BIBC 120 Lecture Notes - Hepatic Portal System, Cereal Germ, Active Transport
24 May 2018
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Week 3.2
Plants store carbohydrates as starch
- Amylose (starch): A linear (unbranced) polysaccharide (a 1,4 glycosidic bonds)
- Amylopectin (starch): A branched polysaccharide (a1,4 and a 1,6 bonds)
- Food also contain polysaccharides that cannot be broken down by our digestive
systems.
- Cellulose is a major form of fiber (b1,4 glycosidic bonds cannot be digested by
mammalian enzymes)
o glucose connected with b 1-4 bonds, cannot be digested by mammalian enzymes
- Real food is a mix of protein, lipids, and carbs
o kernel of wheat
▪ germ: vitamins and minerals, lipid source
▪ endosperm: 90% starch 10% Gluten
▪ Bran: most of fiber
o Which parts are contained in white flour vs. whole wheat flour?
▪ wheat: whole kernel
▪ white: just endosperm (no germ and bran)
Digestion and Absorption of Carbohydrates (hydrolyzing glycosidic bonds) Enzymes
- salivary a-amylase (mouth) and pancreatic a-amylase (small intestine)
o cuts internal a 1,4 bonds to make dextrins
- maltase (small intestine) cuts maltose (2 units?) and maltotriose (3 units?) to free
glucose and a-limit dextrinase (small intestine) cut a1,6 bonds to maltotriose
o both in microvilli brush border of small intestine
ABSORPTION OF GLUCOSE (lumen of small intestine)
- SGLT1 (secondary active transport, symport): 1 glucose (against) and 2 Na+ (down) into
cell (enterocyte)
- GLUT2 (facilitated diffusion): glucose (down) out of cell to blood (hepatic portal system
circulated absorbed monosaccharides to the liver)
- Na+/K+ ATPase pump: 3 Na+ in, 2 K+ out (both against) maintains low concentration of
Na inside cell
- someone with cholera or excessive diarrhea (more effective to give IV fluids than oral
intake of water) because body cannot absorb water as effectively when dehydrated
- if no IV give sodium and glucose and water mixture (movement of solutes from lumen of
intestine into blood)
- sucrase (enzyme) breaks down sucrose to glucose and fructose
o GLUT 5 (facilitated diffusion): for transporting fructose into enterocyte, on apical
side
- lactase (enzyme) breaks down lactose to glucose and galactose
o galactose taken up by SGLT1 (same as glucose)
find more resources at oneclass.com
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Document Summary
Amylose (starch): a linear (unbranced) polysaccharide (a 1,4 glycosidic bonds) Amylopectin (starch): a branched polysaccharide (a1,4 and a 1,6 bonds) Food also contain polysaccharides that cannot be broken down by our digestive systems. Cellulose is a major form of fiber (b1,4 glycosidic bonds cannot be digested by mammalian enzymes: glucose connected with b 1-4 bonds, cannot be digested by mammalian enzymes. Digestion and absorption of carbohydrates (hydrolyzing glycosidic bonds) enzymes salivary a-amylase (mouth) and pancreatic a-amylase (small intestine: cuts internal a 1,4 bonds to make dextrins. Maltase (small intestine) cuts maltose (2 units?) and maltotriose (3 units?) to free glucose and a-limit dextrinase (small intestine) cut a1,6 bonds to maltotriose: both in microvilli brush border of small intestine. Sglt1 (secondary active transport, symport): 1 glucose (against) and 2 na+ (down) into cell (enterocyte) Glut2 (facilitated diffusion): glucose (down) out of cell to blood (hepatic portal system circulated absorbed monosaccharides to the liver)
