Biochemistry Lecture 3 PDF

Biochemistry Polysaccharides (Glycans) LECTURE (3) DR. El-Sawy 0  Biochemistry Polysac...

Biochemistry Polysaccharides (Glycans) LECTURE (3) DR. El-Sawy 0  Biochemistry Polysaccharides (Glycans) Def :  ˃10 monosaccharide units joined by glycosidic bond.  According to structure : Homo-polysaccharides Hetero-polysaccharides (homo-glycans) (hetero-glycans)  Only one type of  ˃ one type of Contain monosaccharide. monosaccharides.  Starch - Glycogen  Glycosaminoglycans.  Dextran - Dextrin  Agar. Include  Inulin - Cellulose  Proteoglycans. ‫نباتي & حيواني‬ ‫كسره & فتحه‬ GAP ‫في الخلية‬ Types :  According to function : Storage Structural polysaccharides polysaccharides  Starch - Glycogen  Cellulose.  Dextran - Dextrin  Agar. Include  Inulin ‫نباتي & حيواني‬ ‫كسره & فتحه‬ AGAR ‫خلية‬ ‫في‬ DR. El-Sawy 1  Biochemistry Polysaccharides (Glycans) 1. Starch 2. Glycogen (animal starch)  α-D glucose units (glucosan)  α-glucose units (glucosan). consists of 2 layers: 1. Amylose: Inner linear non  It is highly branched. branching layer. 2. Amylopectin: Outer highly Structure branched layer.  The branch points occur once  The branches occur once every 30 linkages. every 10 glucose units (more  Both are rapidly hydrolyzed branched than amylopectin). by salivary and pancreatic  Give a red violet color with amylase to maltose & dextrins iodine.  The most common storage  Major form of storage polysaccharide in plants. polysaccharides in animals & human body.  It is found in : a) Mainly in liver (10 % of Functions liver mass) b) Skeletal muscle (1-2 % of muscle mass).  In fasting: breakdown to glucose to maintain blood glucose level. DR. El-Sawy 2  Biochemistry Polysaccharides (Glycans) 3. Dextrin 4. Dextran  α -glucose units.  α -glucose units (glucosan).  Hydrolyzed to glucose Structure by α-dextrinase.  Storage polysaccharide in yeasts &  Used as mucilage. bacteria.  Produced by partial  Support medium for chromatography Functions hydrolysis of starch by of macromolecules. action of acids or  Replacement therapy in blood loss. enzymes.  Dental plaque as dextran synthesized from sucrose by oral bacteria. 5. Inulin 6. Cellulose  Fructose (fructosan). Structure  Hydrolyzed by inulinase  Formed of β-glucose units. in plants.  Most abundant natural polymer found in world (in cell walls of  No dietary importance in nearly all plants). human beings as inulinase  Extremely resistant to hydrolysis by is absent in human. acid & digestive tract amylase So, Functions  Diet for diabetic patient. it can stimulate peristaltic  Inulin clearance test to movement & prevent constipation. determine glomerular  Bacteria in gut of ruminant animals filtration rate. secrete cellulase (β- glucosidase) which can hydrolyze cellulose. DR. El-Sawy 3  Biochemistry Polysaccharides (Glycans) Starch Glycogen (animal starch) Dextrin  α-D glucose units (glucosan).  α-glucose units (glucosan).  α -glucose units.  2 Layers: Amylose & Amylopectin  It is highly branched.  Hydrolyzed to  Branches once every 10 glucose glucose by α- Structure  Branches once every 30 linkages. units (more branched than dextrinase.  Hydrolyzed by salivary & pancreatic amylopectin). amylase to maltose & dextrins  Give red violet color with iodine.  Most common storage poly in plants.  Most common storage poly in Functions animals & human body.  Mucilage.  Found in : liver mainly 10% Dextran Inulin Cellulose Structure  α -glucose units (glucosan).  Formed of fructose (fructosan)  β-glucose units.  Storage form in yeast & bacteria  No dietary importance.  Most abundant natural polymer  Support medium for  Diet for diabetic patient. found in world. Functions chromatography.  