Cacbohydrat

CACBOHYDRAT1CÁC ĐẠI PHÂN TỬ2CARBOHYDRATESSugars and their polymersGeneral formula ~ (CH2O)nC:H:O ratio 1:2:1Possess numerous polar covalent bondsForm H-bondsInteract favorably with waterHydrophilic3ROLES OF CARBOHYDRATESKey roles of carbohydratesShort-term energy storageLonger-term energy storageStructural rolesCell communication4ROLES OF CARBOHYDRATESShort-term energy storageMonosaccharides (“simple sugars”) are the simplest carbohydratese.g., Glucose, fructose, galactose, ribose, etc.Readily burned to release energy5ROLES OF CARBOHYDRATESShort-term energy storageDisaccharides consists of two covalently linked monosaccharidese.g., Sucrose, lactose, maltose, etc.Readily hydrolyzed to form monosaccharides6LACTOSE INTOLERANCEVirtually all humans can digest lactose during infancy and early childhoodMilk is an important food source early in lifeInfants produce the enzyme lactaseHydrolyzes lactose into the monosaccharides glucose and galactose7LACTOSE INTOLERANCEProduction of insufficient amounts of lactase results in lactose intoleranceLactose intolerance is due to lactase insufficiencyVarious symptomsNausea, cramps, bloating, gas, diarrhea, etc.X8LACTOSE INTOLERANCELactose intolerance is the normal situation for adult humansLactase production generally begins to decline at about age 2Lactase production generally halts by about age 4Similar declines seen in other mammalsSuch individuals become lactose intolerantX9LACTOSE INTOLERANCEThe frequency of lactose intolerance varies widely throughout the worldOver 90% of humans overall~4% of Swedes~100% of individuals from certain African and Asian populationsWhy do these rates differ so widely?10LACTOSE INTOLERANCEDomestication of plants and animals began rather recentlySheep, cattle, wheat, and barley were domesticated slightly over 10,000 years ago in the Near EastProfoundly altered the way people livedPopulations settled down and cultivated their own foodPopulations began to growCattle, sheep, grains, and lifestyle reached Western Europe a few millennia later11LACTOSE INTOLERANCEMutations causing lactase to be produced throughout adult life occurred in Western EuropeThis mutation was beneficial in populations involved in intensive dairy farmingNatural selection increased its frequency in such populationsLactose tolerance evolved in environments where milk is a major source of nutritionA similar mutation also occurred in the Fulani people of Western Africa a couple thousand years ago12LACTOSE INTOLERANCEDairy farming was the cultural practice that drove the evolution of lactose toleranceHighest levels of lactase deficiency in Asian populations not involved in dairy farmingLow levels of lactase deficiency in European populations with long histories of dairy farmingLow levels of lactase deficiency in West African populations relying extensively on milk in their diets13LACTOSE INTOLERANCEWestern Europeans colonized other areas of the world over the past five centuriesGene conferring lactase traveled with themFrequency of lactose tolerance increased in contacted populations14ROLES OF CARBOHYDRATESLonger-term energy storageStarch and glycogen are storage polysaccharidesPlants store excess sugars as starchAnimals store excess sugars as glycogenMonosaccharides can be released via hydrolysis15ROLES OF CARBOHYDRATESStructural rolesCellulose is a major component of plant cell wallsMost abundant organic compound on earthPolymer of glucose16ROLES OF CARBOHYDRATESStructural rolesThe covalent linkages between monomers differ between starch and celluloseDifferent three-dimensional shapesLinkages between starch monomers are easily hydrolyzedVery few organisms can hydrolyze linkages between cellulose monomersLack the required enzymes17ROLES OF CARBOHYDRATESStructural rolesSome microbes can digest cellulosee.g., Cellulose-digesting bacteria in a cow’s rumene.g., Cellulose-digesting microbes in a termite’s gutThese relationships are examples of mutualismBoth organisms benefit from the interactionHow?18ROLES OF CARBOHYDRATESStructural rolesChitin is a major component of fungal cell walls and arthropod exoskeletonsHardened with calcium carbonate in arthropodsStructure similar to cellulose19ROLES OF CARBOHYDRATES20ROLES OF CARBOHYDRATESCell communicationGlycoproteins and glycolipids on cell surface21TÀI LIỆU THAM KHẢOCampbell, Neil A. and Reese, Jane B. Biology, 7th edition. Pearson Education, Inc. 2005.Campbell, Neil A., Reese, Jane B., Taylor, Martha R., and Simon, Eric J. Biology, Concepts and Connections, 5th edition. Pearson Education, Inc. 2006.Nester, Eugene W., Anderson, Denise G., Roberts, C. Evans Jr., and Nester, Martha T. Microbiology, A Human Perspective, 5th edition. McGraw-Hill Companies, Inc. 2007.Limson, Janice. 2002.