Unit 1 - Key Questions

• Monomer

  Smaller units from which large molecules are made
• Polymer

  Molecules made from many monomers joined together
• 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
• Maltose

  A disaccharide formed from the condensation reaction between 2 glucose molecules
• Sucrose

  A disaccharide formed from the condensation reaction between a glucose and a fructose molecule
• Lactose

  A disaccharide formed from the condensation reaction between glucose and a galactose molecule
• Isomer

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

  • Alpha (a) glucose
  • Beta (B) glucose
• Difference between alpha and beta glucose


  The OH group on carbon 1 of a-glucose is below the ring, on ẞ-glucose it is above
• Monosaccharides have the general formula Cn(H2O)n
• Polysaccharide

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

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

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

  A complex carbohydrate, a polysaccharide made from multiple B-glucose molecules
• Molecules that make up starch

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

  Heavily branched polymer of a-glucose molecules, linked at 1-4 glycosidic bonds, branched with 1-6 glycosidic bonds
• Glycogen's structure and function

  Insoluble so does not affect water potential and osmosis, Insoluble so 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 a-glucose molecules, linked at 1-4 glycosidic bonds, branched with 1-6 glycosidic bonds
• Starch's structure

  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 a-glucose so easily transported and used for respiration, Branched so more enzymes can hydrolyse bonds simultaneously
• Basic structure of cellulose

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

  Alternative B-glucose molecules are turned upside down
• Cellulose's structure


  Made up of B-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
• Cellulose molecules form hydrogen bonds with each other to make microfibrils, microfibrils join to make macrofibrils, macrofibrils join to make fibres, fibres are insoluble and tough
• Purpose of glycogen

  It is an insoluble store of glucose in animals.
• What is the purpose of starch?

  It is an insoluble store of glucose in plants.
• What is the purpose of cellulose?

  it is an insoluble structural molecule for plants, found in plant cell walls
• Reducing sugars

  • Glucose
  • Galactose
  • Fructose
  • Lactose
  • Maltose
• Non-reducing sugars

  • Sucrose
• Benedict's test

  Tests for reducing sugars
• Benedict's test for reducing sugars


  1. Add equal volumes of sample and Benedict's reagent

  2. Gently heat for 5 minutes

  3. If reducing sugar present, colour changes from blue to red/green/orange
• Test for non-reducing sugars

  1. If no colour change in Benedict's test

  2. Add sample to equal volume of HCl

  3. Slowly add sodium hydrogen carbonate

  4. Re-test with Benedict's reagent while gently heating for 5 minutes

  5. If sugar is present, colour will turn from blue to yellow/green/orange/brick-red