Inulin clearance test determine  Stimulate peristaltic movement  Replacement therapy. GFR. & prevent constipation.  Dental plaque. DR. El-Sawy 4  Biochemistry Polysaccharides (Glycans) Agar Def  A polysaccharide isolated from marine red algae. Structure  Composed of agarose & agaropectin.  Agarose gel  chromatography & electrophoresis. Functions  Nutrient agar  culture media used in microbiology. Proteoglycan  All of GAGs except Hyaluronic acid & Heparin are found Def covalently attached to protein to form proteoglycan.  Cartilage  consists of a core protein to which the linear Site carbohydrate chains are covalently attached. DR. El-Sawy 5  Biochemistry Polysaccharides (Glycans) GAGs (Muco-poly-saccharides)  Long linear (unbranched) heteropolysaccharide chains Def  Composed of a repeating disaccharide unit (acidic sugar - amino sugar) Amino sugar Acid sugar  D-glucosamine or D-galactosamic  D-glucuronic or L-iduronic.  Its amino group is usually acetylated, sometimes sulphated. DR. El-Sawy 6  Biochemistry Polysaccharides (Glycans) Chondotin Keratan Dermatan Heparin Heparan Hyaluronic acid Glucuronic acid or Glucuronic acid or Sugar Acid Glucuronic acid. No uronic acid. L-iduronic acid. Glucuronic acid. iduronic acid. Iduronic acid. Glucosamine & Amino sugar Galactosamine Galactosamine Glucosamine Glucosamine Glucosamine galactose -6- sulfate. Acetylated Acetylated Non acetylated Acetylated Sulfated Sulfated Sulfated Sulfated More Sulfated Sulfated Non sulfated Cartilage- tendons - ligaments  Synovial fluid of  Skin.  Intracellular joints.  Bone  Extracellular GAG. Site  Blood vessels. granules of mast  Vitreous humor of  Heart valves  Cornea  Basement memb.  Heart valves. cells. eye & skin.  Aorta.  Connective Tissue. Protective - supportive  Replaces  Component of cell  Shock absorbing. Main function  Most abundant hyaloronic acid in  Anticoagulant. surface  lubricant. GAG. aged skin & blood vessels. DR. El-Sawy 7  Biochemistry Polysaccharides (Glycans)  are proteins which contain oligosaccharide chains covalently Definition attached to amino acid side chains (serine threonine aspargine) residue of aminoacid.  The carbohydrate part consists of oligosaccharide chains.  These chains are attached to protein via OH of serine and Structure threonine residues (O – glycosidic bond) or the amide N of asparagine (N – glycosidic bond)  Glycoproteins could be found as: A. Extracellular glycoproteins secreted by the cell e.g. 1- Antibodies and some hormones. 2- Most proteins in the blood except albumin. Significance 3- Gastrointestinal tract mucus. B. Intracellular glycoproteins as lysosomal enzymes. C. Membrane - bound glycoproteins e.g. blood group antigens. DR. El-Sawy 8  Biochemistry Polysaccharides (Glycans)  Blood group in humans (ABO blood grouping) is based on : the antigenic differences determined by the type of glycoprotein present on the surface of red blood cells.  Two antigen glycoproteins, A and B are present. Type A  Have type A glycoproteins. Type B  Have type B glycoproteins. Type AB  Have both types. Type O  Both A and B antigens are absent DR. El-Sawy 9  Biochemistry Polysaccharides (Glycans)  Samia, a 46 years old female, went to a dermatologist asking for a medication for her dry wrinkled skin  The doctor prescribed a magical anti aging lotion to be used for 6 months. Q : Why doctor prescribes this lotion ?  In the connective tissues HA is associated with collagen.  HA content of skin and synovial fluid decreases as age advances hyaluronic acid is replaced by dermatan sulfate.  Dermatan sulfate is not a good lubricant, hence age related pains develop in old people. DR. El-Sawy 10