Biochemistry-6-1-carbohdrates 1 6. Carbohydrates Carbohydrates are aldehyde or ketone compounds with multiple hydroxyl groups. They make up most of the organic matter on Earth because of their extensive roles in all forms of life Chapter 4: Outline 6.1 Monosaccharides are aldehydes and ketones with multiple hydroxyl groups 6.2 Complex carbohydrates are formed by linkage of monosaccharides 6.3 Carbohydrates can be attached to proteins to form glycoproteins 6.4 Lectins are specific carbohydrate-binding proteins Biochemistry-6-1-carbohdrates 2 Properties of Carbohydrates 1. Carbohydrates serve as energy stores, fuels, & metabolic intermediates 2. Ribose & deoxyribose sugars form part of the structural framework of RNA & DNA 3. Polysaccharides are structural elements in the cell walls of bacteria and plants. Cellulose is the most abundant organic compound in the biosphere 4. Carbohydrates are linked to many proteins and lipids, key role in mediating interactions among cells - made possible by their huge structural diversity Biochemistry-6-1-carbohdrates 3 Monosaccharides Simplest carbohydrates, aldehydes or ketones with two or more hydroxyl groups Empirical formula, (C-H2O)n, literally a “carbon hydrate” Smallest monosaccharides are trioses (n = 3) Glyceraldehyde has 1 asymmetric C, thus, 2 stereoisomers (D- & L-), are enantiomers, mirror images of each other Keto group Aldehyde group Biochemistry-6-1-carbohdrates 4 Dihydroxyacetone Keto group No asymmetric carbon Biochemistry-6-1-carbohdrates 5 D-Glyceraldehyde Aldehyde group Asymmetric carbon Biochemistry-6-1-carbohdrates 6 L-Glyceraldehyde Aldehyde group Asymmetric carbon Biochemistry-6-1-carbohdrates 7 Fischer Projections Horizontal bonds; in front of page plane Vertical bonds; behind plane Stereochemical relations: Biochemistry-6-1-carbohdrates 8 D-Aldoses (3,4,5, & 6 carbons) Aldehyde group, blue Distal asymmetric center Numbering Biochemistry-6-1-carbohdrates 9 Triose & tetroses Aldehyde group, blue Distal asymmetric center Note numbering Biochemistry-6-1-carbohdrates 10 Tetrose & Pentoses Biochemistry-6-1-carbohdrates 11 Tetrose & Pentoses Biochemistry-6-1-carbohdrates 12 Pentoses & Hexoses Biochemistry-6-1-carbohdrates 13 Pentoses & Hexoses Biochemistry-6-1-carbohdrates 14 D-Ketoses (3,4,5, & 6 carbons) Keto group, blue Distal asymmetric center Numbering Biochemistry-6-1-carbohdrates 15 Triose & tetrose Biochemistry-6-1-carbohdrates 16 Tetrose & Pentoses Biochemistry-6-1-carbohdrates 17 Pentoses & Hexoses Biochemistry-6-1-carbohdrates 18 Aldehydes cyclize (pentoses & hexoses) An aldehyde can react with an alcohol to form a hemiacetal Biochemistry-6-1-carbohdrates 19 Ketones cyclize (pentoses & hexoses) A ketone can react with an alcohol to form a hemiketal Biochemistry-6-1-carbohdrates 20 5 & 6 membered rings Furanose Pyranose Biochemistry-6-1-carbohdrates 21 Pyranose formation Fischer projection Intramolecular hemiacetal, 2 anomers,  &  at C1 Haworth projection D & L enantiomers at C5 Biochemistry-6-1-carbohdrates 22 Furanose formation (from hexose) Fischer projection D & L enantiomers at C5 Intramolecular hemiketal, 2 anomers,  &  at C2 Haworth projection Biochemistry-6-1-carbohdrates 23 Furanose formation (from pentoses) D & L enantiomers at C4 C-1 is anomeric carbon, -anomer, OH below ring plane -anomer, OH above the plane Biochemistry-6-1-carbohdrates 24 Fructose ring structures C5 to C2 bond C6 to C2 bond Biochemistry-6-1-carbohdrates 25 