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Carbohydrate Structure and metabolism Harvey RA, Champe PC. Lippincott Illustrated Biochemistry 3rd Edition, 2005 Definition CHO (Hydrated carbon) • CHO are aldehyde or ketone (=O) compounds with multiple hydroxy (-OH) groups • General formula (CH2O)n • Monosaccharides and Disaccharides are called sugars, they end by – OSE e.g. glucose, lactose etc. Harvey RA, Champe PC. Lippincott Illustrated Biochemistry 3rd Edition, 2005 Functional groups • C-OH, hydroxyl group • C=O, carbonyl group • OH • C=O, carboxyl group Harvey RA, Champe PC. Lippincott Illustrated Biochemistry 3rd Edition, 2005 Functions • Provision of energy • Storage of energy • Major component in nucleic acid structure • Structural functions, cell wall (bacteria and plants) • Cell membrane (Signal transduction – adhesion, cell-cell interaction and etc) • Others e.g. mucin Harvey RA, Champe PC. Lippincott Illustrated Biochemistry 3rd Edition, 2005 • Glucose Figure 4.6 Mannose and galactose are epimers of glucose Harvey RA, Champe PC. Lippincott Illustrated Biochemistry 3rd Edition, 2005 Classification • Monosaccharides (simplest unit) • Disaccharides: 2 monosaccharides linked by covalent glycosidic bond e.g. sucrose • Oligosaccharides: 3 – 10 monomers • Polysaccharides: more than 10 could be linear or branched Harvey RA, Champe PC. Lippincott Illustrated Biochemistry 3rd Edition, 2005 Monosaccharides (simplest unit) • A . Aldose • • • • • • Trioses Tetroses Pentoses Hexoses Heptoses Nonoses b. Ketose [3] [4] [5] [6] [7] [9] Harvey RA, Champe PC. Lippincott Illustrated Biochemistry 3rd Edition, 2005 Harvey RA, Champe PC. Lippincott Illustrated Biochemistry 3rd Edition, 2005 Harvey RA, Champe PC. Lippincott Illustrated Biochemistry 3rd Edition, 2005 Hexoses [C6] (Isomers) • Isomers; are sugars have the same chemical formula (CH2O)n, but have different structures • Enantiomers (mirror images; L or D) (position of OH on asymmetric carbons furthest from =O group) • Anomers: OH above () or below () plane around anomeric C (C to which attached the =O) e.g. C1 in glucose, C2 in fructose • Epimers: they differ in orientation (right or left) of one OH around asymmetric C (C2 to C5) Harvey RA, Champe PC. Lippincott Illustrated Biochemistry 3rd Edition, 2005 Enantiomers have identical chemical and physical properties except for their ability to rotate planepolarized light by equal amounts but in opposite directions. Harvey RA, Champe PC. Lippincott Illustrated Biochemistry 3rd Edition, 2005 Figure 4.7 Formation of ring structures in sugars Harvey RA, Champe PC. Lippincott Illustrated Biochemistry 3rd Edition, 2005 Harvey RA, Champe PC. Lippincott Illustrated Biochemistry 3rd Edition, 2005 • Monosacchrides form cyclic structure (ring) in solution (=O react with -OH in the same molecule) • Formed Glu ring is called pyranose (pyran like) • In this case the C1 is called anomeric C • If the OH attached to C1 above the ring plane, we say -anomer, if below is -anomer • In solution -and - interchange (mutarotation) • Keto sugars form (furan like) furanoses Harvey RA, Champe PC. Lippincott Illustrated Biochemistry 3rd Edition, 2005 Figure 4.6 Mannose and galactose are epimers of glucose Harvey RA, Champe PC. Lippincott Illustrated Biochemistry 3rd Edition, 2005 Harvey RA, Champe PC. Lippincott Illustrated Biochemistry 3rd Edition, 2005 Bonds (linkage) • Monosaccharides interact with each other or other compound through glycosidic bonds • Glycosidic bond is covalent bond between the anomeric C (in glucose C1) and C of another compound • The glycosidic bond can be O- or Nglycosidic bond Harvey RA, Champe PC. Lippincott Illustrated Biochemistry 3rd Edition, 2005 Harvey RA, Champe PC. Lippincott Illustrated Biochemistry 3rd Edition, 2005 Disaccharides Name Source Disaccharide (glycoside) Abbreviation Lactose Milk galactose β(1,4) glucose Gal β(1,4) Glc Sucrose* Sugar cane glucose α(1,2) β-fructose Glc α(1,2) β-Fru Trehalose* Insects glucose α(1,1) α-glucose Glc α(1,1) α-Glc Maltose Starch glucose α(1,4) glucose Glc α(1,4) Glc Glucose β(1,4) glucose Glc β(1,4) Glc Cellobiose* Cellulose Harvey RA, Champe PC. Lippincott Illustrated Biochemistry 3rd Edition, 2005 Polysaccharides 1. Cellulose: - Found in plant cell walls - Composed of glucose units - linear structure - 1-4 linkages - Insoluble - Humans can not hydrolyze the 1-4 bonds, so not digestible in humans - Important in our diet – decrease constipation and colon cancer Harvey RA, Champe PC. Lippincott Illustrated Biochemistry 3rd Edition, 2005 Cellulose Structure Figure 4.9 The β1,4 glycosidic bonds in cellulose Harvey RA, Champe PC. Lippincott Illustrated Biochemistry 3rd Edition, 2005 Polysaccharides 2. Starches • Plant