Biologically Important Molecules - Carbohydrates

BIOLOGICALLY IMPORTANT MOLECULES CARBOHYDRATES • a group of organic compounds that contain C, H and O in the ratio 1:2:1 respectively • the general chemical formula is (CH2O)n, where n = # of carbon atoms • contain either an aldehyde or ketone group and hydroxyl groups • 3 main groups are monosaccharides, disaccharides and polysaccharides Monosaccharides • also called simple sugars • contain between 3-6 carbon atoms • readily soluble in water Examples: Glucose (C6H12O6) = blood sugar; primary source of energy for cells Fructose (C6H12O6) = fruit sugar Galactose (C6H12O6) = milk sugar *The above compounds all have the SAME molecular formula but different structural formulas; they are called STRUCTURAL ISOMERS Comparison of Linear Structural Formulas • Source of image: http://credit-help.biz/img/2551/monosaccharides1350254591202972.jpg *Hexose and pentose monosaccharides readily form ring structures when they are dissolved in water. Comparison of Ring Structures • Source of image: http://2012books.lardbucket.org/books/an-introduction-tonutrition/section_08/f9aa2d5666715b168c2b58737e8a31ba.jpg Alpha(α) and Beta(β) Configuration of Glucose (Memorize) • Source of image: https://wikispaces.psu.edu/download/attachments/40047583/image-3.jpg Disaccharides • formed by linking 2 monosaccharides via the removal of H2O; this is called a condensation reaction and the linkage is called a glycosidic linkage • Examples: glucose + fructose → sucrose + H2O glucose + galactose → lactose + H2O α-glucose + α-glucose → maltose + H2O β- glucose + β- glucose → cellobiose + H2O Digestion/Hydrolysis of Disaccharides • disaccharides are soluble in water, BUT are too large to enter cells • must be digested into monosaccharides in order to enter cells • requires the addition of H2O and specialized molecules called enzymes Examples: sucrose + H2O → glucose + fructose https://youtu.be/XAw6DH1SMAc lactose + H2O → glucose + galactose maltose + H2O → α-glucose + α-glucose cellobiose + H2O → β-glucose + β-glucose • a lack of or insufficient amount of lactase results in a condition known as lactose intolerance; symptoms usually occur within 2 hrs of ingesting lactose and include bloating, gas, flatulence, cramps and diarrhea • How can this be treated? Polysaccharides • polymers of hundreds/thousands of monosaccharide subunits • some are straight chains whereas others are branched molecules • main functions are energy storage and structural support Examples: Plant Starch = main energy storage molecule in plants; found in seeds, stems, leaves, fruits and roots 2 types: 1) Amylose = straight chain polymer of α-glucose molecules Source of Image: https://www.smartkitchen.com/resource/print/amylopectin 2) Amylopectin = branched polymer of α-glucose molecules Source of Image: https://www.smartkitchen.com/resource/print/amylopectin Glycogen = storage form of glucose in animals • similar in structure to amylopectin but more highly branched • stored in the liver and skeletal muscle • provides a source of glucose during periods of strenuous physical activity and between meals • can be depleted in a day if not replenished Cellulose • straight chain polymer of β-glucose molecules joined by β-1,4-glycosidic linkages Source of Image: http://www.easychem.com.au/production-of-materials/biomass-research/cellulose • most abundant organic compound in the world • hydrogen bonds can form between chains forming fibres • fibres can be used by humans to make paper, as well as cotton and linen clothing Importance of Cellulose to the Human Diet • humans, as well as many other animals, lack the enzymes necessary to digest cellulose • as a result, cellulose passes through our digestive system relatively unchanged; it is often referred to as dietary fibre, roughage or bulk • its presence serves to help move things along and thus promotes normal/regular bowel movements, as well as preventing constipation What are some other benefits of a high fibre diet? How do herbivores or even termites digest cellulose? • these organisms do not have the enzymes that are necessary to digest cellulose either but they have microbes in their digestive systems that assist them in cellulose digestion • https://www.youtube.com/watch?v=9-z0f5GnSs • chitin is cellulose like polymer that forms the external skeletons of insects and crustaceans and is also found in the cell walls of fungi Source of Image : https://courses.lumenlearning.com/ap1/chapter/organic-compounds-essential-to-human-functioning/