C5, D C2, -D-Fructofuranose Biochemistry-6-1-carbohdrates 26 -D-Fructofuranose C2,  Biochemistry-6-1-carbohdrates 27 -D-Fructopyranose C5, D C2,  Biochemistry-6-1-carbohdrates 28 -D-Fructopyranose C5, D C2, -anomer Biochemistry-6-1-carbohdrates 29 Pyranose ring not planer Biochemistry-6-1-carbohdrates 30 Chair & Boat forms Biochemistry-6-1-carbohdrates 31 Furanose ring not planer Envelope form of -D-ribose Biochemistry-6-1-carbohdrates 32 Reducing sugars Solution of cupric ion, Cu2+ (Fehling’s solution), test for reducing sugars such as glucose Free aldehyde group is oxidized Biochemistry-6-1-carbohdrates 33 Glycosidic bonds Monosaccharides can react with alcohols & amines D-glucose + methanol (acid-catalyzed), two products,  &  Biochemistry-6-1-carbohdrates 34 Modified monosaccharides Frequently expressed on cell surfaces Biochemistry-6-1-carbohdrates 35 Biochemistry-6-1-carbohdrates 36 Biochemistry-6-1-carbohdrates 37 Biochemistry-6-1-carbohdrates 38 Biochemistry-6-1-carbohdrates 39 Linkage of monosaccharides: Maltose, a disaccharide C1 C6 C6 2 glucose molecules linked by an -1,4-glycosidic bond Biochemistry-6-1-carbohdrates 40 Common disaccharides Common dietary components Biochemistry-6-1-carbohdrates 41 Sucrose (table sugar from cane or beet) Hydrolyzed by sucrase Biochemistry-6-1-carbohdrates 42 Lactose (from milk) Hydrolyzed by lactase in humans, & by -galactosidase in bacteria Biochemistry-6-1-carbohdrates 43 Maltose (from starch hydrolysis) Hydrolyzed by maltase Biochemistry-6-1-carbohdrates 44 EM of microvillus (in small intestine) Sucrase, lactase, & maltase, located on microvilli (project from outer face of plasma membrane of intestinal epithelial cells) Biochemistry-6-1-carbohdrates 45 Polysaccharides: Glycogen (branch points) Branch every 10 glucose units (approx) Glycogen is highly branched Glucose store Biochemistry-6-1-carbohdrates 46 Glycosidic bonds determine structure Straight chains, good for structureBent chains, good for storage Biochemistry-6-1-carbohdrates 47 Cellulose Major structural polymer of plants, one of the most abundant organic compounds in the biosphere Straight chain polymer of glucose, Fibrils formed by parallel chains, held by hydrogen bonds Mammals lack cellulases, cannot digest wood or vegetable fibers, bacteria hydrolyze it in the rumen Biochemistry-6-1-carbohdrates 48 Starch & glycogen (homopolymers) Open helix, accessible stores of sugar, starch in plants, glycogen in animals Glycogen, highly branched, (every 10 glucose units)Starch, two forms, Amylose - unbranched, Amylopectin - branched (every 30 glucose units) Biochemistry-6-1-carbohdrates 49 Glycosaminoglycans, Anionic Polysaccharides Made of repeating disaccharide units, containing a derivative of an amino sugar, glucosamine or galactosamine At least 1 of the sugars has a negatively charged carboxyl or sulfate group Usually attached to proteins to form proteoglycan (95% carb) Biochemistry-6-1-carbohdrates 50 Proteoglycan functions • Lubricants for mucous membranes & connective tissue • Structural components in connective tissue • Mediate adhesion of cells to extracellular matrix • Bind factors that stimulate cell proliferation Biochemistry-6-1-carbohdrates 51 Chondroitin 6-sufate Found in cartilage Biochemistry-6-1-carbohdrates 52 Keratan sulfate Found in hair, nails, etc Biochemistry-6-1-carbohdrates 53 Heparin Anticoagulant used to prevent blood clotting Biochemistry-6-1-carbohdrates 54 Dermatan sulfate