origin • Polysaccharides of long chain polymers of - D-glucose • Have un-branched chains (amylose; 20%); glucose units linked by -1-4 links • In branched chains part (amylopectin; 80%); in addition to -1-4 links there are -1-6 links at branch points Harvey RA, Champe PC. Lippincott Illustrated Biochemistry 3rd Edition, 2005 Figure 4.10 The structures of amylose and Amylopectin Harvey RA, Champe PC. Lippincott Illustrated Biochemistry 3rd Edition, 2005 Polysaccharides 3. Glycogen • Animal origin (animal starch) • Storage form of CHO in human cells, found as glycogen granules (also contain enzymes of synthesis & degradation) • Polysaccharides of long chain polymers of - D-glucose • Similar to amylopectin of starch but much more branched • Multiple Branches; to provide many nonreducing ends for quick release of glucose Harvey RA, Champe PC. Lippincott Illustrated Biochemistry 3rd Edition, 2005 Polysaccharides • Most tissues contain glycogen, But liver (10%wt), and muscles (2%wt), store most of body glycogen • The muscle glycogen is for local use of the muscles, it CAN NOT be released in blood • Liver glycogen is to maintain blood glucose Harvey RA, Champe PC. Lippincott Illustrated Biochemistry 3rd Edition, 2005 Polysaccharides 4. Inulin • Is plant starch, found in tuber and root of certain plants • A polymer of fructose • The linkage is (2-1) • Soluble in warm water • Has been used to measure renal glomerular filtration rate Harvey RA, Champe PC. Lippincott Illustrated Biochemistry 3rd Edition, 2005 Reducing sugars • The free anomeric C (aldhyde or keto group ) of the open-chain form of sugar can reduce Cu2+ (cupric) to Cu+ (cuprous) in alkaline solutions (Fehling or Benedict test) • Examples of reducing sugars are: glucose, galactose, fructose, maltose, and lactose • Non-reducing sugars: sucrose, cellobiose Harvey RA, Champe PC. Lippincott Illustrated Biochemistry 3rd Edition, 2005 Glycoproteins and proteoglycans Glycoproteins • Oligosaccharides or small polysacch. covalently linked to protein via N- or Oglycosidic bonds • Examples: blood groups, signal molecules Harvey RA, Champe PC. Lippincott Illustrated Biochemistry 3rd Edition, 2005 Glycoproteins and proteoglycans Proteoglycans • Large protein polysaccharides complex (ground substance of connective tissue) • The polysaccharides: are high MW, polyanionic glycosaminoglycans (repeated units of disaccharide, one of them is always amino sugar – glucosamine or galactosamine and the other is uronic acid) Harvey RA, Champe PC. Lippincott Illustrated Biochemistry 3rd Edition, 2005 Harvey RA, Champe PC. Lippincott Illustrated Biochemistry 3rd Edition, 2005 Digestion & absorption • Digest.: Break of glycosidic bonds of dioligo- and polysaccharides by different enzymes • Enzymes are glycosidases • In mouth: salivary -amylase, act on 1,4 glycosidic bonds in starch/glycogen • In intestine: pancreatic -amylase, like salivary but work at lower pH (stomach acids) • Both produce disaccharides e.g. maltose, isomaltose Harvey RA, Champe PC. Lippincott Illustrated Biochemistry 3rd Edition, 2005 Harvey RA, Champe PC. Lippincott Illustrated Biochemistry 3rd Edition, 2005 Harvey RA, Champe PC. Lippincott Illustrated Biochemistry 3rd Edition, 2005 Harvey RA, Champe PC. Lippincott Illustrated Biochemistry 3rd Edition, 2005 Absorption • Small intestine mucosal brush border secret disacchridases (break disaccharides), releasing monosaccharides, which are absorbed • Deficiency e.g. lactase, lead to lactose intolerance; lactose acted upon by bacteria causing diarrhea, distension and dehydration Harvey RA, Champe PC. Lippincott Illustrated Biochemistry 3rd Edition, 2005 Harvey RA, Champe PC. Lippincott Illustrated Biochemistry 3rd Edition, 2005 Transport of glucose in the cell • A. Na+-dependent: - Needs energy (Na+/K+ ATPase) - Carrier binds both Glu and Na+ transport them inside cells (against concentration gradient), then pump Na+ out in exchange with K+, using ATP as source for energy. • B. Na+-independent facilitated transport: mediated by glucose transporters (GLUT 1 to 14) located in cell membrane. Harvey RA, Champe PC. Lippincott Illustrated Biochemistry 3rd Edition, 2005 Glucose transporters Transporter Tissue location GLUT1 GLUT2 GLUT3 GLUT4 GLUT5 Brain, kidney, colon, RBC, placenta Liver, pancreatic B cell, small intestine, kidney Brain, kidney, placenta Heart, skeletal muscles, adipose tissue Small intestine Harvey RA, Champe PC. Lippincott Illustrated Biochemistry 3rd Edition, 2005 Figure 4.14 How a glucose transporter (GLUT) works. Note the conformational change upon binding glucose Harvey RA, Champe PC. Lippincott Illustrated Biochemistry 3rd Edition, 2005 Harvey RA, Champe PC. Lippincott Illustrated Biochemistry 3rd Edition, 2005