry of gastrointestinal tract Its called α-1— 2 glycosidic bond

Carbohydrates in our diet Its called β-1— 4 glycosidic bond So what’s our relationship? O O Lactose Dr Jariya Wajahat Biochemistry of gastrointestinal tract O

Carbohydrates in our diet Its called α-1— 4 glycosidic bond So what’s our relationship? O O O Maltose Dr Jariya Wajahat Biochemistry of gastrointestinal tract

Carbohydrates in our diet Of course! It’s the α-1— 4 glycosidic linkages So what’s our relationship? O O O Maltotriose Dr Jariya Wajahat Biochemistry of gastrointestinal tract

Carbohydrates in our diet Its called α-1— 6 glycosidic bond So what’s our relationship? O O O Iso- maltose Dr Jariya Wajahat Biochemistry of gastrointestinal tract

Carbohydrates in our diet Its called α-1— 1 glycosidic bond , is’nt it cool? So what’s our relationship? O O O Trehalose Dr Jariya Wajahat Biochemistry of gastrointestinal tract

Carbohydrates in our diet O So what’s our relationship? O Its called β-1— 2 glycosidic bond O Lactulose I don’t understand! O Dr Jariya Wajahat O O Biochemistry of gastrointestinal tract

Carbohydrates in our diet O O O Amylose Dr Jariya Wajahat O Biochemistry of gastrointestinal tract O We’ve got a strong relashionship, the α-1— 4 glycosidic linkage

Carbohydrates in our diet O We are stronger, we have got α-1— 4 glycosidic linkages as well α-1— 6 branch points O O O O Amylo-pectin Dr Jariya Wajahat O Biochemistry of gastrointestinal tract O

Carbohydrates in our diet O O Biochemistry of gastrointestinal tract O O Cellulose Dr Jariya Wajahat O O We are a team, we have got the β-1— 4 glycosidic linkages!

Carbohydrates DIGESTION Dr Jariya Wajahat Biochemistry of gastrointestinal tract

Digestion of carbohydrates • Endoglycosidases / exoglycosidases – specific for sugar, type of bond, number of saccharide units • Glycosidases – Enzymes that hydrolyze glycosidic bonds b/w sugars Dr Jariya Wajahat Biochemistry of gastrointestinal tract

Mouth • Salivary alpha amylase – Endoglycosidase • internal alpha 1, 4 bonds • random intervals – No activity against • Alpha 1, 6 bonds • Little or no activity against Alpha 1, 4 bond at non reducing ends Dr Jariya Wajahat Biochemistry of gastrointestinal tract

O Salivary α-amylase O O O O O Shortened polysaccharides α-limit dextrins Dr Jariya Wajahat Biochemistry of gastrointestinal tract O

Stomach • Salivary alpha amylase – Inactivated by gastric HCl Dr Jariya Wajahat Biochemistry of gastrointestinal tract

Small intestine • • • Pancreatic alpha amylase Bicarbonate Intestinal disaccharidases Dr Jariya Wajahat Biochemistry of gastrointestinal tract

Pancreatic α-amylase • Endoglycosidase – Continues digestion of starch and glycogen • • • Limit dextrins Maltotriose Maltose • Duodenum 4 -9 glycosyl residues and 1 or more 1, 6 branches O O O O Dr Jariya Wajahat Biochemistry of gastrointestinal tract

Intestinal disaccharidases Glucoamylase Sucrase isomaltase complex Lactase glucosylceramidase/ β-glycosidase complex • Trehalase • • • Dr Jariya Wajahat Biochemistry of gastrointestinal tract

Glucoamylase • Really an oligosaccharidase – Hydrolyses 1, 4 bonds of dextrins – Exoglucosidase – Begins at nonreducing end and sequentially cleaves glycosyl units – It cleaves dextrins down to isomaltose O • Highest activity in ileum O O O Dr Jariya Wajahat O O O O Biochemistry of gastrointestinal tract O O

Sucrase-isomaltase complex • Sucrase-maltase – Splits sucrose, maltose and maltotriose • Isomaltase-maltase – Splits alpha 1, 6 bonds in isomaltose and limit dextrins – alpha 1, 4 bonds in maltose and maltotriose • Jejunum Dr Jariya Wajahat Biochemistry of gastrointestinal tract

Sucrase-isomaltase complex O O O Sucrose Dr Jariya Wajahat Biochemistry of gastrointestinal tract

Sucrase-isomaltase complex O O O Maltose Dr Jariya Wajahat Biochemistry of gastrointestinal tract

Sucrase-isomaltase complex O O O Iso- maltose Dr Jariya Wajahat Biochemistry of gastrointestinal tract

