Carbohydrates

• carbohydrates are the most abundant class of organic compounds found in living things
• during photosynthesis in plants, carbon dioxide, and water combined to form the sugar glucose
• thousands of glucose molecules, combine to form the much larger cellulose molecule, which constitutes the structural framework of plants
• glucose molecules may also use to form molecules of starch which are stored in the seeds and serve as food for growing plant
• The most basic units of carbohydrates are simple sugars, or monosaccharides
• when two simple sugars combine, the resulting carbohydrate is a disaccharide
• Long chain of repeating units of repeating units of monosaccharides makes up a polysaccharide
• classification of monosaccharides, depending under content, and the number of carbon atoms they have

  • aldose
  • ketose
• The simplest monosaccharides

  • triose glyceraldehyde
  • dihydroxyacetone
• hexose such as glucose and fructose are utilized as energy sources for respiration and as building blocks of larger molecules
• pentoses such as ribose and ribulose are used in the synthesis of ribonucleic acid and the deoxyribonucleic acid, coenzymes, and adenosine triphosphate
• An aldopentose is an aldose with five carbon atoms
• ketohexose is a six carbon ketose
• glycosidic bond is a type of covalent bond that links a carbohydrate unit to another
• condensation reaction involves the elimination of water
• hydrolysis is the reverse of condensation reaction in which the glycosidic linkage in the disaccharide is broken
• sucrose, also known as stable sugar or cane sugar, is found in many plants
• lactose or milk sugar is composed of glucose and galactose
• Maltose, which is made up of two glucose units, is the initial product of the digestion of starch
• examples of disaccharide

  • sucrose (table sugar)= glucose + fructose
  • Lactose (milk sugar)= glucose + galactose
  • maltose (malt sugar)= glucose + glucose
• carbohydrates that contain an aldehyde group which can be oxidized to a carboxylic acid group, are known as reducing sugars
• The common reagent used to test for the presence of reducing sugar

  • Benedict’s solution
  • Fehling’s solution
  • Tollens’ reagent
• examples of polysaccharides

  • Starch
  • Glycogen
  • Cellulose
• polysaccharide are composed of long chain monosaccharide units
• Iodine-potassium iodide reagent is used to test for the presence of starch.
• primary function of carbohydrates and living organisms are as follows

  • Primary source of energy
  • Intermediate substances in respiration
  • Energy storage
  • Structure
  • Transport
  • Recognition of molecules that pass through the cell membrane
• examples of monosaccharides

  • Glucose (blood sugar)
  • Fructose (fruit sugar)
  • Galactose (found in milk with glucose)
• biomolecules - any molecules that are produced by a living organism, including large macromolecules, such as proteins, polysaccharides, lipids, and nucleic acid
• elements that contain in carbohydrates

  • Carbon
  • Hydrogen
  • Oxygen