Key Questions 1

• What is a Monomer?


  Smaller units from which large molecules are made
• What is a Polymer?


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


  • Monosaccharide
  • Amino acids
  • Nucleotides
• Reaction that joins monomers together

  Condensation reaction
• Condensation reaction


  Two monomers are bonded together, water is formed as a by-product
• Hydrolysis reaction


  Two monomers are separated by breaking a bond, water is used up in this reaction
• Monomers that make up a polysaccharide

  • Monosaccharides
• Common monosaccharides


  • Glucose
  • Galactose
  • Fructose
• Reaction that forms the bond between two monosaccharides


  Condensation reaction
• Glycosidic bond


  Bond that forms when monosaccharides join
• Disaccharide


  A molecule made from 2 monosaccharides
• How a disaccharide is formed

  Condensation reaction between 2 monosaccharides
• Isomer


  Molecules where the molecular formula stays the same, but the structural formula is different
• Isomers of glucose


  • Alpha glucose
  • Beta glucose
• Difference between alpha and beta glucose

  The OH group on carbon 1 of a glucose is below the ring in alpha, above the ring in beta
• Polysaccharide


  A complex carbohydrate formed from the condensation reactions of many monosaccharides
• Polysaccharides


  • Glycogen
  • Starch
  • Cellulose
• Glycogen


  A complex carbohydrate, a polysaccharide made from multiple alpha-glucose molecules
• Starch


  A complex carbohydrate, a polysaccharide made from multiple alpha-glucose molecules
• Cellulose


  A complex carbohydrate, a polysaccharide made from multiple beta-glucose molecules
• Purpose of glycogen


  Insoluble store of glucose in animals
• Purpose of starch


  Insoluble store of glucose in plants
• Purpose of cellulose


  Insoluble structural molecule for plants, found in plant cell walls
• Components of starch


  • Amylose (helical molecule)
  • Amylopectin (branched molecule)
• Structure of glycogen


  Linked at 1-4 glycosidic bonds, branched with 1-6 glycosidic bonds
• Relationship between glycogen structure and function


  Insoluble so does not affect water potential and osmosis

  Insoluble so it does not diffuse out of cells

  Compact due to helical structure so lots of glucose can be stored in small spaces

  Highly branched so many ends can be simultaneously hydrolysed by enzymes
• Structure of starch


  Lightly branched polymer of alpha-glucose molecules, linked at 1-4 glycosidic bonds, branched with 1-6 glycosidic bonds
• Relationship between starch structure and function


  Insoluble so doesn't affect water potential and osmosis

  Large and insoluble so doesn't diffuse out of cells

  Compact due to helical structure so lots of glucose stored in small space

  Hydrolysed to form alpha-glucose so easily transported and used for respiration

  Branched so more enzymes can hydrolyse bonds simultaneously
• Basic structure of cellulose

  Straight chains of beta-glucose molecules, bonded with 1,4 glycosidic bonds
• Arrangement of monosaccharides in cellulose

  Alternative beta-glucose molecules are turned upside down
• Relationship between cellulose structure and function


  Made up of beta-glucose so form long, straight unbranched chains/chains run parallel to each other and are crossed, linked by hydrogen bonds which add collective strength/molecules are grouped to form microfibrils which are also grouped to form fibres which provides more strength
• Examples of reducing sugars

  • All monosaccharides (glucose, galactose, fructose), some disaccharides (lactose, maltose)
• What the Benedict's test tests for

  Reducing sugar
• Benedict's test for reducing sugars


  Add equal volumes of sample and Benedict's reagent, gently heat for 5 minutes, colour change from blue to red/green/orange indicates reducing sugar present
• Test for non-reducing sugars

  Add sample to HCl, then slowly add sodium hydrogen carbonate, re-test with Benedict's reagent, colour change indicates non-reducing sugar present
• Positive result in Benedict's test


  Reducing sugar reacts with blue Cu2+ to make brick-red Cu
• Test for starch


  Iodine solution turns from yellow/orange to blue/black if starch is present
• Role of lipids


  Source of energy, also for waterproofing/insulation/protection
• Main groups of lipids

  • Triglycerides
  • Phospholipids
• Components of a triglyceride

  1 glycerol molecule and 3 fatty acids bonded with a condensation reaction