Lactase glucosylceramidase/ β-glycosidase complex • Glucosyl Ceramidase – Splits β-glycosidic bonds b/w glucose/galactose and hydrophobic residues • Lactase – Splits β 1, 4 bonds b/w glucose and galactose • Jejunum Dr Jariya Wajahat Biochemistry of gastrointestinal tract

β-glycosidase complex O Dr Jariya Wajahat O Biochemistry of gastrointestinal tract O

Glycolipids • Cerebrosides – Ceramide-monosaccharides GLU CERAMIDE • Globosides – Ceramide-oligosaccharides GLU Dr Jariya Wajahat GAL CERAMIDE Biochemistry of gastrointestinal tract

Glycolipids • Forssman antigen – Ceramide-oligosaccharides GALNAc Dr Jariya Wajahat GALNAc GAL GLU Biochemistry of gastrointestinal tract CERAMIDE

Trehalase • Splits α 1, 1 bond in trehalose • Found in mushrooms, insects and seafood O O O Trehalose Dr Jariya Wajahat Biochemistry of gastrointestinal tract

Carbohydrates ABSORPTION Dr Jariya Wajahat Biochemistry of gastrointestinal tract

Absorption of monosaccharides • • • Glucose Fructose Galactose Hi! O O • Site – Duodenum – Upper jejunum O Dr Jariya Wajahat Biochemistry of gastrointestinal tract

Na+ GLUT 5 O Na+ 2 K+ O 3 Na+ SGLT-1 Na+ O O O GLUT 2 O Na+ Na+ Dr Jariya Wajahat Biochemistry of gastrointestinal tract

Na+ GLUT 2 GLUT 5 O Na+ SGLT-1 Na+ O O O GLUT 2 O Na+ Na+ Dr Jariya Wajahat Biochemistry of gastrointestinal tract

Carbohydrates INDIGESTIBLE Dr Jariya Wajahat Biochemistry of gastrointestinal tract

Indigestible carbohydrates • • Cellulose Hemicelluloses Gums Mucilages Pectin Raffinose Lignin Dr Jariya Wajahat Biochemistry of gastrointestinal tract

Colon • Dietary fibre and nondigested carbohydrates – Bacterial action • Gases – H 2, CO 2, methane • Lactate • Short chain FA – Acetic acid – Propionic acid – Butyric acid Dr Jariya Wajahat Biochemistry of gastrointestinal tract

• What is the cause of excessive flatulence after having a meal containing beans? Dr Jariya Wajahat Biochemistry of gastrointestinal tract

Carbohydrates DISORDERS Dr Jariya Wajahat Biochemistry of gastrointestinal tract

Abnormal degradation of disaccharides • Disorders – Lactose intolerance – Disaccharide intolerance – Isomaltase sucrase deficiency – Defect in absorption of fructose • Symptoms – Osmotic diarrhea – Bacterial fermentation • 2 and 3 carbon compounds • Gases Dr Jariya Wajahat Biochemistry of gastrointestinal tract

Lactose intolerance • Etiology – Deficiency of enzyme lactase • Clinical features – Abdominal cramps – GI bloating – Intermittent diarrhea – 45 min-1 hr after eating dairy products Dr Jariya Wajahat Biochemistry of gastrointestinal tract

Lactose intolerance • Treatment – Reduce consumption of dairy products – Consume • • Green veggies Yogurts Cheese Lactase treated products – Lactase pills Dr Jariya Wajahat Biochemistry of gastrointestinal tract

• Yogurt is a dairy product, why is it recommended in lactose intolerance? Dr Jariya Wajahat Biochemistry of gastrointestinal tract

Disaccharide intolerance • Etiology – Hereditary deficiency – Injured Mucosa • Disease, drugs, malnutrition • Clinical features – Osmotic diarrhea – Abdominal cramps – Flatulence Dr Jariya Wajahat Biochemistry of gastrointestinal tract

Sucrase-isomaltase complex deficiency • intolerance of ingested sucrose Dr Jariya Wajahat Biochemistry of gastrointestinal tract

Defect in absorption of fructose • Clinical features – Gas and distented abdomen after eating fruit, sweets or juices Dr Jariya Wajahat Biochemistry of gastrointestinal tract

Carbohydrate disorders DIAGNOSIS Dr Jariya Wajahat Biochemistry of gastrointestinal tract

Disorders of carbohydrate digestion and absorption • Diagnosis – Oral tolerance tests – H 2 breath test Dr Jariya Wajahat Biochemistry of gastrointestinal tract

Carbohydrate disorders TREATMENT Dr Jariya Wajahat Biochemistry of gastrointestinal tract

Treatment • Avoid foods containing specific disaccharide • Tablets and capsules containing enzymes Dr Jariya Wajahat Biochemistry of gastrointestinal tract