Found in skin Biochemistry-6-1-carbohdrates 55 Hyaluronate Found in connective tissue & serves as lubricant Biochemistry-6-1-carbohdrates 56 Oligosaccharide synthesis: Glycosyltransferases Catalyze formation of glycosidic bonds, Each enzyme specific to sugar, Therefore, many enzymes required Unlike nucleic acid or protein biosynthesis, no template used Biochemistry-6-1-carbohdrates 57 Activated sugar nucleotide Important intermediates in many processes Biochemistry-6-1-carbohdrates 58 Glycosidic bond formed Biochemistry-6-1-carbohdrates 59 A, B, & O oligosaccharide antigens (blood groups) Foundation oligo(frameshift mutant gene), one from each parent Specific glycosyltransferases add group to O antigen Biochemistry-6-1-carbohdrates 60 Glycoproteins (small % of carbs), glycosidic bonds N-linked, Asn in ER & Golgi O-linked, Ser, Thr in Golgi only Components of cell membranes, adhesion, binding of sperm to eggs Some soluble proteins also Biochemistry-6-1-carbohdrates 61 N-linked oligos, high mannose type Biochemistry-6-1-carbohdrates 62 N-linked oligos, complex Biochemistry-6-1-carbohdrates 63 Elastase,secreted glycoprotein in serum Most proteins in blood serum are glycoproteins Biochemistry-6-1-carbohdrates 64 ER & Golgi complex Electron micrograph Where proteins are glycosylated following synthesis on ribosomes N-linked in ER O-linked in Golgi Black dots on ER are ribosomes Biochemistry-6-1-carbohdrates 65 Transport into ER Glycosylation starts in ER lumen Biochemistry-6-1-carbohdrates 66 Repeating unit of Dolichol Phosphate (in ER membrane) DP, specialized lipid in ER membrane - up to 20 isoprene Biochemistry-6-1-carbohdrates 67 Dolichol phosphate In ER membrane, phosphate group on cytoplasmic face A lipid molecule on which oligosaccharides are assembled prior to protein glycosylation Biochemistry-6-1-carbohdrates 68 Assembly of N-linked oligos on Dol-P Three stages Cytoplasmic Flip ER lumem Biochemistry-6-1-carbohdrates 69 Golgi complex, sorting center Targets proteins to, Lysosomes, Secretory vesicles, Plasma membrane Biochemistry-6-1-carbohdrates 70 Mannose 6-phosphate marker Modification of mannose residue in the oligo as a marker for targeting to Lysosomes Done in cis Golgi compartment Biochemistry-6-1-carbohdrates 71 Step one Phospho-N-acetylglucosamine Biochemistry-6-1-carbohdrates 72 Step two Biochemistry-6-1-carbohdrates 73 Quality control of protein folding in ER Calnexin, & (calreticulin) chaparone Proteins Carbohydrates carry information Biochemistry-6-1-carbohdrates 74 Oligo structure by mass spectrometry Biochemistry-6-1-carbohdrates 75 Plant lectins, binding selectivities Three plant lectins bind different oligos serve as insecticides Biochemistry-6-1-carbohdrates 76 Animal lectin, C-type carb-binding domain Animal cell lectins facilitate cell-cell contact Lectin binding sites on surface of one cell interacts with carbs displayed on surface of another cell (like Velcro) In animal cell C-type lectins, Ca2+ ion acts as a bridge between protein and sugar residue of oligo Biochemistry-6-1-carbohdrates 77 Selectins, C-type lectins Lymphocytes binding to lining of lymph nodes Bind immunesystem cells to targets, L- to lymphnode vessels, E- to endothelium, P- to blood platlets Biochemistry-6-1-carbohdrates 78 Influenza hemagglutinin Binds to sialic acid residues on target cell surface, Inside cell, viral protein, neuraminidase, cleaves glycosidic bond; a promising target for anti-influenza agents