disaccharides
• Sucrose: glucose+fructose
(from suger cane or sugar beet),
hydrolyzed by sucrase
• Lactose: galactose+glucose
(from milk)
hydrolyzed by lactase
• Maltose: glucose+glucose
(from starch)
hydrolyzed by maltase
QuickTime™ and a
TIFF (U ncompressed) decompressor
are needed to see this pi cture.
In animals,
sucrase, lactase and maltase are located
on the outer surfaces of epithelial cells
lining the small intestine.
Brach point in glycogen.
Glycogen
Glycogen is stored in liver and in skeletal
muscle
Starch and Cellulose
cellulose
• Cellulose is one o the most abundant organic
compounds in the biosphere.
• It is an unbranched polymer of glucose residues
joined by -1,4-linkages.
• Mammals lack cellulases and therefore cannot digest
wood and vegetable fibers.
• Soluble fibers, pectin, slows the movement of food
through the gastrointestinal track. Increases better
digestion and absorption of nutrients.
• Insoluble fibers, cellulose increase the rate at which
digestion products pass through the large intestine.
Minimizes exposure to toxins in our diet.
Structures or five repeating units of
important glpycosaminoglycans
Proteoglycans
• Proteoglycans are proteins attached to a
particular type of polysaccharides.
• (about 95% sugar, 5% protein)
• Cartilage
(made of aggrecan and collagen)
• Shock-absorber
• Osteoarthritis result from the proteolytic
degredation of aggrecan and collagen in the
cartilage.
Electron micrograph of proteoglycan
from cartilage
A, B and O antigens in blood groups
Each person inherits the gene for one of the
glycosyltransferases from each parent. Type A
transferase adds N-acetylgalactosamine, whereas the
type B transferase adds galactose.
• Evolutionary perspective:
Why different blood types present
in the human population?
Erythropoietin: a glycoprotein
• EPO is secreted by the
kidneys and stimulates
the production of red
blood cells. Availability
of recombinant human
EPO has greatly aided
the treatment of
anemias
• The mature EPO is
40% carbohydrate by
weight. Unglycosylated
protein has only 10%
bioactivity.
Fat synthesis
Two most common fatty acids
in humans
Phospholipid bilayer membrane
• Fovured structure for
most phospholipids in
aquous media is a
bimolecular sheet.
• Lipid bilayers form
spontaneously by a
self-assembly process.
• Hydrophobic
interactions are the
major driving force.
Membrane fluidity
• Membrane fluidity is controlled by fatty acid
composition and cholesterol content. Melting
temperature depends on the leghth of the fatty acid
chains and on their degree of unsaturation.
Cell membranes
Rhodopsin:
a 7-transmembrane helix protein
porin