digestion and absorption
DESCRIPTION
Digestion and absorption. Carbohydrates. 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 Imran Al-Qur’an. - PowerPoint PPT PresentationTRANSCRIPT
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Dr Jariya Wajahat Biochemistry of gastrointestinal tract
Digestion and absorption
Carbohydrates
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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
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Dr Jariya Wajahat Biochemistry of gastrointestinal tract
DIETCarbohydrates
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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
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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
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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
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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
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Dr Jariya Wajahat Biochemistry of gastrointestinal tract
Carbohydrates in our diet
α-D-glucoseβ-D-glucose
OH
OH
CH₂OH
OH
OH
CH₂OH
O O
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Dr Jariya Wajahat Biochemistry of gastrointestinal tract
Carbohydrates in our diet
α-D-glucoseβ-D-galactose
O
OH
OH
CH₂OH
OH
OH
CH₂OH
O
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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
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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
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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
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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
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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
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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
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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
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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?
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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!
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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
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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
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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!
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Dr Jariya Wajahat Biochemistry of gastrointestinal tract
DIGESTIONCarbohydrates
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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
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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
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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
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Dr Jariya Wajahat Biochemistry of gastrointestinal tract
Stomach
• Salivary alpha amylase– Inactivated by gastric HCl
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Dr Jariya Wajahat Biochemistry of gastrointestinal tract
Small intestine
• Pancreatic alpha amylase• Bicarbonate• Intestinal disaccharidases
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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
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Dr Jariya Wajahat Biochemistry of gastrointestinal tract
Intestinal disaccharidases
• Glucoamylase• Sucrase isomaltase complex• Lactase glucosylceramidase/ β-glycosidase
complex • Trehalase
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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
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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
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Dr Jariya Wajahat Biochemistry of gastrointestinal tract
Sucrase-isomaltase complex
O
O
O
Sucrose
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Dr Jariya Wajahat Biochemistry of gastrointestinal tract
Sucrase-isomaltase complex
Maltose
OO
O
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Dr Jariya Wajahat Biochemistry of gastrointestinal tract
Sucrase-isomaltase complex
Iso- maltose
O
O
O
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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
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Dr Jariya Wajahat Biochemistry of gastrointestinal tract
β-glycosidase complex
O OO
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Dr Jariya Wajahat Biochemistry of gastrointestinal tract
Glycolipids
• Cerebrosides – Ceramide-monosaccharides
• Globosides – Ceramide-oligosaccharides
GLU CERAMIDE
GAL CERAMIDEGLU
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Dr Jariya Wajahat Biochemistry of gastrointestinal tract
Glycolipids
• Forssman antigen – Ceramide-oligosaccharides
GAL CERAMIDEGLUGALGALNAcGALNAc
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Dr Jariya Wajahat Biochemistry of gastrointestinal tract
Trehalase
• Splits α1,1 bond in trehalose• Found in mushrooms,insects and seafood
Trehalose
OO
O
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Dr Jariya Wajahat Biochemistry of gastrointestinal tract
ABSORPTION Carbohydrates
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Dr Jariya Wajahat Biochemistry of gastrointestinal tract
Absorption of monosaccharides
• Glucose • Fructose • Galactose
• Site – Duodenum– Upper jejunum
O
O
O
Hi!
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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
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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
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Dr Jariya Wajahat Biochemistry of gastrointestinal tract
INDIGESTIBLE Carbohydrates
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Dr Jariya Wajahat Biochemistry of gastrointestinal tract
Indigestible carbohydrates
• Cellulose • Hemicelluloses • Gums • Mucilages • Pectin • Raffinose • Lignin
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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
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Dr Jariya Wajahat Biochemistry of gastrointestinal tract
• What is the cause of excessive flatulence after having a meal containing beans?
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Dr Jariya Wajahat Biochemistry of gastrointestinal tract
DISORDERS Carbohydrates
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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
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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
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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
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Dr Jariya Wajahat Biochemistry of gastrointestinal tract
• Yogurt is a dairy product, why is it recommended in lactose intolerance?
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Dr Jariya Wajahat Biochemistry of gastrointestinal tract
Disaccharide intolerance
• Etiology – Hereditary deficiency– Injured Mucosa• Disease, drugs, malnutrition
• Clinical features – Osmotic diarrhea – Abdominal cramps– Flatulence
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Dr Jariya Wajahat Biochemistry of gastrointestinal tract
Sucrase-isomaltase complex deficiency
• intolerance of ingested sucrose
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Dr Jariya Wajahat Biochemistry of gastrointestinal tract
Defect in absorption of fructose
• Clinical features– Gas and distented abdomen after eating fruit,
sweets or juices
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Dr Jariya Wajahat Biochemistry of gastrointestinal tract
DIAGNOSISCarbohydrate disorders
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Dr Jariya Wajahat Biochemistry of gastrointestinal tract
Disorders of carbohydrate digestion and absorption
• Diagnosis – Oral tolerance tests– H2 breath test
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Dr Jariya Wajahat Biochemistry of gastrointestinal tract
TREATMENT Carbohydrate disorders
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Dr Jariya Wajahat Biochemistry of gastrointestinal tract
Treatment
• Avoid foods containing specific disaccharide• Tablets and capsules containing enzymes