Carbohydrates

• Biological Molecules


  Key molecules required to build structures that enable organisms to function
• Key biological molecules


  • Carbohydrates
  • Proteins
  • Lipids
  • Nucleic Acids
  • Water

  
• Monomers


  Smaller units from which larger molecules are made
• Polymers


  Molecules made from a large number of monomers joined together in a chain
• Macromolecules


  Very large molecules containing 1000 or more atoms and having a high molecular mass
• Carbon atoms


  • Can form four covalent bonds, making compounds very stable
  • Can form covalent bonds with oxygen, nitrogen and sulfur
  • Can bond to form straight chains, branched chains or rings

  
• Polymerisation


  The process where small subunits (monomers) bond together to form large molecules (polymers)
• Types of carbohydrates

  • Monosaccharides
  • Disaccharides
  • Polysaccharides

  
• Covalent bond


  The sharing of two or more electrons between two atoms

  
• Nonpolar covalent bond


  Electrons are shared equally between atoms

  
• Polar covalent bond


  Electrons are shared unequally between atoms, with one atom being more electronegative

  
• Condensation


  Also known as dehydration synthesis, where monomers combine by covalent bonds to form polymers or macromolecules and water is removed
• Hydrolysis


  The breaking of covalent bonds in polymers when water is added
• Reducing sugars


  Can donate electrons, becoming the reducing agent, and can be detected using Benedict's test
• Non-reducing sugars


  Cannot donate electrons and must be hydrolysed before a Benedict's test can be carried out
• Glucose


  The most well-known carbohydrate monomer, existing in alpha and beta forms
• Glycosidic bond


  The covalent bond formed between two hydroxyl groups of monosaccharides to create disaccharides and polysaccharides
• Hydrolysis of glycosidic bonds


  The breaking of glycosidic bonds when water is added, catalysed by enzymes
• Sucrose is a non-reducing sugar that can be hydrolysed to glucose and fructose
• Hydrolytic reactions


  Catalysed by enzymes, different to those present in condensation reactions
• Hydrolytic reactions


  • Digestion of food in the alimentary tract
  • Breakdown of stored carbohydrates in muscle and liver cells for use in cellular respiration
• Hydrolysis Reaction


  Glycosidic bonds are broken by the addition of water
• Sucrose is a non-reducing sugar which gives a negative result in a Benedict's test
• Sucrose hydrolysis


  1. Heating with hydrochloric acid provides the water that hydrolyses the glycosidic bond

  2. Results in two monosaccharides that will produce a positive Benedict's test
• Breaking the Glycosidic Bond

  A molecule of glucose and a molecule of fructose are formed when one molecule of sucrose is hydrolysed
• Chromatography


  A technique that can be used to separate a mixture into its individual components
• Disaccharides


  • Monosaccharides can join together via condensation reactions to form disaccharides
  • The new chemical bond that forms between two monosaccharides is known as a glycosidic bond
• Common examples of disaccharides


  • Maltose
  • Sucrose
  • Lactose
• Maltose


  The sugar formed in the production and breakdown of starch
• Sucrose


  The main sugar produced in plants
• Lactose


  A sugar found only in milk
• All three common examples of disaccharides have the formula C12H22O11
• Maltose


  Formed from two α-glucose monomers
• Sucrose


  Formed from α-glucose and fructose monomers
• Starch and Glycogen


  Polysaccharides, macromolecules that are polymers formed by many monosaccharides joined by glycosidic bonds
• Starch and Glycogen


  • Compact (so large quantities can be stored)
  • Insoluble (so will have no osmotic effect)
• Starch


  The storage polysaccharide of plants, stored as granules in plastids
• Amylose


  One of the two polysaccharides that form starch, an unbranched helix-shaped chain with 1,4 glycosidic bonds between aplha-glucose molecules
• Amylopectin


  One of the two polysaccharides that form starch, has 1,4 glycosidic bonds between alpha-glucose molecules but also 1,6 glycosidic bonds forming branches
• Glycogen


  The storage polysaccharide of animals and fungi, highly branched and not coiled