chapter 11. carbohydrates - personal.tcu.edupersonal.tcu.edu/yryu/50133/carbohydrates.pdf · •...
TRANSCRIPT
Chapter 11. Carbohydrates
• Monosaccharides• Oligosaccharides• Polysaccharides• Glycoproteins
Carbohydrates
• Gluconeogenesis and photosynthesis• Oxidation of carbohydrates provides
energy to sustain life• Energy storage — starch or glycogen• Structural function – cellulose, chitin
peptidoglycan & glycosaminoglycans• Glycoconjugates - glycoproteins &
glycolipids
• Chemical nature of carbonyl group– Aldose : carbonyl is an aldehyde– Ketose : carbonyl is a ketone
• Number of carbon atoms– Trioses (C3)– Tetroses (C4)– Pentoses (C5)– Hexoses (C6)– Heptoses (C7)– etc
Classification of monosaccharides
D-Aldoses
D-Ketoses
ketotetrose
ketotriose
ketopentoses
ketohexoses
EpimersSugars that differ only by the configuration around one carbon atom
Hemiacetals and hemiketals
Cyclization of monosaccharides
Cyclic sugars have two anomeric forms
β-anomerα-anomer
Sugars are conformationally variable
Two chair conformations of β-D-glucopyranose
Sugar derivatives
• Aldonic acids – oxidation of an aldehydegroup in an aldose to an carboxylic acid
• Uronic acids – oxidation of a primary alcohol group to an carboxylic acid
• Alditols – reduction of aldoses and ketoses• Deoxy sugars – replacement of OH with H• Amino sugars – replacement of OH with
NH2• Sugar phosphates
Aldonic acids and uronic acids
D-Glucuronic acidD-Glucose D-Gluconic acid
Alditols
Deoxy sugars
Amino sugars
Sialic acids(NAM)
Sugar phosphates
O-Glycosides
N-Glycosides
French Fries à la Plastic
Neurotoxin and suspected carcinogen !!!
Disaccharides
Artificial sweeteners
SucraloseAspartameSaccharin
Polysaccharides (Glycans)
Polymers of monosaccharides linked together by glycosidic bonds
• Homo or heteropolysaccharides• Linear or branched polysaccharides
Storage polysaccharides
• Starch – Plant• Glycogen – Animal
Starch granule in plant cell chloroplasts Glycogen granule in liver cells
Starch
Helical structure of amylose
Glycogen
Structure of amylopectin or glycogen
Structural polysaccharides• Cellulose
– Plant cell walls– Marine invertebrates (Tunicates)
• Chitin– Exoskeletons of invertebrates (Crustaceans, Insects,
Spiders)– Cell walls of most fungi and many algae
• Glycosaminoglycan (=Mucopolysaccharides)– Connective tissues (Cartilage and tendons) or
extracellular matrix (ground substance) of higher animals
Cellulose
n
Glucose Glucose
Chitin
Glycosaminoglycans (Mucopolysaccharides)
n n
n n
n n
Glycosaminoglycans• Hyaluronic acid – connective tissue, synovial
fluids, vitreous humor of the eye• Chondroitin sulfate – cartilage and other
connective tissue• Dermatan sulfate – skin • Keratan sulfate • Heparin – component of intracellular granules of
the mast cells (blood-clotting inhibitor)• Heparan sulfate – cell surface and extracellular
substance in blood vessel and brain (interaction with fibroblast growth factors and their receptors)
Glycoproteins
• Proteoglycans• Peptidoglycans• Glycosylated proteins
Proteoglycans
Bacterial cell walls
Peptidoglycans
Antibiotics targeting peptidoglycans
Glycosylated proteins
• Proteins often contain oligo or polysaccharides
• Sugar modification are mostly seen in extracellular or transmembrane proteins
• Protein can contain 10-90% carbohydrates• Carbohydrates are usually linked through
asparagine (N-linked), or serine or threonine (O-linked)
O- and N-linked oligosaccharides
Oligosaccharide dynamics
Turnover of serum proteins
Cell surface
Lectins
Proteins that specifically recognize carbohydrate
ABO blood types