Post on 30-Mar-2015
Dr Jariya Wajahat Biochemistry of gastrointestinal tract
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. Allah gives without stint to whom he will.
37 the family of ImranAl-Qur’an
Dr Jariya Wajahat Biochemistry of gastrointestinal tract
DIETCarbohydrates
Dr Jariya Wajahat Biochemistry of gastrointestinal tract
Dietary carbohydrates
• Largest source of calories – 40-45%
• Plant– starch ( grains, tubers, veggies )
sucroseglucose fructosedietary fiber
• Animal– glycogen
glycolipidslactose
Dr Jariya Wajahat Biochemistry of gastrointestinal tract
Carbohydrates in our diet
α-D-glucose
OH
OH
OH
CH₂OH
OH
O OH
OH
OH
CH₂OH
OH
β-D-glucose
O
Dr Jariya Wajahat Biochemistry of gastrointestinal tract
Carbohydrates in our diet
α-D-glucose
OH
OH
OH
CH₂OH
OH
OH
OH
OH
CH₂OH
OH
β-D-galactose
O O
Dr Jariya Wajahat Biochemistry of gastrointestinal tract
Carbohydrates in our diet
β-D-fructose
OH
OH
CH₂OH
OHOCH₂
OH
α-D-glucose
OH
OH
OH
CH₂OH
OH
O
Dr Jariya Wajahat Biochemistry of gastrointestinal tract
Carbohydrates in our diet
α-D-glucoseβ-D-glucose
OH
OH
CH₂OH
OH
OH
CH₂OH
O O
Dr Jariya Wajahat Biochemistry of gastrointestinal tract
Carbohydrates in our diet
α-D-glucoseβ-D-galactose
O
OH
OH
CH₂OH
OH
OH
CH₂OH
O
Dr Jariya Wajahat Biochemistry of gastrointestinal tract
Carbohydrates in our diet
β-D-fructose α-D-glucose
OH
CH₂OH
OHOCH₂
OH
O
OH
OH
CH₂OH
OH
Dr Jariya Wajahat Biochemistry of gastrointestinal tract
Carbohydrates in our diet
α-D-glucose
O
OH
OH
CH₂OH
α-D-glucose
O
OH
OH
CH₂
Dr Jariya Wajahat Biochemistry of gastrointestinal tract
Carbohydrates in our diet
O
O
O
β-D-fructose
α-D-glucose
Sucrose
So what’s our relationship?
Its called α-1—2 glycosidic bond
Dr Jariya Wajahat Biochemistry of gastrointestinal tract
Carbohydrates in our diet
Lactose
O OO
So what’s our relationship?
Its called β-1—4 glycosidic bond
Dr Jariya Wajahat Biochemistry of gastrointestinal tract
Carbohydrates in our diet
Maltose
OO
O
So what’s our relationship?
Its called α-1—4 glycosidic bond
Dr Jariya Wajahat Biochemistry of gastrointestinal tract
Carbohydrates in our diet
Maltotriose
OO
O
O
O
So what’s our relationship?
Of course! It’s the α-1—4 glycosidic
linkages
Dr Jariya Wajahat Biochemistry of gastrointestinal tract
Carbohydrates in our diet
Iso- maltose
O
O
O
So what’s our relationship?
Its called α-1—6 glycosidic bond
Dr Jariya Wajahat Biochemistry of gastrointestinal tract
Carbohydrates in our diet
Trehalose
OO
O
So what’s our relationship?
Its called α-1—1 glycosidic bond ,
is’nt it cool?
Dr Jariya Wajahat Biochemistry of gastrointestinal tract
Carbohydrates in our diet
Lactulose
OO
O
O OO
So what’s our relationship?
Its called β-1—2 glycosidic bond
I don’t understand!
Dr Jariya Wajahat Biochemistry of gastrointestinal tract
Carbohydrates in our diet
OO
O
O
OO O
Amylose
We’ve got a strong
relashionship, the α-1—4 glycosidic
linkage
Dr Jariya Wajahat Biochemistry of gastrointestinal tract
Carbohydrates in our diet
OO
O
O
OO O
Amylo-pectin
O
O
O
OWe are stronger, we
have got α-1—4 glycosidic linkages
as well α-1—6 branch points
Dr Jariya Wajahat Biochemistry of gastrointestinal tract
Carbohydrates in our diet
Cellulose
O O
OO
O
O
OO
We are a team, we have got the β-1—4 glycosidic linkages!
Dr Jariya Wajahat Biochemistry of gastrointestinal tract
DIGESTIONCarbohydrates
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
Salivary α-amylase
O
O
OO
OO
OO
OO
OO
OO
OO
OO
OO
α-limit dextrins
Shortened polysaccharides
Dr Jariya Wajahat Biochemistry of gastrointestinal tract
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 O
OO
OO
OO
O
4-9 glycosyl residues and 1 or more 1,6 branches
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
• Highest activity in ileum
OO
OO
OO
OO
OO
O OO
OO
OO O
Dr Jariya Wajahat Biochemistry of gastrointestinal tract
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
Maltose
OO
O
Dr Jariya Wajahat Biochemistry of gastrointestinal tract
Sucrase-isomaltase complex
Iso- maltose
O
O
O
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 β1,4 bonds b/w glucose and galactose
• Jejunum
Dr Jariya Wajahat Biochemistry of gastrointestinal tract
β-glycosidase complex
O OO
Dr Jariya Wajahat Biochemistry of gastrointestinal tract
Glycolipids
• Cerebrosides – Ceramide-monosaccharides
• Globosides – Ceramide-oligosaccharides
GLU CERAMIDE
GAL CERAMIDEGLU
Dr Jariya Wajahat Biochemistry of gastrointestinal tract
Glycolipids
• Forssman antigen – Ceramide-oligosaccharides
GAL CERAMIDEGLUGALGALNAcGALNAc
Dr Jariya Wajahat Biochemistry of gastrointestinal tract
Trehalase
• Splits α1,1 bond in trehalose• Found in mushrooms,insects and seafood
Trehalose
OO
O
Dr Jariya Wajahat Biochemistry of gastrointestinal tract
ABSORPTION Carbohydrates
Dr Jariya Wajahat Biochemistry of gastrointestinal tract
Absorption of monosaccharides
• Glucose • Fructose • Galactose
• Site – Duodenum– Upper jejunum
O
O
O
Hi!
Dr Jariya Wajahat Biochemistry of gastrointestinal tract
GLUT 5
GLUT 2
3Na+
2K+
O
Na+
O
Na+
Na+
Na+
Na+
Na+
O
SGLT-1
O
ONa+
O
Dr Jariya Wajahat Biochemistry of gastrointestinal tract
GLUT 5
GLUT 2
O
Na+
O
Na+
Na+
Na+
Na+
Na+
O
SGLT-1O
Na+
O
GLUT 2O
Dr Jariya Wajahat Biochemistry of gastrointestinal tract
INDIGESTIBLE Carbohydrates
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
– H2, CO2, 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
DISORDERS Carbohydrates
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– 45min-1hr 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
DIAGNOSISCarbohydrate disorders
Dr Jariya Wajahat Biochemistry of gastrointestinal tract
Disorders of carbohydrate digestion and absorption
• Diagnosis – Oral tolerance tests– H2 breath test
Dr Jariya Wajahat Biochemistry of gastrointestinal tract
TREATMENT Carbohydrate disorders
Dr Jariya Wajahat Biochemistry of gastrointestinal tract
Treatment
• Avoid foods containing specific disaccharide• Tablets and capsules containing enzymes