CARBOHYDRATES Dr. Madushani Silva (MBBS)North Colombo Teaching Hospital – Ragama
Carbohydrates • Carbohydrates are called carbohydrates because they are essentially hydrates of carbon (i.e. they are composed of carbon and water and have a composition of (CH2O)n.
The major nutritional role of carbohydrates is to provide energy • digestible carbohydrates provide 4 kilocalories per gram. • No single carbohydrate is essential
Photosynthesis: Sun’s energy becomes part of glucose molecule energy Carbon dioxide Water Chlorophyll GLUCOSE 6 CO2 + 6 H20 + energy (sun) C6H12O6 + 6 O2
Types of Carbohydrates • Monosacchrides • Disaccharides Contain 2 monosacchride units • Polysacchrides Contain many monosacchride units
Monosacchrides • Three Carbons = Triose • Four Carbons = Tetrose • Five Carbons = Pentose • Six Carbons = Hexose
LACTOSE INTOLERANCE: Many healthy people, adults and children have the inability to digest lactose. It maybe inherited or acquired and results from a deficiency of the enzyme LACTASE. Lactase is necessary to breakdown lactose to galactose and glucose.
Lactulose • Heated milk (small amounts), mainly synthetic • Not hydrolyzed by intestinal enzymes, but fermented by intestinal bacteria; used as a mild osmotic laxative
Complex carbohydrates • Oligosaccharides • Polysaccharides
Polysaccharides • Homopolysaccrarides • Heteropolysaccarides Pure Congugated
Homopolysaccrarides • Starch • Glycogen • Dietary fiber
Heteropolysaccarides • Pure Pectin Gums Glycosaminoglycans
Conjugated Protein Proteoglycans (Carbo. constitute a major portion ) Glycoproteins (Proteins constitute a major portion) Lipids Glycolipids
Starch • Major storage carbohydrate in higher plants
Starch • Amylose – long straight glucose chains (a1-4) • Amylopectin – branched every 24-30 glc residues (a 1-6) • Provides 80% of dietary calories in humans worldwide
Glycogen G • Major storage carbohydrate in animals G G G G G G G G G G a 1-6 link G G G G a 1-4 link G G G G
also known as animal starch • stored in muscle and liver • complete hydrolysis yields glucose
Long straight glucose chains (a1-4) • Branched every 4-8 glc residues (a 1-6) • More branched than starch • Less osmotic pressure • Easily mobilized G G G G G G G G G G G a 1-6 link G G G G a 1-4 link G G G G
Glycosaminoglycans (mucopolysaccharides) • Linear polymers of repeating disaccharides • Complex carbohydrates containing amino sugars and uronic acids. • Glycosaminoglycans tend to be negatively charged, because of the prevalence of acidic groups.
Glycosaminoglycans • Hyaluronic acid (Glass): lubricants in synovial fluid , eye, cartilage and tendons; hyaluronidase secreted by bacteria — bacteria invasion. Similar enzyme for sperm to penetrate ovum. • Chondroitin sulfate (Cartilage): tensile strength pf cartilage, tendons and ligament, aorta. • Dermatan sulfate (Skin): skin, blood vessel and heart valves. Pliability of skin.
Glycosaminoglycans • Keratan sulfates (horn): cornea, horn, hair, hoof, nails, claws, no uronic acid. • Heparin (liver): made in mast cell- a anticoagulant with highest negative charge density, release to blood, inhibit blood clotting by binding to antithrombin III - bind to and inhibit thrombin, a protease essential to blood clotting.
Proteoglycan • They may be attached to a protein molecule to form a proteoglycan.
Proteoglycan glycosaminoglycansthat are covalently linked to serine residues of specific core proteins. The glycosaminoglycan chain is synthesized by sequential addition of sugar residues to the core protein.
Fibers • Found in food derived from plants • Includes polysaccharides such as cellulose, hemicellulose, pectins, gums and mucilages • Also includes non-polysaccharides such as lignin, cutins and tannins
Fibers • Fibers are not a source of energy because Human digestive enzymes cannot break down fibers • The bacteria in human GI tract can breakdown some fibers.
classification of fibers based on their solubilities in water • Soluble fibers • Insoluble fibers
classification of fibers based on their solubilities in water (1)Soluble fibers: includes gum,pectin, some hemicellulose and mucilages found in fruits, oats, barley and legumes .
Soluble fibers Actions on body: (i) Delay GI transit(benefits digestive disorders) (ii) Delay glucose absorption (benefits diabetes) (iii) Lowers blood cholesterol(benefits heart disease)
classification of fibers based on their solubilities in water (2) Insoluble fibers: includes cellulose, many hemicellulose, lignin found in wheat bran , corn bran, whole grain bread, cereals and vegetables (carrot, cabbage)
Insoluble fibers Actions in body: (i)Accelerates GI transit and increases fecal weight(promotes bowel movement) (ii) Slows starch hydrolysis and delays glucose absorption(Benefits diabetes)
2005 Dietary Guidelines for Americans Recommends… “ Consume 3 or more servings (or oz. equivalents) of whole-grain products per day, with the rest of the recommended grains coming from enriched or whole-grain products. In general, at least half the grains should come fromwhole grains.”
Exercise…… • Comment on the importance of dietary fibers in the example shown by the picture below
Dietary carbohydrates • Starch • Sucrose • Glucose and fructose • Lactose • Cellulose • Other plant polysaccharides Digestible Non-digestible by humans
Only monosaccharides are absorbed into the bloodstream from the gut. Digestion of carbohydrates involves their hydrolysis into monosaccharides